1.
Weight
–
In science and engineering, the weight of an object is usually taken to be the force on the object due to gravity. Weight is a vector whose magnitude, often denoted by an italic letter W, is the product of the m of the object. The unit of measurement for weight is that of force, which in the International System of Units is the newton. For example, an object with a mass of one kilogram has a weight of about 9.8 newtons on the surface of the Earth, in this sense of weight, a body can be weightless only if it is far away from any other mass. Although weight and mass are scientifically distinct quantities, the terms are often confused with other in everyday use. There is also a tradition within Newtonian physics and engineering which sees weight as that which is measured when one uses scales. There the weight is a measure of the magnitude of the force exerted on a body. Typically, in measuring an objects weight, the object is placed on scales at rest with respect to the earth, thus, in a state of free fall, the weight would be zero. In this second sense of weight, terrestrial objects can be weightless, ignoring air resistance, the famous apple falling from the tree, on its way to meet the ground near Isaac Newton, is weightless. Further complications in elucidating the various concepts of weight have to do with the theory of relativity according to gravity is modelled as a consequence of the curvature of spacetime. In the teaching community, a debate has existed for over half a century on how to define weight for their students. The current situation is that a set of concepts co-exist. Discussion of the concepts of heaviness and lightness date back to the ancient Greek philosophers and these were typically viewed as inherent properties of objects. Plato described weight as the tendency of objects to seek their kin. To Aristotle weight and levity represented the tendency to restore the order of the basic elements, air, earth, fire. He ascribed absolute weight to earth and absolute levity to fire, archimedes saw weight as a quality opposed to buoyancy, with the conflict between the two determining if an object sinks or floats. The first operational definition of weight was given by Euclid, who defined weight as, weight is the heaviness or lightness of one thing, compared to another, operational balances had, however, been around much longer. According to Aristotle, weight was the cause of the falling motion of an object
Weight
–
Ancient Greek official bronze weights dating from around the 6th century BC, exhibited in the
Ancient Agora Museum in Athens, housed in the
Stoa of Attalus.
Weight
–
Weighing grain, from the Babur-namah
Weight
–
This
top-fuel dragster can accelerate from zero to 160 kilometres per hour (99 mph) in 0.86 seconds. This is a horizontal acceleration of 5.3 g. Combined with the vertical g-force in the stationary case the
Pythagorean theorem yields a g-force of 5.4 g. It is this g-force that causes the driver's weight if one uses the operational definition. If one uses the gravitational definition, the driver's weight is unchanged by the motion of the car.
Weight
–
Measuring weight versus mass
2.
Mass
–
In physics, mass is a property of a physical body. It is the measure of a resistance to acceleration when a net force is applied. It also determines the strength of its gravitational attraction to other bodies. The basic SI unit of mass is the kilogram, Mass is not the same as weight, even though mass is often determined by measuring the objects weight using a spring scale, rather than comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity and this is because weight is a force, while mass is the property that determines the strength of this force. In Newtonian physics, mass can be generalized as the amount of matter in an object, however, at very high speeds, special relativity postulates that energy is an additional source of mass. Thus, any body having mass has an equivalent amount of energy. In addition, matter is a defined term in science. There are several distinct phenomena which can be used to measure mass, active gravitational mass measures the gravitational force exerted by an object. Passive gravitational mass measures the force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force, according to Newtons second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A bodys mass also determines the degree to which it generates or is affected by a gravitational field and this is sometimes referred to as gravitational mass. The standard International System of Units unit of mass is the kilogram, the kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. Then in 1889, the kilogram was redefined as the mass of the prototype kilogram. As of January 2013, there are proposals for redefining the kilogram yet again. In this context, the mass has units of eV/c2, the electronvolt and its multiples, such as the MeV, are commonly used in particle physics. The atomic mass unit is 1/12 of the mass of a carbon-12 atom, the atomic mass unit is convenient for expressing the masses of atoms and molecules. Outside the SI system, other units of mass include, the slug is an Imperial unit of mass, the pound is a unit of both mass and force, used mainly in the United States
Mass
–
Depiction of early
balance scales in the
Papyrus of Hunefer (dated to the
19th dynasty, ca. 1285 BC). The scene shows
Anubis weighing the heart of Hunefer.
Mass
–
The kilogram is one of the seven
SI base units and one of three which is defined ad hoc (i.e. without reference to another base unit).
Mass
–
Galileo Galilei (1636)
Mass
–
Distance traveled by a freely falling ball is proportional to the square of the elapsed time
3.
Newton (unit)
–
The newton is the International System of Units derived unit of force. It is named after Isaac Newton in recognition of his work on classical mechanics, see below for the conversion factors. One newton is the force needed to one kilogram of mass at the rate of one metre per second squared in direction of the applied force. In 1948, the 9th CGPM resolution 7 adopted the name newton for this force, the MKS system then became the blueprint for todays SI system of units. The newton thus became the unit of force in le Système International dUnités. This SI unit is named after Isaac Newton, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, section 5.2. Newtons second law of motion states that F = ma, where F is the applied, m is the mass of the object receiving the force. The newton is therefore, where the symbols are used for the units, N for newton, kg for kilogram, m for metre. In dimensional analysis, F = M L T2 where F is force, M is mass, L is length, at average gravity on earth, a kilogram mass exerts a force of about 9.8 newtons. An average-sized apple exerts about one newton of force, which we measure as the apples weight, for example, the tractive effort of a Class Y steam train and the thrust of an F100 fighter jet engine are both around 130 kN. One kilonewton,1 kN, is 102.0 kgf,1 kN =102 kg ×9.81 m/s2 So for example, a platform rated at 321 kilonewtons will safely support a 32,100 kilograms load. Specifications in kilonewtons are common in safety specifications for, the values of fasteners, Earth anchors. Working loads in tension and in shear, thrust of rocket engines and launch vehicles clamping forces of the various moulds in injection moulding machines used to manufacture plastic parts
Newton (unit)
–
Base units
4.
Kilogram
–
The kilogram or kilogramme is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype of the Kilogram. The avoirdupois pound, used in both the imperial and US customary systems, is defined as exactly 0.45359237 kg, making one kilogram approximately equal to 2.2046 avoirdupois pounds. Other traditional units of weight and mass around the world are also defined in terms of the kilogram, the gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimeter of water at the melting point of ice. The final kilogram, manufactured as a prototype in 1799 and from which the IPK was derived in 1875, had an equal to the mass of 1 dm3 of water at its maximum density. The kilogram is the only SI base unit with an SI prefix as part of its name and it is also the only SI unit that is still directly defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories. Three other base units and 17 derived units in the SI system are defined relative to the kilogram, only 8 other units do not require the kilogram in their definition, temperature, time and frequency, length, and angle. At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, the decision was originally deferred until 2014, in 2014 it was deferred again until the next meeting. There are currently several different proposals for the redefinition, these are described in the Proposed Future Definitions section below, the International Prototype Kilogram is rarely used or handled. In the decree of 1795, the term gramme thus replaced gravet, the French spelling was adopted in the United Kingdom when the word was used for the first time in English in 1797, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with kilogram having become by far the more common, UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling. In the 19th century the French word kilo, a shortening of kilogramme, was imported into the English language where it has used to mean both kilogram and kilometer. In 1935 this was adopted by the IEC as the Giorgi system, now known as MKS system. In 1948 the CGPM commissioned the CIPM to make recommendations for a practical system of units of measurement. This led to the launch of SI in 1960 and the subsequent publication of the SI Brochure, the kilogram is a unit of mass, a property which corresponds to the common perception of how heavy an object is. Mass is a property, that is, it is related to the tendency of an object at rest to remain at rest, or if in motion to remain in motion at a constant velocity. Accordingly, for astronauts in microgravity, no effort is required to hold objects off the cabin floor, they are weightless. However, since objects in microgravity still retain their mass and inertia, the ratio of the force of gravity on the two objects, measured by the scale, is equal to the ratio of their masses. On April 7,1795, the gram was decreed in France to be the weight of a volume of pure water equal to the cube of the hundredth part of the metre
Kilogram
–
A domestic-quality one-kilogram weight made of
cast iron (the
credit card is for scale). The shape follows
OIML recommendation R52 for cast-iron hexagonal weights
Kilogram
–
Measurement of weight – gravitational attraction of the measurand causes a distortion of the spring
Kilogram
–
Measurement of mass – the gravitational force on the measurand is balanced against the gravitational force on the weights.
Kilogram
–
The Arago kilogram, an exact copy of the "Kilogramme des Archives" commissioned in 1821 by the US under supervision of French physicist
François Arago that served as the US's first kilogram standard of mass until 1889, when the US converted to primary metric standards and received its current kilogram prototypes, K4 and K20.
5.
Analytical balance
–
An analytical balance is a class of balance designed to measure small mass in the sub-milligram range. The measuring pan of a balance is inside a transparent enclosure with doors so that dust does not collect. This enclosure is called a draft shield. Also, the sample must be at room temperature to prevent natural convection from forming air currents inside the enclosure from causing an error in reading, electronic analytical scales measure the force needed to counter the mass being measured rather than using actual masses. As such they must have calibration adjustments made to compensate for gravitational differences and they use an electromagnet to generate a force to counter the sample being measured and outputs the result by measuring the force needed to achieve balance. Such measurement device is called electromagnetic force restoration sensor, triple beam balance is an instrument used to measure mass very precisely. The device has reading error of +/-0.05 gram, the name refers to the three beams including the middle beam which is the largest size, the front beam which is the medium size, and the far beam which is the smallest size. The difference in size of the beams indicate the difference in weights, the reading scale can be enumerated that the middle beam reads in 100 gram increments, the front beam can read from 0 to 10 grams, and the far beam can read in 10 gram increments. The triple beam balance can be used to measure mass directly from the objects, find mass by difference for liquid, the parts of triple beam balance are identified as the following. Base is the part of triple beam balance. The use of base is to use both hands for carrying Pan is where specimen that is measuring is placed, scale pointer is the pointer that indicate the equality in mass of the object on the pan and the mass on the beam. Zero adjustment knob is used only when the triple beam balance is not zero at the beginning of the lab to adjust the scale pointer to align with zero, beams are three bars which indicate 0 to 10 grams,10 grams, and 100 gram increments. Riders are the sliding pointers used to mass in grams of the mass on the pan. Before using triple beam balance, the pointer should be at zero. The zero adjustment knob can be used to adjust the scale pointer, place the objects on the pan and adjust the riders. The hundred rider should be adjusted and follow by the tens rider. Adjust the ones rider until the pointer is at zero again
Analytical balance
–
Mettler digital analytical balance with 0.1 mg readability.
Analytical balance
–
Mechanical analytical balance
Analytical balance
–
Automated analytical balance, 1950s
6.
Uniform Penny Post
–
The Uniform Penny Post was a component of the comprehensive reform of the Royal Mail, the UKs official postal service, that took place in the 19th century. The reforms were a government initiative to eradicate the abuse and corruption of the existing service, richard Cobden and John Ramsey McCulloch, both advocates of free trade, attacked the Conservative governments policies of privilege and protection, including their archaic postal system. McCulloch, in 1833, advanced the view that nothing more to facilitate commerce than the safe, speedy. However, Hill did not include a timetable for the introduction of a penny post in his proposal. Nonetheless, Hills 1838 proposal paved the way for the 1840 Act which introduced the Uniform Penny Post. In his proposal, Hill also called for official pre-printed envelopes and adhesive postage stamps as alternative ways of getting the sender to pay for postage and this was a lower rate than before, when the cost of postage was usually more than 4d. The reform did not settle the issue of who paid for the postage, as of 2013 the value of one penny in 1840 ranges from 32p to 4.89, the latter based on mean income. It would appear that the cost to an established semi-skilled man of sending a letter in 1840 can be represented by approximately 1, financially, the penny post scheme was a disaster. More than thirty years elapsed before revenues were back to the pre-1840 level, the real benefits were the encouragement and support that the availability of cheap letterpost communication gave to the development of transport links, education, commerce and social cohesion. Uniform Fourpenny Post Penny Black Postage stamps and postal history of Great Britain Ashurst, facts and reasons in support of Mr. Rowland Hills plan for a universal penny postage. Penny Postage Centenary, An account of Rowland Hills great reform of 1840, london, The Postal History Society,1940 144p. Grimwood-Taylor, James L. Derby, Published for the author by Cavendish Philatelic Auctions Ltd.1990 ISBN 0-9515626-0-6, london, Charles Knight and Company,1844 84p. Great Britain, The Development and Introduction of Uniform Penny Postage, gerrards Cross, the author,2006 15p. Uniform Penny Post, Handstruck Paid Postage Stamps of England and Wales 1840-1853, sutton Coldfield, GBPS,2013 ISBN 978-0-907630-24-1, 32p
Uniform Penny Post
–
Royal Mail Post Office Regulations
handbill giving details of the Uniform Penny Post, dated January 7, 1840
7.
Spring scale
–
A spring scale or spring balance or newton meter is a type of weighing scale. It consists of spring fixed at one end with a hook to attach an object at the other and it works by Hookes Law, which states that the force needed to extend a spring is proportional to the distance that spring is extended from its rest position. Therefore, the markings on the spring balance are equally spaced. A spring scale can not measure mass, only weight, also, the spring in the scale can permanently stretch with repeated use. A spring scale will only read correctly in a frame of reference where the acceleration in the axis is constant. This can be shown by taking a spring scale into an elevator, if two or more spring balances are hung one below the other in series, each of the scales will read approximately the same, the full weight of the body hung on the lower scale. The scale on top would read slightly heavier due to supporting the weight of the lower scale itself. Spring balances come in different sizes, generally, small scales that measure newtons will have a less firm spring than larger ones that measure tens, hundreds or thousands of newtons or even more depending on the scale of newtons used. The largest spring scale ranged in measurement from 5000-8000 newtons, a spring balance may be labeled in both units of force and mass. Strictly speaking, only the values are correctly labeled. Main uses of spring balances are industrial, especially related to weighing heavy loads such as trucks, storage silos and they are also common in science education as basic accelerators. They are used when the accuracy afforded by other types of scales can be sacrificed for simplicity, cheapness, a spring balance measures the weight of an object by opposing the force of gravity acting with the force of an extended spring. The first spring balance in Britain was made around 1770 by Richard Salter of Bilston and he and his nephews John & George founded the firm of George Salter & Co. still notable makers of scales and balances, who in 1838 patented the spring balance. They also applied the same spring balance principle to steam locomotive safety valves, weighing scale Media related to spring balance at Wikimedia Commons Media related to spring scales at Wikimedia Commons
Spring scale
–
Spring balance, measuring in
gram.
Spring scale
–
Example of spiral balancer for sash windows
8.
Spring (device)
–
A spring is an elastic object used to store mechanical energy. Springs are usually out of spring steel. There are a number of spring designs, in everyday usage the term often refers to coil springs. When a spring is compressed or stretched from its resting position, the rate or spring constant of a spring is the change in the force it exerts, divided by the change in deflection of the spring. That is, it is the gradient of the force versus deflection curve, an extension or compression springs rate is expressed in units of force divided by distance, for example lbf/in or N/m. A torsion spring is a spring that works by twisting, when it is twisted about its axis by an angle, a torsion springs rate is in units of torque divided by angle, such as N·m/rad or ft·lbf/degree. The inverse of spring rate is compliance, that is, if a spring has a rate of 10 N/mm, the stiffness of springs in parallel is additive, as is the compliance of springs in series. Springs are made from a variety of materials, the most common being spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel, some non-ferrous metals are also used including phosphor bronze and titanium for parts requiring corrosion resistance and beryllium copper for springs carrying electrical current. Simple non-coiled springs were used throughout history, e. g. the bow. In the Bronze Age more sophisticated spring devices were used, as shown by the spread of tweezers in many cultures, coiled springs appeared early in the 15th century, in door locks. The first spring powered-clocks appeared in that century and evolved into the first large watches by the 16th century, in 1676 British physicist Robert Hooke discovered Hookes law which states that the force a spring exerts is proportional to its extension. Compression spring – is designed to operate with a compression load, flat spring – this type is made of a flat spring steel. Machined spring – this type of spring is manufactured by machining bar stock with a lathe and/or milling operation rather than a coiling operation, since it is machined, the spring may incorporate features in addition to the elastic element. Machined springs can be made in the load cases of compression/extension, torsion. Serpentine spring - a zig-zag of thick wire - often used in modern upholstery/furniture, the most common types of spring are, Cantilever spring – a spring which is fixed only at one end. Coil spring or helical spring – a spring is of two types, Tension or extension springs are designed to become longer under load and their turns are normally touching in the unloaded position, and they have a hook, eye or some other means of attachment at each end. Compression springs are designed to become shorter when loaded and their turns are not touching in the unloaded position, and they need no attachment points
Spring (device)
–
Helical or coil springs designed for tension.
Spring (device)
–
A heavy-duty helical spring designed for compression and tension.
Spring (device)
–
The
English longbow – a simple but very powerful spring made of
yew, measuring 2 m (6 ft 6 in) long, with a 470 N (105
lbf) draw force
Spring (device)
–
A machined spring incorporates several features into one piece of bar stock
9.
Torque
–
Torque, moment, or moment of force is rotational force. Just as a force is a push or a pull. Loosely speaking, torque is a measure of the force on an object such as a bolt or a flywheel. For example, pushing or pulling the handle of a wrench connected to a nut or bolt produces a torque that loosens or tightens the nut or bolt, the symbol for torque is typically τ, the lowercase Greek letter tau. When it is called moment of force, it is denoted by M. The SI unit for torque is the newton metre, for more on the units of torque, see Units. This article follows US physics terminology in its use of the word torque, in the UK and in US mechanical engineering, this is called moment of force, usually shortened to moment. In US physics and UK physics terminology these terms are interchangeable, unlike in US mechanical engineering, Torque is defined mathematically as the rate of change of angular momentum of an object. The definition of states that one or both of the angular velocity or the moment of inertia of an object are changing. Moment is the term used for the tendency of one or more applied forces to rotate an object about an axis. For example, a force applied to a shaft causing acceleration, such as a drill bit accelerating from rest. By contrast, a force on a beam produces a moment, but since the angular momentum of the beam is not changing. Similarly with any force couple on an object that has no change to its angular momentum and this article follows the US physics terminology by calling all moments by the term torque, whether or not they cause the angular momentum of an object to change. The concept of torque, also called moment or couple, originated with the studies of Archimedes on levers, the term torque was apparently introduced into English scientific literature by James Thomson, the brother of Lord Kelvin, in 1884. A force applied at an angle to a lever multiplied by its distance from the levers fulcrum is its torque. A force of three newtons applied two metres from the fulcrum, for example, exerts the same torque as a force of one newton applied six metres from the fulcrum. More generally, the torque on a particle can be defined as the product, τ = r × F, where r is the particles position vector relative to the fulcrum. Alternatively, τ = r F ⊥, where F⊥ is the amount of force directed perpendicularly to the position of the particle, any force directed parallel to the particles position vector does not produce a torque
Torque
10.
Lever
–
A lever is a machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. A lever is a body capable of rotating on a point on itself. On the basis of the location of fulcrum, load and effort and it is one of the six simple machines identified by Renaissance scientists. A lever amplifies an input force to provide an output force. The ratio of the force to the input force is the mechanical advantage of the lever. The word lever entered English about 1300 from Old French, in which the word was levier and this sprang from the stem of the verb lever, meaning to raise. The verb, in turn, goes back to the Latin levare, itself from the adjective levis, the words primary origin is the Proto-Indo-European stem legwh-, meaning light, easy or nimble, among other things. The PIE stem also gave rise to the English word light, the earliest remaining writings regarding levers date from the 3rd century BC and were provided by Archimedes. Give me a place to stand, and I shall move the Earth with it is a remark of Archimedes who formally stated the correct mathematical principle of levers. The distance required to do this might be exemplified in astronomical terms as the distance to the Circinus galaxy - about 9 million light years. It is assumed that in ancient Egypt, constructors used the lever to move, a lever is a beam connected to ground by a hinge, or pivot, called a fulcrum. The ideal lever does not dissipate or store energy, which there is no friction in the hinge or bending in the beam. This is known as the law of the lever, the mechanical advantage of a lever can be determined by considering the balance of moments or torque, T, about the fulcrum. T1 = F1 a, T2 = F2 b where F1 is the force to the lever. The distances a and b are the distances between the forces and the fulcrum. Since the moments of torque must be balanced, T1 = T2, the mechanical advantage of the lever is the ratio of output force to input force, M A = F2 F1 = a b. Levers are classified by the positions of the fulcrum, effort. It is common to call the force the effort and the output force the load or the resistance
Lever
–
Levers can be used to exert a large force over a small distance at one end by exerting only a small force over a greater distance at the other.
Lever
–
A lever in balance
Lever
–
This is an engraving from Mechanics Magazine published in London in 1824.
11.
Force
–
In physics, a force is any interaction that, when unopposed, will change the motion of an object. In other words, a force can cause an object with mass to change its velocity, force can also be described intuitively as a push or a pull. A force has both magnitude and direction, making it a vector quantity and it is measured in the SI unit of newtons and represented by the symbol F. The original form of Newtons second law states that the net force acting upon an object is equal to the rate at which its momentum changes with time. In an extended body, each part usually applies forces on the adjacent parts, such internal mechanical stresses cause no accelation of that body as the forces balance one another. Pressure, the distribution of small forces applied over an area of a body, is a simple type of stress that if unbalanced can cause the body to accelerate. Stress usually causes deformation of materials, or flow in fluids. In part this was due to an understanding of the sometimes non-obvious force of friction. A fundamental error was the belief that a force is required to maintain motion, most of the previous misunderstandings about motion and force were eventually corrected by Galileo Galilei and Sir Isaac Newton. With his mathematical insight, Sir Isaac Newton formulated laws of motion that were not improved-on for nearly three hundred years, the Standard Model predicts that exchanged particles called gauge bosons are the fundamental means by which forces are emitted and absorbed. Only four main interactions are known, in order of decreasing strength, they are, strong, electromagnetic, weak, high-energy particle physics observations made during the 1970s and 1980s confirmed that the weak and electromagnetic forces are expressions of a more fundamental electroweak interaction. Since antiquity the concept of force has been recognized as integral to the functioning of each of the simple machines. The mechanical advantage given by a machine allowed for less force to be used in exchange for that force acting over a greater distance for the same amount of work. Analysis of the characteristics of forces ultimately culminated in the work of Archimedes who was famous for formulating a treatment of buoyant forces inherent in fluids. Aristotle provided a discussion of the concept of a force as an integral part of Aristotelian cosmology. In Aristotles view, the sphere contained four elements that come to rest at different natural places therein. Aristotle believed that objects on Earth, those composed mostly of the elements earth and water, to be in their natural place on the ground. He distinguished between the tendency of objects to find their natural place, which led to natural motion, and unnatural or forced motion
Force
–
Aristotle famously described a force as anything that causes an object to undergo "unnatural motion"
Force
–
Forces are also described as a push or pull on an object. They can be due to phenomena such as
gravity,
magnetism, or anything that might cause a mass to accelerate.
Force
–
Though
Sir Isaac Newton 's most famous equation is, he actually wrote down a different form for his second law of motion that did not use
differential calculus.
Force
–
Galileo Galilei was the first to point out the inherent contradictions contained in Aristotle's description of forces.
12.
Tension (physics)
–
Tension is the opposite of compression. At the atomic level, when atoms or molecules are pulled apart each other and gain potential energy with a restoring force still existing. Each end of a string or rod under such tension will pull on the object it is attached to, to restore the string/rod to its relaxed length. In physics, tension, as a force, as an action-reaction pair of forces. The ends of a string or other object transmitting tension will exert forces on the objects to which the string or rod is connected and these forces due to tension are also called passive forces. Tension in a string is a scalar quantity. A string or rope is often idealized as one dimension, having length but being massless with zero cross section. If there are no bends in the string, as occur with vibrations or pulleys, then tension is a constant along the string, by Newtons Third Law, these are the same forces exerted on the ends of the string by the objects to which the ends are attached. If the string curves around one or more pulleys, it still have constant tension along its length in the idealized situation that the pulleys are massless and frictionless. A vibrating string vibrates with a set of frequencies that depend on the strings tension and these frequencies can be derived from Newtons laws of motion. Each microscopic segment of the string pulls on and is pulled upon by its neighboring segments, tension = τ where x is the position along the string. If the string has curvature, then the two pulls on a segment by its two neighbors will not add to zero, and there will be a net force on that segment of the string, causing an acceleration. With solutions that include the various harmonics on a stringed instrument, tension is also used to describe the force exerted by the ends of a three-dimensional, continuous material such as a rod or truss member. Such a rod elongates under tension, a system is in equilibrium when the sum of all forces is zero. ∑ F → =0 For example, consider a system consisting of an object that is being lowered vertically by a string with tension, T, at a constant velocity. ∑ F → = T → + m g → =0 A system has a net force when a force is exerted on it. Acceleration and net force always exist together, ∑ F → ≠0 For example, consider the same system as above but suppose the object is now being lowered with an increasing velocity downwards therefore there exists a net force somewhere in the system. In this case, negative acceleration would indicate that | m g | > | T |
Tension (physics)
13.
Gravity
–
Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies. Since energy and mass are equivalent, all forms of energy, including light, on Earth, gravity gives weight to physical objects and causes the ocean tides. Gravity has a range, although its effects become increasingly weaker on farther objects. The most extreme example of this curvature of spacetime is a hole, from which nothing can escape once past its event horizon. More gravity results in time dilation, where time lapses more slowly at a lower gravitational potential. Gravity is the weakest of the four fundamental interactions of nature, the gravitational attraction is approximately 1038 times weaker than the strong force,1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, gravity has an influence on the behavior of subatomic particles. On the other hand, gravity is the dominant interaction at the macroscopic scale, for this reason, in part, pursuit of a theory of everything, the merging of the general theory of relativity and quantum mechanics into quantum gravity, has become an area of research. While the modern European thinkers are credited with development of gravitational theory, some of the earliest descriptions came from early mathematician-astronomers, such as Aryabhata, who had identified the force of gravity to explain why objects do not fall out when the Earth rotates. Later, the works of Brahmagupta referred to the presence of force, described it as an attractive force. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and this was a major departure from Aristotles belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass may fall slower in an atmosphere, galileos work set the stage for the formulation of Newtons theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newtons theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the position of the planet. A discrepancy in Mercurys orbit pointed out flaws in Newtons theory, the issue was resolved in 1915 by Albert Einsteins new theory of general relativity, which accounted for the small discrepancy in Mercurys orbit. The simplest way to test the equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the rate when other forces are negligible
Gravity
–
Sir Isaac Newton, an English physicist who lived from 1642 to 1727
Gravity
Gravity
–
Two-dimensional analogy of spacetime distortion generated by the mass of an object. Matter changes the geometry of spacetime, this (curved) geometry being interpreted as gravity. White lines do not represent the curvature of space but instead represent the
coordinate system imposed on the curved spacetime, which would be
rectilinear in a flat spacetime.
Gravity
–
Ball falling freely under gravity. See text for description.
14.
Calibration
–
Calibration in measurement technology and metrology is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known accuracy, strictly, the term calibration means just the act of comparison, and does not include any subsequent adjustment. The calibration standard is normally traceable to a national standard held by a National Metrological Institute and this definition states that the calibration process is purely a comparison, but introduces the concept of Measurement uncertainty in relating the accuracies of the device under test and the standard. The increasing need for accuracy and uncertainty and the need to have consistent. In many countries a National Metrology Institute will exist which will maintain primary standards of measurement which will be used to provide traceability to customers instruments by calibration. The NMI supports the metrological infrastructure in that country by establishing an unbroken chain, examples of National Metrology Institutes are NPL in the UK, NIST in the United States, PTB in Germany and many others. This may be done by national standards laboratories operated by the government or by private firms offering metrology services, quality management systems call for an effective metrology system which includes formal, periodic, and documented calibration of all measuring instruments. ISO9000 and ISO17025 standards require that these actions are to a high level. To communicate the quality of a calibration the calibration value is often accompanied by a traceable uncertainty statement to a confidence level. This is evaluated through careful uncertainty analysis, some times a DFS is required to operate machinery in a degraded state. Whenever this does happen, it must be in writing and authorized by a manager with the assistance of a calibration technician. Measuring devices and instruments are categorized according to the quantities they are designed to measure. These vary internationally, e. g. NIST 150-2G in the U. S. the standard instrument for each test device varies accordingly, e. g. a dead weight tester for pressure gauge calibration and a dry block temperature tester for temperature gauge calibration. g. This is the perception of the instruments end-user, however, very few instruments can be adjusted to exactly match the standards they are compared to. For the vast majority of calibrations, the process is actually the comparison of an unknown to a known. The calibration process begins with the design of the instrument that needs to be calibrated. The design has to be able to hold a calibration through its calibration interval, in other words, the design has to be capable of measurements that are within engineering tolerance when used within the stated environmental conditions over some reasonable period of time. Having a design with these characteristics increases the likelihood of the measuring instruments performing as expected
Calibration
–
An example of a device whose calibration is off: a
weighing scale that reads ½ ounce without any load.
Calibration
–
Indirect reading design showing a Bourdon tube from the front (left) and the rear (right).
Calibration
Calibration
–
Gas pump with rotary flow indicator (yellow) and nozzle (red)
15.
Grocery store
–
A grocery store is a retail store that primarily sells food. A grocer is a seller of food. Grocery stores often offer non-perishable food that is packaged in cans, bottles and boxes, with also having fresh produce, butchers, delis. Large grocery stores that stock significant amounts of products, such as clothing. Some large supermarkets also include a pharmacy, and customer service, redemption, in the United States, Canada, and United Kingdom, supermarkets and convenience stores are sometimes described as grocery businesses, or simply grocers. Some grocery stores form the centerpiece of a complex that includes other facilities, such as gas stations. This setup is especially common in the United Kingdom, with chains such as Tesco. Some groceries specialize in the foods of a nationality or culture, such as Italian, Polish. These stores are known as ethnic markets and may serve as gathering places for immigrants. In many cases, the range of products carried by larger supermarkets has reduced the need for such speciality stores. The variety and availability of food is no longer restricted by the diversity of locally grown food or the limitations of the growing season. Beginning as early as the 14th century, a grocer was a dealer in dry goods such as spices, peppers, sugar. These items were bought in bulk, hence the term grocer from the French grossier meaning wholesaler, as increasing numbers of staple foodstuffs became available in cans and other less-perishable packaging, the trade expanded its province. Today, grocers deal in a range of staple food-stuffs including such perishables as meats, produce. These trading posts evolved into larger retail businesses known as general stores and these facilities generally dealt only in dry goods such as flour, dry beans, baking soda, and canned foods. Many rural areas still contain general stores that sell goods ranging from cigars to imported napkins, traditionally, general stores have offered credit to their customers, a system of payment that works on trust rather than modern credit cards. This allowed farm families to buy staples until their harvest could be sold, the first self-service grocery store, Piggly Wiggly, was opened in 1916 in Memphis, Tennessee by Clarence Saunders, an inventor and entrepreneur. The early supermarkets began as chains of grocers shops, a small grocery store may also compete by locating in a mixed commercial-residential area close to, and convenient for, its customers
Grocery store
–
The
produce section in a supermarket
Grocery store
–
Packaged food aisles in a
hypermarket.
Grocery store
–
A grocery store in Nizwa, Oman
Grocery store
16.
Pressure gauge
–
Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure in a unit are called pressure gauges or vacuum gauges. A manometer is an example as it uses a column of liquid to both measure and indicate pressure. Likewise the widely used Bourdon gauge is a device which both measures and indicates, and is probably the best known type of gauge. A vacuum gauge is a pressure gauge used to measure the pressures lower than the ambient atmospheric pressure. Other methods of pressure measurement involve sensors which can transmit the pressure reading to an indicator or control system. Everyday pressure measurements, such as for vehicle tire pressure, are made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to other specific reference. Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure, to distinguish a negative pressure, the value may be appended with the word vacuum or the gauge may be labeled a vacuum gauge. These are further divided into two subcategories, high and low vacuum, the applicable pressure ranges of many of the techniques used to measure vacuums have an overlap. Hence, by combining different types of gauge, it is possible to measure system pressure continuously from 10 mbar down to 10−11 mbar. Differential pressure is the difference in pressure between two points, the zero reference in use is usually implied by context, and these words are added only when clarification is needed. Tire pressure and blood pressure are gauge pressures by convention, while atmospheric pressures, deep vacuum pressures, for most working fluids where a fluid exists in a closed system, gauge pressure measurement prevails. Pressure instruments connected to the system will indicate pressures relative to the current atmospheric pressure, the situation changes when extreme vacuum pressures are measured, absolute pressures are typically used instead. Differential pressures are used in industrial process systems. Differential pressure gauges have two ports, each connected to one of the volumes whose pressure is to be monitored. Moderate vacuum pressure readings can be ambiguous without the proper context, thus a vacuum of 26 inHg gauge is equivalent to an absolute pressure of 30 inHg −26 inHg =4 inHg. Atmospheric pressure is typically about 100 kPa at sea level, but is variable with altitude, if the absolute pressure of a fluid stays constant, the gauge pressure of the same fluid will vary as atmospheric pressure changes
Pressure gauge
–
The construction of a bourdon tube gauge. Construction elements are made of
brass.
Pressure gauge
–
A McLeod gauge, drained of mercury
Pressure gauge
–
Membrane-type manometer
Pressure gauge
–
Indicator side with card and dial
17.
Strain gauge
–
A strain gauge is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C, ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, as the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor, a strain gauge takes advantage of the physical property of electrical conductance and its dependence on the conductors geometry. Conversely, when a conductor is compressed such that it does not buckle, it will broaden and shorten, from the measured electrical resistance of the strain gauge, the amount of induced stress may be inferred. The gauge factor G F is defined as, G F = Δ R / R G ϵ where Δ R is the change in resistance caused by strain, R G is the resistance of the undeformed gauge, and ϵ is strain. For common metallic foil gauges, the factor is usually a little over 2. Foil gauges typically have active areas of about 2–10 mm² in size, with careful installation, the correct gauge, and the correct adhesive, strains up to at least 10% can be measured. An excitation voltage is applied to input leads of the network. Typical input voltages are 5 V or 12 V and typical output readings are in millivolts, foil strain gauges are used in many situations. Different applications place different requirements on the gauge, in most cases the orientation of the strain gauge is significant. Strain gauges are attached to the substrate with a special glue, the type of glue depends on the required lifetime of the measurement system. For short term measurements cyanoacrylate glue is appropriate, for long lasting installation epoxy glue is required, usually epoxy glue requires high temperature curing. The preparation of the surface where the gauge is to be glued is of the utmost importance. If these steps are not followed the strain gauge binding to the surface may be unreliable and unpredictable measurement errors may be generated, strain gauge based technology is utilized commonly in the manufacture of pressure sensors. The gauges used in pressure sensors themselves are made from silicon, polysilicon, metal film, thick film. Variations in temperature will cause a multitude of effects, the object will change in size by thermal expansion, which will be detected as a strain by the gauge. Resistance of the gauge will change, and resistance of the wires will change
Strain gauge
–
Mechanical strain gauge used to measure the growth of a crack in a masonry foundation. This one is installed on the
Hudson–Athens lighthouse
Strain gauge
–
Typical foil strain gauge. The gauge is far more sensitive to strain in the vertical direction than in the horizontal direction. The markings outside the active area help to align the gauge during installation.
18.
Electrical resistance
–
The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The inverse quantity is electrical conductance, and is the ease with which a current passes. Electrical resistance shares some parallels with the notion of mechanical friction. The SI unit of resistance is the ohm, while electrical conductance is measured in siemens. An object of uniform cross section has a proportional to its resistivity and length. All materials show some resistance, except for superconductors, which have a resistance of zero and this proportionality is called Ohms law, and materials that satisfy it are called ohmic materials. In other cases, such as a diode or battery, V and I are not directly proportional. The ratio V/I is sometimes useful, and is referred to as a chordal resistance or static resistance, since it corresponds to the inverse slope of a chord between the origin and an I–V curve. In other situations, the derivative d V d I may be most useful, in the hydraulic analogy, current flowing through a wire is like water flowing through a pipe, and the voltage drop across the wire is like the pressure drop that pushes water through the pipe. Conductance is proportional to how much flow occurs for a given pressure, the voltage drop, not the voltage itself, provides the driving force pushing current through a resistor. In hydraulics, it is similar, The pressure difference between two sides of a pipe, not the pressure itself, determines the flow through it, for example, there may be a large water pressure above the pipe, which tries to push water down through the pipe. But there may be a large water pressure below the pipe. If these pressures are equal, no water flows, in the same way, a long, thin copper wire has higher resistance than a short, thick copper wire. A pipe filled with hair restricts the flow of more than a clean pipe of the same shape. The difference between copper, steel, and rubber is related to their structure and electron configuration. In addition to geometry and material, there are other factors that influence resistance and conductance, such as temperature. Substances in which electricity can flow are called conductors, a piece of conducting material of a particular resistance meant for use in a circuit is called a resistor. Conductors are made of high-conductivity materials such as metals, in particular copper, Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs
Electrical resistance
–
A 6.5 MΩ
resistor, as identified by its
electronic color code (blue–green–black-yellow). An
ohmmeter could be used to verify this value.
Electrical resistance
–
Electromagnetism
Electrical resistance
–
Running current through a material with high resistance creates heat, in a phenomenon called
Joule heating. In this picture, a
cartridge heater, warmed by Joule heating, is
glowing red hot.
19.
Weighbridge
–
A Truck scale, weighbridge or railroad scale is a large set of scales, usually mounted permanently on a concrete foundation, that is used to weigh entire rail or road vehicles and their contents. By weighing the vehicle both empty and when loaded, the load carried by the vehicle can be calculated, the key component that uses a weighbridge in order to make the weigh measurement is load cells. Commercial scales have to be National Type Evaluation Program approved or certified.1, NTEP approved scales are generally considered those scales which are intended by the manufacturer for use in commercial applications where products are sold by weight. NTEP Approved is also known as Legal for Trade or complies with Handbook 44 and they are typically built from steel or concrete and by nature are extremely robust. In earlier versions the bridge is installed over a pit that contains levers that ultimately connect to a balance mechanism. The most complex portion of this type is the arrangement of levers underneath the weighbridge since the response of the scale must be independent of the distribution of the load, modern devices use multiple load cells that connect to an electronic equipment to totalize the sensor inputs. In either type of semi-permanent scale the weight readings are typically recorded in a hut or office. Many weighbridges are now linked to a PC which runs truck scale software capable of printing tickets, Truck scales can be used for two main purposes, Selling or charging by weight over the bridge Check weighing both axle weights and gross vehicle weights. This helps to stop axle overloading and possible heavy fines, since the weight of the vehicle carrying the goods is known they are a quick and easy way to measure the flow of bulk goods in and out of different locations. Similar to the full size truck scale these systems can be pit mounted with the weighing surface flush to the level of the roadway or surface mounted, for many uses weighbridges have been largely supplanted by simple and thin electronic weigh cells, over which a vehicle is slowly driven. A computer records the output of the cell and accumulates the total vehicle weight, the former two limits ensure the safety of bridges while the latter protects the road surface. Portable truck scales can also be found in use around the world, a portable truck scale will have lower frame work that can be placed on non-typical surfaces such as dirt. These scales retain the level of accuracy as a pit-type scale. The first portable truck scale record in the US was units operated by the Weight Patrol of the Los Angeles Motor Patrol in 1929, four such weighing units were used with one under each of the trucks wheels. Each unit could record up to 15,000 pounds, on-board scale Scale test car Weighing scale Weigh lock compression Load Cell
Weighbridge
–
A weighbridge at a gravel pit. The weighbridge is the two part platform over which trucks are driven. The upper works is auxiliary equipment for leveling the load in the truck and is not part of the scale. This scale uses electronic measuring equipment
Weighbridge
–
Electronic indicator for the bridge shown above. This allows input of the vehicle empty weight and can compute and display the amount of material
Weighbridge
–
A Griffith Elder full size weighbridge
20.
Bakery
–
A bakery is an establishment that produces and sells flour-based food baked in an oven such as bread, cookies, cakes, pastries, and pies. Some retail bakeries are also cafés, serving coffee and tea to customers who wish to consume the baked goods on the premises, baked goods have been around for thousands of years. The art of baking was developed early during the Roman Empire and it was a highly famous art as Roman citizens loved baked goods and demanded for them frequently for important occasions such as feasts and weddings etc. Due to the fame and desire that the art of baking received, around 300 BC, baking was introduced as an occupation, the bakers began to prepare bread at home in an oven, using mills to grind grain into the flour for their breads. The oncoming demand for baked goods vigorously continued and the first bakers guild was established in 168 BC in Rome and this drastic appeal for baked goods promoted baking all throughout Europe and expanded into the eastern parts of Asia. Bakers started baking breads and goods at home and selling out on the streets. This trend became common and soon, baked products were getting sold in streets of Rome, Germany, London and this resulted in a system of delivering the goods to households, as the demand for baked breads and goods significantly increased. This provoked the bakers to establish a place people could purchase baked goods for themselves. Therefore, in Paris, the first open-air bakery of baked goods was developed and since then, bakeries became a place to purchase delicious goods. By the colonial era, bakeries were commonly viewed as places to gather, world War II directly affected bread industries in the UK. Baking schools closed during this time so when the war did eventually end there was an absence of skilled bakers and this resulted in new methods being developed to satisfy the world’s desire for bread. Methods like, adding chemicals to dough, premixes and specialised machinery, unfortunately these old methods of baking were almost completely eradicated when these new methods were introduced and became industrialised. The old methods were seen as unnecessary and financially unsound, during this period there were not many traditional bakeries left, some bakeries provide services for special occasions or for people who have allergies or sensitivities to certain foods. Bakeries can provide a range of cakes designs such as sheet cakes, layer cakes, tiered cakes. Grocery stores and supermarkets, in countries, sell prepackaged or pre-sliced bread, cakes. They can also offer in-store baking and basic cake decoration
Bakery
–
Bakery in
Mahane Yehuda Market
Bakery
–
A woman working with a commercial oven at a bakery
Bakery
–
Bakery window with breads and cakes on display, 1936
Bakery
–
Types
21.
Grocery
–
A grocery store is a retail store that primarily sells food. A grocer is a seller of food. Grocery stores often offer non-perishable food that is packaged in cans, bottles and boxes, with also having fresh produce, butchers, delis. Large grocery stores that stock significant amounts of products, such as clothing. Some large supermarkets also include a pharmacy, and customer service, redemption, in the United States, Canada, and United Kingdom, supermarkets and convenience stores are sometimes described as grocery businesses, or simply grocers. Some grocery stores form the centerpiece of a complex that includes other facilities, such as gas stations. This setup is especially common in the United Kingdom, with chains such as Tesco. Some groceries specialize in the foods of a nationality or culture, such as Italian, Polish. These stores are known as ethnic markets and may serve as gathering places for immigrants. In many cases, the range of products carried by larger supermarkets has reduced the need for such speciality stores. The variety and availability of food is no longer restricted by the diversity of locally grown food or the limitations of the growing season. Beginning as early as the 14th century, a grocer was a dealer in dry goods such as spices, peppers, sugar. These items were bought in bulk, hence the term grocer from the French grossier meaning wholesaler, as increasing numbers of staple foodstuffs became available in cans and other less-perishable packaging, the trade expanded its province. Today, grocers deal in a range of staple food-stuffs including such perishables as meats, produce. These trading posts evolved into larger retail businesses known as general stores and these facilities generally dealt only in dry goods such as flour, dry beans, baking soda, and canned foods. Many rural areas still contain general stores that sell goods ranging from cigars to imported napkins, traditionally, general stores have offered credit to their customers, a system of payment that works on trust rather than modern credit cards. This allowed farm families to buy staples until their harvest could be sold, the first self-service grocery store, Piggly Wiggly, was opened in 1916 in Memphis, Tennessee by Clarence Saunders, an inventor and entrepreneur. The early supermarkets began as chains of grocers shops, a small grocery store may also compete by locating in a mixed commercial-residential area close to, and convenient for, its customers
Grocery
–
The
produce section in a supermarket
Grocery
–
Packaged food aisles in a
hypermarket.
Grocery
–
A grocery store in Nizwa, Oman
Grocery
22.
Delicatessen
–
A delicatessen or deli is a retail establishment that sells a selection of unusual or foreign prepared foods. Delicatessens originated in Germany during the 1700s and spread to the United States in the mid-1800s, European immigrants to the United States, especially Ashkenazi Jews, popularized the delicatessen in American culture beginning in the late 1800s. Delicatessen is a German loanword which first appeared in English in 1889 and is the plural of Delikatesse, in German it was originally a French loanword, délicatesse, meaning delicious things. Its root word is the Latin adjective delicatus, meaning giving pleasure, delightful, the first Americanized short version of this word, deli, came into existence c. 1954. The German food company Dallmayr is credited with being the first delicatessen created, in 1700, it became the first store to import bananas, mangoes, and plums to the German population from faraway places such as the Canary Islands and China. Over 300 years later, it remains the largest business of its kind in Europe, the first delicatessens to appear in the United States were in New York City in the mid-1800s, with the first known use of this word occurring in 1885. These catered to the German immigrant population living there, as the German-Jewish population increased in New York City during the mid- to late 1800s, kosher delicatessens began to open, the first was founded in 1889. In the United States, by the late 20th to early 21st centuries, supermarkets, local economy stores, and fast food outlets began using the word to describe sections of their stores. The decline of the deli as an independent retail establishment was most noted in New York City, from a high in the 1930s of about 1,500 Jewish delicatessens, in most of Australia, the term delicatessen retains its European meaning. Large supermarket chains often have a department, and independent delicatessens exist throughout the country. Both types of deli offer a variety of cured meats, sausages, pickled vegetables, dips, breads, Deli also denotes a small convenience store or milk bar in Western and South Australia, and some businesses use deli as part of their business name. Traditional delicatessens also exist in these states, with continental delicatessen sometimes used to indicate the European version, in Canada, both meanings of delicatessen are used. In Europe delicatessen means high-quality, expensive foods and stores, in German-speaking countries a common synonym is Feinkost, and shops which sell it are called Feinkostläden. Department stores often have a Delikatessenabteilung, European delicatessens include Fauchon in Paris, Dallmayr in Munich, Harrods and Fortnum & Mason in London, and Peck in Milan. Although U. S. -style delicatessens are also found in Europe, in Russia, shops and supermarket sections approximating US-style delis are called kulinariya and offer salads and main courses. Delicate meats and cheeses, cold-cut and sliced hot, are sold in a separate section, the Eliseevsky food store in central Moscow, with its fin de siècle decor, is similar to a European delicatessen. From the Tsarist era, it was preserved by the Soviets as an outlet for difficult-to-obtain Russian delicacies, delicatessens may also provide foods from other countries and cultures which is not readily available in local food stores. In Italy, the deli can be called gastronomia, negozio di specialità gastronomiche, in France it is nowadays known as a traiteur or épicerie fine
Delicatessen
–
An Italian delicatessen in Rome
Delicatessen
–
French delicacies, sold in delicatessens: foie gras with Sauternes wine
Delicatessen
–
A fish counter at
Harrods in London
Delicatessen
–
An Italian style delicatessen in
Five Dock, Sydney
23.
Seafood
–
Seafood is any form of sea life regarded as food by humans. Seafood prominently includes fish and shellfish, shellfish include various species of molluscs, crustaceans, and echinoderms. Historically, sea mammals such as whales and dolphins have been consumed as food, edible sea plants, such as some seaweeds and microalgae, are widely eaten as seafood around the world, especially in Asia. In North America, although not generally in the United Kingdom, for the sake of completeness, this article includes all edible aquatic life. The harvesting of seafood is usually known as fishing or hunting. Seafood is often distinguished from meat, although it is still animal and is excluded in a vegetarian diet. Seafood is an important source of protein in many diets around the world, most of the seafood harvest is consumed by humans, but a significant proportion is used as fish food to farm other fish or rear farm animals. Some seafoods are used as food for other plants, in these ways, seafoods are indirectly used to produce further food for human consumption. Products, such as oil and spirulina tablets are also extracted from seafoods. Some seafood is feed to fish, or used to feed domestic pets, such as cats. The harvesting, processing, and consuming of seafoods are ancient practices with archaeological evidence dating back well into the Paleolithic, isotopic analysis of the skeletal remains of Tianyuan man, a 40, 000-year-old modern human from eastern Asia, has shown that he regularly consumed freshwater fish. Archaeology features such as middens, discarded fish bones and cave paintings show that sea foods were important for survival. During this period, most people lived a lifestyle and were, of necessity. However, where there are examples of permanent settlements such as those at Lepenski Vir. The ancient river Nile was full of fish, fresh and dried fish were a food for much of the population. The Egyptians had implements and methods for fishing and these are illustrated in scenes, drawings. Some representations hint at fishing being pursued as a pastime, fishing scenes are rarely represented in ancient Greek culture, a reflection of the low social status of fishing. However, Oppian of Corycus, a Greek author wrote a treatise on sea fishing
Seafood
–
Seafood includes any form of food taken from the sea
Seafood
–
Various foods depicted in an Egyptian burial chamber, including fish, c. 1400 BC
Seafood
–
marine
pelagic
Seafood
–
marine
demersal
24.
Meat
–
Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat since prehistoric times, the advent of civilization allowed the domestication of animals such as chickens, sheep, pigs and cattle. This eventually led to their use in production on an industrial scale with the aid of slaughterhouses. Meat is mainly composed of water, protein, and fat and it is edible raw, but is normally eaten after it has been cooked and seasoned or processed in a variety of ways. Unprocessed meat will spoil or rot within hours or days as a result of infection with and decomposition by bacteria, most often, meat refers to skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as offal. The word meat comes from the Old English word mete, which referred to food in general, the term is related to mad in Danish, mat in Swedish and Norwegian, and matur in Icelandic and Faroese, which also mean food. The word mete also exists in Old Frisian to denote important food, differentiating it from swiets, paleontological evidence suggests that meat constituted a substantial proportion of the diet of even the earliest humans. Early hunter-gatherers depended on the hunting of large animals such as bison. Several breeds of sheep were established in ancient Mesopotamia and Egypt by 3500–3000 BC, today, more than 200 sheep-breeds exist. Cattle were domesticated in Mesopotamia after settled agriculture was established about 5000 BC, modern domesticated cattle fall into the groups Bos taurus and Bos indicus, both descended from the now-extinct aurochs. The breeding of cattle, cattle optimized for meat production as opposed to animals best suited for draught or dairy purposes. Domestic pigs, which are descended from boars, are known to have existed about 2500 BC in modern-day Hungary and in Troy, earlier pottery from Jericho. Pork sausages and hams were of commercial importance in Greco-Roman times. Pigs continue to be bred intensively as they are being optimized to produce meat best suited for meat products. Other animals are or have raised or hunted for their flesh. The type of meat consumed varies much between different cultures, changes over time, depending on such as tradition and the availability of the animals. The amount and kind of meat consumed also varies by income, horses are commonly eaten in France, Italy, Germany and Japan, among other countries. Horses and other mammals such as reindeer were hunted during the late Paleolithic in western Europe
Meat
–
Varieties of meat
Meat
–
A typical shoulder cut of
lamb
Meat
–
A
Hereford bull, a breed of cattle frequently used in beef production.
Meat
–
Blade steaks are an example of "red" meat
25.
Produce
–
Produce is a generalized term for a group of farm-produced crops and goods, including fruits and vegetables – meats, grains, oats, etc. are also sometimes considered produce. More specifically, the term often implies that the products are fresh. In supermarkets the term is used to refer to the section where fruit. Produce is the product sold by greengrocers, farmers markets. The term produce is used in the U. S. but is not typically used outside the agricultural sector in other English-speaking countries. In parts of the world including the U. S. produce is marked with small stickers bearing price look-up codes and these four- or five-digit codes are a standardized system intended to aid checkout and inventory control in produce markets. Although in most parts of the world forms of produce are available year-round. The seasonality of produce depends on variables such as climate and weather. Below is a general list of produce seasonality for north of and south of the tropics, including Canada, spring fruits are apricots, strawberries, cherries. Spring vegetables are peas and more delicate cabbages including mustard greens, baby lettuce, baby spinach, also in season are artichoke, asparagus, avocado, new potatoes, rhubarb. Summer fruits include some berries and stone fruit as well as melons, summer vegetables include beets, corn, cucumber, eggplant, green beans, tomatoes and zucchini. Autumn fruits includes apples, cranberries, grapes, figs, pears, autumn vegetables include many cultivars of wild cabbage. Root vegetables and winter squash are also in season, corn is in season and peas, seasonal in spring, are also seasonal in late autumn. Winter fruits include citrus and pomegranates, also seasonal in winter are some root vegetables as well as winter squash. Some produce, such as onions, lettuce, spinach and strawberries are seasonal year-round in subtropical climates, vegetables are optimally stored between 0° and 4. 4° Celsius to reduce respiration. Generally, vegetables should be stored at a high humidity, but cucubits and onions prefer dry, raw sprouts are among the most risky produce. Rinsing is a way to reduce the bacteria count on produce. Wastewater can be a source of contamination, due to contamination of water with fecal matter with salmonella or other bacteria, after Denmark eliminated salmonella in its chickens, attention has turned to vegetables as a source of illness
Produce
–
Produce on display at
La Boqueria market in
Barcelona, Spain.
Produce
–
A produce market in Germany
26.
RFID
–
Radio-frequency identification uses electromagnetic fields to automatically identify and track tags attached to objects. The tags contain electronically stored information, Passive tags collect energy from a nearby RFID readers interrogating radio waves. Active tags have a power source such as a battery. Unlike a barcode, the tag need not be within the line of sight of the reader, RFID is one method for Automatic Identification and Data Capture. These concerns resulted in standard specifications development addressing privacy and security issues, ISO/IEC18000 and ISO/IEC29167 use on-chip cryptography methods for untraceability, tag and reader authentication, and over-the-air privacy. ISO/IEC20248 specifies a digital data structure for RFID and barcodes providing data, source. This work is done within ISO/IEC JTC 1/SC31 Automatic identification, in 2014, the world RFID market is worth US$8.89 billion, up from US$7.77 billion in 2013 and US$6.96 billion in 2012. This includes tags, readers, and software/services for RFID cards, labels, fobs, the market value is expected to rise to US$18.68 billion by 2026. In 1945, Léon Theremin invented a tool for the Soviet Union which retransmitted incident radio waves with the audio information. Sound waves vibrated a diaphragm which slightly altered the shape of the resonator, similar technology, such as the IFF transponder, was routinely used by the allies and Germany in World War II to identify aircraft as friend or foe. Transponders are still used by most powered aircraft to this day, another early work exploring RFID is the landmark 1948 paper by Harry Stockman. Considerable research and development work has to be done before the basic problems in reflected-power communication are solved. Mario Cardullos device, patented on January 23,1973, was the first true ancestor of modern RFID, the basic Cardullo patent covers the use of RF, sound and light as transmission media. The original business plan presented to investors in 1969 showed uses in transportation, banking, security and medical. An early demonstration of reflected power RFID tags, both passive and semi-passive, was performed by Steven Depp, Alfred Koelle, and Robert Frayman at the Los Alamos National Laboratory in 1973, the portable system operated at 915 MHz and used 12-bit tags. This technique is used by the majority of todays UHFID and microwave RFID tags, the first patent to be associated with the abbreviation RFID was granted to Charles Walton in 1983. A radio-frequency identification system uses tags, or labels attached to the objects to be identified, two-way radio transmitter-receivers called interrogators or readers send a signal to the tag and read its response. RFID tags can be passive, active or battery-assisted passive
RFID
–
Small RFID chips, here compared to a grain of rice, are incorporated in consumer products, and
implanted in pets, for identification purposes
RFID
–
FasTrak, an RFID tag used for
electronic toll collection in California
RFID
–
Electronic Lock with RFID Card System, ANSI
RFID
–
Electronic key for RFID based lock system
27.
State of Florida
–
Florida /ˈflɒrᵻdə/ is a state located in the southeastern region of the United States. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia, to the east by the Atlantic Ocean, Florida is the 22nd-most extensive, the 3rd-most populous, and the 8th-most densely populated of the U. S. states. Jacksonville is the most populous municipality in the state and is the largest city by area in the contiguous United States, the Miami metropolitan area is Floridas most populous urban area. The city of Tallahassee is the state capital, much of the state is at or near sea level and is characterized by sedimentary soil. The climate varies from subtropical in the north to tropical in the south, the American alligator, American crocodile, Florida panther, and manatee can be found in the Everglades National Park. It was a location of the Seminole Wars against the Native Americans. Today, Florida is distinctive for its large Cuban expatriate community and high population growth, the states economy relies mainly on tourism, agriculture, and transportation, which developed in the late 19th century. Florida is also renowned for amusement parks, orange crops, the Kennedy Space Center, Florida has attracted many writers such as Marjorie Kinnan Rawlings, Ernest Hemingway and Tennessee Williams, and continues to attract celebrities and athletes. It is internationally known for golf, tennis, auto racing, by the 16th century, the earliest time for which there is a historical record, major Native American groups included the Apalachee, the Timucua, the Ais, the Tocobaga, the Calusa and the Tequesta. Florida was the first part of the continental United States to be visited and settled by Europeans, the earliest known European explorers came with the Spanish conquistador Juan Ponce de León. Ponce de León spotted and landed on the peninsula on April 2,1513 and he named the region La Florida. The story that he was searching for the Fountain of Youth is a myth, in May 1539, Conquistador Hernando de Soto skirted the coast of Florida, searching for a deep harbor to land. He described seeing a wall of red mangroves spread mile after mile, some reaching as high as 70 feet. Very soon, many smokes appeared along the whole coast, billowing against the sky, the Spanish introduced Christianity, cattle, horses, sheep, the Spanish language, and more to Florida. Both the Spanish and French established settlements in Florida, with varying degrees of success, in 1559, Don Tristán de Luna y Arellano established a settlement at present-day Pensacola, making it the first attempted settlement in Florida, but it was abandoned by 1561. Spain maintained tenuous control over the region by converting the tribes to Christianity. The area of Spanish Florida diminished with the establishment of English settlements to the north, the English attacked St. Augustine, burning the city and its cathedral to the ground several times. Florida attracted numerous Africans and African-Americans from adjacent British colonies who sought freedom from slavery, in 1738, Governor Manuel de Montiano established Fort Gracia Real de Santa Teresa de Mose near St
State of Florida
–
St. Augustine is the oldest city in the U.S., established in 1565 by Spain.
State of Florida
–
Flag
State of Florida
–
Aerial view of
Castillo De San Marcos (Florida).
State of Florida
–
The five flags of Florida from the right,
Spain (1565–1763), the
Kingdom of Great Britain, Spain (1784–1821), the
Confederacy, and the United States. France (flag not shown) also controlled part of Florida.
28.
Cafeteria
–
Cafeterias are different from coffeehouses, despite being the Spanish translation of the English term. Instead of table service, there are food-serving counters/stalls, either in a line or allowing arbitrary walking paths, customers take the food that they desire as they walk along, placing it on a tray. Alternatively, the patron is given a number and the item is brought to his table. For some food items and drinks, such as sodas, water, or the like, customers collect an empty container, pay at the check-out, free unlimited second servings are often allowed under this system. For legal purposes, this system is rarely, if at all, customers are either charged a flat rate for admission or pay at the check-out for each item. Some self-service cafeterias charge by the weight of items on a patrons plate, in universities and colleges, some students pay for three meals a day by making a single large payment for the entire semester. As cafeterias require few employees, they are found within a larger institution. For example, schools, colleges and their halls, department stores, hospitals, museums, military bases, prisons. At one time, upscale cafeteria-style restaurants dominated the culture of the Southern United States, and to a lesser extent the Midwest. There were numerous prominent chains of them, Bickfords, Morrisons Cafeteria, Piccadilly Cafeteria, S&W Cafeteria, Apple House, Lubys, K&W, Britling, Wyatts Cafeteria, currently two Midwestern chains still exist, Sloppy Jos Lunchroom and Mannys, which are both located in Illinois. There were also a number of chains, usually located in. These institutions, with the exception of K&W, went into a decline in the 1960s with the rise of fast food and were finished off in the 1980s by the rise of casual dining. A few chains — particularly Lubys and Piccadilly Cafeterias — continue to some of the gap left by the decline of the older chains. Some of the smaller Midwestern chains, such as MCL Cafeterias centered on Indianapolis, are very much in business. Perhaps the first self-service restaurant in the US was the Exchange Buffet in New York City, opened September 4,1885, Food was purchased at a counter, and patrons ate standing up. This represents the predecessor of two formats, the cafeteria, described below, and the automat, during the 1893 Worlds Columbian Exposition in Chicago, entrepreneur John Kruger built an American version of the smörgåsbords he had seen while traveling in Sweden. Emphasizing the simplicity and light fare, he called it the Cafeteria - Spanish for coffee shop, the exposition attracted over 27 million visitors in six months, and because of Krugers operation that America first heard the term and experienced the self-service dining format. Meanwhile, in mid-scale America, the chain of Childs Restaurants quickly grew from about 10 locations in New York City in 1890 to hundreds across the US and Canada by 1920
Cafeteria
–
A corporate cafeteria in
Bangalore,
India, December 2003.
Cafeteria
–
The dining hall in
Currier House of
Harvard College, August 2005.
Cafeteria
–
Childs Restaurant, Philadelphia, PA, circa 1908
Cafeteria
–
Divided trays from an East German canteen in the late 1960s.
29.
FDACS
–
The Florida Department of Agriculture and Consumer Services is an executive department of the government of Florida. The Commissioner of Agriculture is the head of the department, the current commissioner is Adam Putnam. The Florida Constitution of 1868 provided for the creation of the Office of Commissioner of Immigration, the Florida Constitution was amended in 1871 to consolidate the offices of Surveyor General and Commissioner of Immigration as the new Commissioner of Lands and Immigration. In 1885, the Constitution was revised and the Commissioner of Lands, the duties of the Commissioner of Agriculture were revised to include supervision of the state prisons. The Agricultural Services Reorganization Act was passed in 1959 and became effective January 15,1961 and this state law abolished some independent boards and bureaus, which were assigned to the Department of Agricultures divisions. These included, Administration, Animal Industry, Dairy Industry, Fruit and Vegetable Inspection, Marketing, Plant Industry, Inspection, the State Chemist, a position that existed since 1891, was moved to the new Division of Chemistry. The Legislature created the Office of Consumer Services in 1967, the Executive Reorganization Act of 1969 renamed the Office of Consumer Services the Division of Consumer Services and the Board of Forestry the Division of Forestry. The Department of Agriculture was renamed the Department of Agriculture and Consumer Services, the Department of Agriculture and Consumer Services is headed by the Commissioner, who is elected statewide to a four-year term. The Commissioner is assisted in managing the Department by a Chief of Staff, the Department is organizated into twelve programatic Divisions and one support Division, each headed by a Division Director. Each Division is subdivided into Bureaus, with each headed by a Bureau Chief, the Bureaus are further subdivided into Sections
FDACS
–
FDACS Florida Forest Service manages Florida's 35
State Forests, including
Lake George State Forest in
Volusia County.
FDACS
–
State Seal of Florida
FDACS
–
Florida scales used in trade, as this hospital cafeteria checkout scale in
Port Charlotte, are inspected for accuracy by the Division of Standards' Bureau of Weights and Measures.
FDACS
–
The Florida Department of Agriculture and Consumer Services building in
Tallahassee.
30.
National Institute of Standards and Technology
–
The National Institute of Standards and Technology is a measurement standards laboratory, and a non-regulatory agency of the United States Department of Commerce. Its mission is to promote innovation and industrial competitiveness, in 1821, John Quincy Adams had declared Weights and measures may be ranked among the necessities of life to every individual of human society. From 1830 until 1901, the role of overseeing weights and measures was carried out by the Office of Standard Weights and Measures, president Theodore Roosevelt appointed Samuel W. Stratton as the first director. The budget for the first year of operation was $40,000, a laboratory site was constructed in Washington, DC, and instruments were acquired from the national physical laboratories of Europe. In addition to weights and measures, the Bureau developed instruments for electrical units, in 1905 a meeting was called that would be the first National Conference on Weights and Measures. Quality standards were developed for products including some types of clothing, automobile brake systems and headlamps, antifreeze, during World War I, the Bureau worked on multiple problems related to war production, even operating its own facility to produce optical glass when European supplies were cut off. Between the wars, Harry Diamond of the Bureau developed a blind approach radio aircraft landing system, in 1948, financed by the Air Force, the Bureau began design and construction of SEAC, the Standards Eastern Automatic Computer. The computer went into operation in May 1950 using a combination of vacuum tubes, about the same time the Standards Western Automatic Computer, was built at the Los Angeles office of the NBS and used for research there. A mobile version, DYSEAC, was built for the Signal Corps in 1954, due to a changing mission, the National Bureau of Standards became the National Institute of Standards and Technology in 1988. Following 9/11, NIST conducted the investigation into the collapse of the World Trade Center buildings. NIST had a budget for fiscal year 2007 of about $843.3 million. NISTs 2009 budget was $992 million, and it also received $610 million as part of the American Recovery, NIST employs about 2,900 scientists, engineers, technicians, and support and administrative personnel. About 1,800 NIST associates complement the staff, in addition, NIST partners with 1,400 manufacturing specialists and staff at nearly 350 affiliated centers around the country. NIST publishes the Handbook 44 that provides the Specifications, tolerances, the Congress of 1866 made use of the metric system in commerce a legally protected activity through the passage of Metric Act of 1866. NIST is headquartered in Gaithersburg, Maryland, and operates a facility in Boulder, nISTs activities are organized into laboratory programs and extramural programs. Effective October 1,2010, NIST was realigned by reducing the number of NIST laboratory units from ten to six, nISTs Boulder laboratories are best known for NIST‑F1, which houses an atomic clock. NIST‑F1 serves as the source of the official time. NIST also operates a neutron science user facility, the NIST Center for Neutron Research, the NCNR provides scientists access to a variety of neutron scattering instruments, which they use in many research fields
National Institute of Standards and Technology
–
Chart of NBS activities, 1915.
National Institute of Standards and Technology
–
A spectrometer in use at the NBS in 1948.
National Institute of Standards and Technology
–
Advanced Measurement Laboratory Complex in Gaithersburg
National Institute of Standards and Technology
–
Boulder Laboratories
31.
Gravitational force
–
Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies. Since energy and mass are equivalent, all forms of energy, including light, on Earth, gravity gives weight to physical objects and causes the ocean tides. Gravity has a range, although its effects become increasingly weaker on farther objects. The most extreme example of this curvature of spacetime is a hole, from which nothing can escape once past its event horizon. More gravity results in time dilation, where time lapses more slowly at a lower gravitational potential. Gravity is the weakest of the four fundamental interactions of nature, the gravitational attraction is approximately 1038 times weaker than the strong force,1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, gravity has an influence on the behavior of subatomic particles. On the other hand, gravity is the dominant interaction at the macroscopic scale, for this reason, in part, pursuit of a theory of everything, the merging of the general theory of relativity and quantum mechanics into quantum gravity, has become an area of research. While the modern European thinkers are credited with development of gravitational theory, some of the earliest descriptions came from early mathematician-astronomers, such as Aryabhata, who had identified the force of gravity to explain why objects do not fall out when the Earth rotates. Later, the works of Brahmagupta referred to the presence of force, described it as an attractive force. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and this was a major departure from Aristotles belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass may fall slower in an atmosphere, galileos work set the stage for the formulation of Newtons theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newtons theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the position of the planet. A discrepancy in Mercurys orbit pointed out flaws in Newtons theory, the issue was resolved in 1915 by Albert Einsteins new theory of general relativity, which accounted for the small discrepancy in Mercurys orbit. The simplest way to test the equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the rate when other forces are negligible
Gravitational force
–
Sir Isaac Newton, an English physicist who lived from 1642 to 1727
Gravitational force
–
Two-dimensional analogy of spacetime distortion generated by the mass of an object. Matter changes the geometry of spacetime, this (curved) geometry being interpreted as gravity. White lines do not represent the curvature of space but instead represent the
coordinate system imposed on the curved spacetime, which would be
rectilinear in a flat spacetime.
Gravitational force
–
Ball falling freely under gravity. See text for description.
Gravitational force
–
Gravity acts on stars that conform our
Milky Way.
32.
Buoyancy
–
In science, buoyancy or upthrust, is an upward force exerted by a fluid that opposes the weight of an immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid, thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object and this pressure difference results in a net upwards force on the object. For this reason, an object whose density is greater than that of the fluid in which it is submerged tends to sink, If the object is either less dense than the liquid or is shaped appropriately, the force can keep the object afloat. This can occur only in a reference frame, which either has a gravitational field or is accelerating due to a force other than gravity defining a downward direction. In a situation of fluid statics, the net upward force is equal to the magnitude of the weight of fluid displaced by the body. The center of buoyancy of an object is the centroid of the volume of fluid. Archimedes principle is named after Archimedes of Syracuse, who first discovered this law in 212 B. C, more tersely, Buoyancy = weight of displaced fluid. The weight of the fluid is directly proportional to the volume of the displaced fluid. Thus, among completely submerged objects with equal masses, objects with greater volume have greater buoyancy and this is also known as upthrust. Suppose a rocks weight is measured as 10 newtons when suspended by a string in a vacuum with gravity acting upon it, suppose that when the rock is lowered into water, it displaces water of weight 3 newtons. The force it exerts on the string from which it hangs would be 10 newtons minus the 3 newtons of buoyancy force,10 −3 =7 newtons. Buoyancy reduces the apparent weight of objects that have sunk completely to the sea floor and it is generally easier to lift an object up through the water than it is to pull it out of the water. The density of the object relative to the density of the fluid can easily be calculated without measuring any volumes. Density of object density of fluid = weight weight − apparent immersed weight Example, If you drop wood into water, Example, A helium balloon in a moving car. During a period of increasing speed, the air mass inside the car moves in the direction opposite to the cars acceleration, the balloon is also pulled this way. However, because the balloon is buoyant relative to the air, it ends up being pushed out of the way, If the car slows down, the same balloon will begin to drift backward. For the same reason, as the car goes round a curve and this is the equation to calculate the pressure inside a fluid in equilibrium
Buoyancy
–
A metallic coin (one British
pound coin) floats in
mercury due to the buoyancy force upon it and appears to float higher because of the surface tension of the mercury.
Buoyancy
–
The forces at work in buoyancy. Note that the object is floating because the upward force of buoyancy is equal to the downward force of
gravity.
33.
Friction
–
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction, Dry friction resists relative lateral motion of two surfaces in contact. Dry friction is subdivided into static friction between non-moving surfaces, and kinetic friction between moving surfaces, fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces, skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. Internal friction is the force resisting motion between the making up a solid material while it undergoes deformation. When surfaces in contact move relative to other, the friction between the two surfaces converts kinetic energy into thermal energy. This property can have consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Kinetic energy is converted to thermal energy whenever motion with friction occurs, another important consequence of many types of friction can be wear, which may lead to performance degradation and/or damage to components. Friction is a component of the science of tribology, Friction is not itself a fundamental force. Dry friction arises from a combination of adhesion, surface roughness, surface deformation. The complexity of interactions makes the calculation of friction from first principles impractical and necessitates the use of empirical methods for analysis. Friction is a non-conservative force - work done against friction is path dependent, in the presence of friction, some energy is always lost in the form of heat. Thus mechanical energy is not conserved, the Greeks, including Aristotle, Vitruvius, and Pliny the Elder, were interested in the cause and mitigation of friction. They were aware of differences between static and kinetic friction with Themistius stating in 350 A. D. that it is easier to further the motion of a moving body than to move a body at rest. The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, a pioneer in tribology and these laws were rediscovered by Guillaume Amontons in 1699. Amontons presented the nature of friction in terms of surface irregularities, the understanding of friction was further developed by Charles-Augustin de Coulomb. Coulomb further considered the influence of sliding velocity, temperature and humidity, the distinction between static and dynamic friction is made in Coulombs friction law, although this distinction was already drawn by Johann Andreas von Segner in 1758. Leslie was equally skeptical about the role of adhesion proposed by Desaguliers, in Leslies view, friction should be seen as a time-dependent process of flattening, pressing down asperities, which creates new obstacles in what were cavities before
Friction
–
When the mass is not moving, the object experiences static friction. The friction increases as the applied force increases until the block moves. After the block moves, it experiences kinetic friction, which is less than the maximum static friction.
34.
Thermal expansion
–
Thermal expansion is the tendency of matter to change in shape, area, and volume in response to a change in temperature. Temperature is a function of the average molecular kinetic energy of a substance. When a substance is heated, the energy of its molecules increases. Thus, the molecules begin vibrating/moving more and usually maintain an average separation. Materials which contract with increasing temperature are unusual, this effect is limited in size, the degree of expansion divided by the change in temperature is called the materials coefficient of thermal expansion and generally varies with temperature. If an equation of state is available, it can be used to predict the values of the expansion at all the required temperatures and pressures. A number of contract on heating within certain temperature ranges. For example, the coefficient of expansion of water drops to zero as it is cooled to 3. Also, fairly pure silicon has a coefficient of thermal expansion for temperatures between about 18 and 120 Kelvin. Unlike gases or liquids, solid materials tend to keep their shape when undergoing thermal expansion, in general, liquids expand slightly more than solids. The thermal expansion of glasses is higher compared to that of crystals, at the glass transition temperature, rearrangements that occur in an amorphous material lead to characteristic discontinuities of coefficient of thermal expansion and specific heat. These discontinuities allow detection of the transition temperature where a supercooled liquid transforms to a glass. Absorption or desorption of water can change the size of common materials. Common plastics exposed to water can, in the long term, the coefficient of thermal expansion describes how the size of an object changes with a change in temperature. Specifically, it measures the change in size per degree change in temperature at a constant pressure. Several types of coefficients have been developed, volumetric, area, which is used depends on the particular application and which dimensions are considered important. For solids, one might only be concerned with the change along a length, the volumetric thermal expansion coefficient is the most basic thermal expansion coefficient, and the most relevant for fluids. In general, substances expand or contract when their temperature changes, substances that expand at the same rate in every direction are called isotropic
Thermal expansion
–
Expansion joint in a
road bridge used to avoid damage from thermal expansion.
Thermal expansion
–
Thermal expansion of long continuous sections of rail tracks is the driving force for
rail buckling. This phenomenon resulted in 190 train derailments during 1998–2002 in the US alone.
Thermal expansion
–
Drinking glass with fracture due to uneven thermal expansion after pouring of hot liquid into the otherwise cool glass
35.
Magnetic fields
–
A magnetic field is the magnetic effect of electric currents and magnetic materials. The magnetic field at any point is specified by both a direction and a magnitude, as such it is represented by a vector field. The term is used for two distinct but closely related fields denoted by the symbols B and H, where H is measured in units of amperes per meter in the SI, B is measured in teslas and newtons per meter per ampere in the SI. B is most commonly defined in terms of the Lorentz force it exerts on moving electric charges, Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. In quantum physics, the field is quantized and electromagnetic interactions result from the exchange of photons. Magnetic fields are used throughout modern technology, particularly in electrical engineering. The Earth produces its own field, which is important in navigation. Rotating magnetic fields are used in electric motors and generators. Magnetic forces give information about the carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits, noting that the resulting field lines crossed at two points he named those points poles in analogy to Earths poles. He also clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them, almost three centuries later, William Gilbert of Colchester replicated Petrus Peregrinus work and was the first to state explicitly that Earth is a magnet. Published in 1600, Gilberts work, De Magnete, helped to establish magnetism as a science, in 1750, John Michell stated that magnetic poles attract and repel in accordance with an inverse square law. Charles-Augustin de Coulomb experimentally verified this in 1785 and stated explicitly that the north and south poles cannot be separated, building on this force between poles, Siméon Denis Poisson created the first successful model of the magnetic field, which he presented in 1824. In this model, a magnetic H-field is produced by magnetic poles, three discoveries challenged this foundation of magnetism, though. First, in 1819, Hans Christian Ørsted discovered that an electric current generates a magnetic field encircling it, then in 1820, André-Marie Ampère showed that parallel wires having currents in the same direction attract one another. Finally, Jean-Baptiste Biot and Félix Savart discovered the Biot–Savart law in 1820, extending these experiments, Ampère published his own successful model of magnetism in 1825. This has the benefit of explaining why magnetic charge can not be isolated. Also in this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism, in 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field
Magnetic fields
–
One of the first drawings of a magnetic field, by
René Descartes, 1644. It illustrated his theory that magnetism was caused by the circulation of tiny helical particles, "threaded parts", through threaded pores in magnets.
Magnetic fields
–
Magnetic field of an ideal cylindrical
magnet with its axis of symmetry inside the image plane. The magnetic field is represented by
magnetic field lines, which show the direction of the field at different points.
Magnetic fields
–
Hans Christian Ørsted, Der Geist in der Natur, 1854
36.
Electrostatic field
–
An electric field is a vector field that associates to each point in space the Coulomb force that would be experienced per unit of electric charge, by an infinitesimal test charge at that point. Electric fields are created by electric charges and can be induced by time-varying magnetic fields, the electric field combines with the magnetic field to form the electromagnetic field. The electric field, E, at a point is defined as the force, F. A particle of charge q would be subject to a force F = q E and its SI units are newtons per coulomb or, equivalently, volts per metre, which in terms of SI base units are kg⋅m⋅s−3⋅A−1. Electric fields are caused by electric charges or varying magnetic fields, in the special case of a steady state, the Maxwell-Faraday inductive effect disappears. The resulting two equations, taken together, are equivalent to Coulombs law, written as E =14 π ε0 ∫ d r ′ ρ r − r ′ | r − r ′ |3 for a charge density ρ. Notice that ε0, the permittivity of vacuum, must be substituted if charges are considered in non-empty media, the equations of electromagnetism are best described in a continuous description. A charge q located at r 0 can be described mathematically as a charge density ρ = q δ, conversely, a charge distribution can be approximated by many small point charges. Electric fields satisfy the principle, because Maxwells equations are linear. This principle is useful to calculate the field created by point charges. Q n are stationary in space at r 1, r 2, in that case, Coulombs law fully describes the field. If a system is static, such that magnetic fields are not time-varying, then by Faradays law, in this case, one can define an electric potential, that is, a function Φ such that E = − ∇ Φ. This is analogous to the gravitational potential, Coulombs law, which describes the interaction of electric charges, F = q = q E is similar to Newtons law of universal gravitation, F = m = m g. This suggests similarities between the electric field E and the gravitational field g, or their associated potentials, mass is sometimes called gravitational charge because of that similarity. Electrostatic and gravitational forces both are central, conservative and obey an inverse-square law, a uniform field is one in which the electric field is constant at every point. It can be approximated by placing two conducting plates parallel to other and maintaining a voltage between them, it is only an approximation because of boundary effects. Assuming infinite planes, the magnitude of the electric field E is, electrodynamic fields are E-fields which do change with time, for instance when charges are in motion. The electric field cannot be described independently of the field in that case
Electrostatic field
–
Electric field lines emanating from a point positive
electric charge suspended over an infinite sheet of conducting material.
37.
Corrosion
–
Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the dedicated to controlling and stopping corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfur, rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide or salt of the original metal, corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids, many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the surface, such as passivation and chromate conversion. However, some corrosion mechanisms are less visible and less predictable, in a galvanic couple, the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a slower rate. When immersed separately, each metal corrodes at its own rate, what type of metal to use is readily determined by following the galvanic series. For example, zinc is used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the industry and also anywhere water contacts pipes or metal structures. Factors such as size of anode, types of metal. The surface area ratio of the anode and cathode directly affects the corrosion rates of the materials, galvanic corrosion is often prevented by the use of sacrificial anodes. In any given environment, one metal will be more noble or more active than others. Two metals in electrical contact share the same electrons, so that the tug-of-war at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a series and is useful in predicting and understanding corrosion
Corrosion
–
Rust, the most familiar example of corrosion.
Corrosion
–
Volcanic gases have accelerated the corrosion of this abandoned mining machinery.
Corrosion
–
Corrosion on exposed metal.
Corrosion
–
Galvanic corrosion of aluminium. A 5-mm-thick aluminium alloy plate is physically (and hence, electrically) connected to a 10-mm-thick mild steel structural support. Galvanic corrosion occurred on the aluminium plate along the joint with the steel. Perforation of aluminium plate occurred within 2 years.
38.
Condensation
–
Condensation is the change of the physical state of matter from gas phase into liquid phase, and is the reverse of evaporation. The word most often refers to the water cycle and it can also be defined as the change in the state of water vapour to liquid water when in contact with a liquid or solid surface or cloud condensation nuclei within the atmosphere. When the transition happens from the phase into the solid phase directly. A few distinct reversibility scenarios emerge here with respect to the nature of the surface, absorption into the surface of a liquid —is reversible as evaporation. Adsorption onto solid surface at pressures and temperatures higher than the species triple point—also reversible as evaporation, adsorption onto solid surface at pressures and temperatures lower than the species triple point—is reversible as sublimation. Condensation commonly occurs when a vapor is cooled and/or compressed to its limit when the molecular density in the gas phase reaches its maximal threshold. Vapor cooling and compressing equipment that collects condensed liquids is called a condenser, psychrometry measures the rates of condensation through evaporation into the air moisture at various atmospheric pressures and temperatures. Water is the product of its vapor condensation—condensation is the process of such phase conversion, condensation is a crucial component of distillation, an important laboratory and industrial chemistry application. Because condensation is a naturally occurring phenomenon, it can often be used to water in large quantities for human use. Many structures are made solely for the purpose of collecting water from condensation, such as air wells and it is also a crucial process in forming particle tracks in a cloud chamber. In this case, ions produced by an incident particle act as centers for the condensation of the vapor producing the visible cloud trails. Furthermore, condensation is a step in many industrial processes, such as power generation, water desalination, thermal management, refrigeration. Numerous living beings use water made accessible by condensation, a few examples of these are the Australian Thorny Devil, the darkling beetles of the Namibian coast, and the Coast Redwoods of the West Coast of the United States. To alleviate these issues, the air humidity needs to be lowered. This can be done in a number of ways, for example opening windows, turning on extractor fans, using dehumidifiers, drying clothes outside and covering pots and pans whilst cooking. Air conditioning or ventilation systems can be installed that help remove moisture from the air, the amount of water vapour that can be stored in the air can be increased simply by increasing the temperature. However, this can be a double edged sword as most condensation in the home occurs when warm, as the air is cooled, it can no longer hold as much water vapour. This leads to deposition of water on the cool surface and this is very apparent when central heating is used in combination with single glazed windows in winter
Condensation
–
Condensation forming in the low pressure zone above the wing of an aircraft due to
adiabatic expansion
Condensation
–
Condensation on a window during a rain shower.
39.
Evaporation
–
Evaporation is a type of vaporization of a liquid that occurs from the surface of a liquid into a gaseous phase that is not saturated with the evaporating substance. The other type of vaporization is boiling, which is characterized by bubbles of saturated vapor forming in the liquid phase, steam produced in a boiler is another example of evaporation occurring in a saturated vapor phase. Evaporation that occurs directly from the solid phase below the melting point, on average, a fraction of the molecules in a glass of water have enough heat energy to escape from the liquid. The water in the glass will be cooled by the evaporation until an equilibrium is reached where the air supplies the amount of heat removed by the evaporating water, in an enclosed environment the water would evaporate until the air is saturated. With sufficient temperature, the liquid would turn into vapor quickly, when the molecules collide, they transfer energy to each other in varying degrees, based on how they collide. Sometimes the transfer is so one-sided for a molecule near the surface that it ends up with energy to escape. Evaporation is an part of the water cycle. The sun drives evaporation of water from oceans, lakes, moisture in the soil, in hydrology, evaporation and transpiration are collectively termed evapotranspiration. Evaporation of water occurs when the surface of the liquid is exposed, allowing molecules to escape and form water vapor, when only a small proportion of the molecules meet these criteria, the rate of evaporation is low. Since the kinetic energy of a molecule is proportional to its temperature, as the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid decreases. This phenomenon is also called evaporative cooling and this is why evaporating sweat cools the human body. Evaporation also tends to proceed quickly with higher flow rates between the gaseous and liquid phase and in liquids with higher vapor pressure. For example, laundry on a line will dry more rapidly on a windy day than on a still day. Three key parts to evaporation are heat, atmospheric pressure, on a molecular level, there is no strict boundary between the liquid state and the vapor state. Instead, there is a Knudsen layer, where the phase is undetermined, because this layer is only a few molecules thick, at a macroscopic scale a clear phase transition interface cannot be seen. It is just that the process is slower and thus significantly less visible. If evaporation takes place in an area, the escaping molecules accumulate as a vapor above the liquid. Many of the return to the liquid, with returning molecules becoming more frequent as the density
Evaporation
–
Aerosol of microscopic water droplets suspended in the air above a hot tea cup after that water vapor has sufficiently cooled and condensed.
Water vapor is an invisible
gas, but the
clouds of condensed water droplets refract and disperse the sun light and so are visible.
Evaporation
–
Vapor pressure of water vs. temperature. 760
Torr = 1
atm.
40.
Convection
–
Convection is the movement of groups of molecules within fluids such as liquids or gases, and within rheids. Convection takes place through advection, diffusion or both, convection cannot take place in solids because neither bulk current flows nor significant diffusion can take place in solids. Diffusion of heat can take place in solids, but that is called heat conduction, convective heat transfer is one of the major types of heat transfer, and convection is also a major mode of mass transfer in fluids. In the context of heat and mass transfer, the convection is used to refer to the sum of advective and diffusive transfer. In common use the term convection may refer loosely to heat transfer by convection, as opposed to mass transfer by convection, sometimes convection is even used to refer specifically to free heat convection as opposed to forced heat convection. However, in mechanics the correct use of the word is the general sense, convection can be qualified in terms of being natural, forced, gravitational, granular, or thermomagnetic. It may also be said to be due to combustion, capillary action, or Marangoni, heat transfer by natural convection plays a role in the structure of Earths atmosphere, its oceans, and its mantle. Discrete convective cells in the atmosphere can be seen as clouds, natural convection also plays a role in stellar physics. The word convection may have different but related usages in different scientific or engineering contexts or applications. The broader sense is in fluid mechanics, where convection refers to the motion of fluid regardless of cause, however, in thermodynamics convection often refers specifically to heat transfer by convection. Additionally, convection includes fluid movement both by bulk motion and by the motion of individual particles, however, in some cases, convection is taken to mean only advective phenomena. Convection occurs on a scale in atmospheres, oceans, planetary mantles. Fluid movement during convection may be slow, or it may be obvious and rapid. On astronomical scales, convection of gas and dust is thought to occur in the disks of black holes. Convective heat transfer is a mechanism of heat transfer occurring because of bulk motion of fluids, heat is the entity of interest being advected, and diffused. Heat is transferred by convection in numerous examples of naturally occurring fluid flow, such as, wind, oceanic currents, convection is also used in engineering practices of homes, industrial processes, cooling of equipment, etc. The rate of heat transfer may be improved by the use of a heat sink. For instance, a typical computer CPU will have a fan to ensure its operating temperature is kept within tolerable limits
Convection
–
A heat sink provides a large surface area for convection to efficiently carry away heat.
Convection
–
Idealised depiction of the global circulation on Earth
Convection
–
Stages of a thunderstorm's life.
Convection
–
An illustration of the structure of the
Sun and a
red giant star, showing their convective zones. These are the granular zones in the outer layers of these stars.
41.
Balance (ability)
–
In biomechanics, balance is an ability to maintain the line of gravity of a body within the base of support with minimal postural sway. Sway is the movement of the centre of gravity even when a person is standing still. A certain amount of sway is essential and inevitable due to small perturbations within the body or from external triggers, an increase in sway is not necessarily an indicator of dysfunctional balance so much as it is an indicator of decreased sensorimotor control. Maintaining balance requires coordination of input from sensory systems including the vestibular, somatosensory. There are environmental factors that can balance such as light conditions, floor surface changes, alcohol, drugs. There are balance impairments associated with aging, age-related decline in the ability of the above systems to receive and integrate sensory information contributes to poor balance in older adults. As a result, the elderly are at a risk of falls. In fact, one in three adults aged 65 and over will fall each year, in the case of an individual standing quietly upright, the limit of stability is defined as the amount of postural sway at which balance is lost and corrective action is required. Body sway can occur in all planes of motion, which make it an increasingly difficult ability to rehabilitate, there is strong evidence in research showing that deficits in postural balance is related to the control of medial-lateral stability and an increased risk of falling. To remain balanced, a person standing must be able to keep the vertical projection of their center of mass within their base of support, ankle sprains are one of the most frequently occurring injuries among athletes and physically active people. The most common residual disability post ankle sprain is instability along with body sway and it is found that nearly 40% of patients with ankle sprains suffer from instability and an increase in body sway. Injury to the causes an proprioceptive deficit and impaired postural control. Individuals with muscular weakness, occult instability, and decreased postural control are more susceptible to injury than those with better postural control. Balance can be affected in individuals with neurological conditions. Patients who suffer a stroke or a spinal cord injury for example and it has also been determined that impaired balance is strongly associated with future function and recovery in some cases, particularly in stroke patients. Additionally, balance problems have been identified as the strongest predictor of falls, another population where balance is severely affected is Parkinsons disease patients. Balance can also be affected in a normal population through fatigue in the musculature surrounding the ankles, knees. Studies have found, however, that muscle fatigue around the hips and it is thought that muscle fatigue leads to a decreased ability to contract with the correct amount of force or accuracy
Balance (ability)
–
A woman demonstrating the ability to balance
Balance (ability)
–
A
waiter balancing wine glasses
Balance (ability)
–
Balance
Balance (ability)
–
Balance Training
42.
Steelyard balance
–
A steelyard balance, steelyard, or stilyard is a straight-beam balance with arms of unequal length. It incorporates a counterweight which slides along the arm to counterbalance the load. A steelyard is also known as a Roman steelyard or Roman balance, the steelyard comprises a balance beam which is suspended from a pivot which is very close to one end of the beam. The two parts of the beam which flank the pivot are the arms, the arm from which the object to be weighed is hung is short and is located close to the pivot point. The Latin name statera comes from the Ancient Greek στατήρ, Roman and Chinese steelyards were independently invented around 200 BC. Steelyards dating from AD100 to 400 have been unearthed in Great Britain, large steelyard balances, both public and private, were a common feature in agricultural areas in England from the eighteenth century forward. An example of a public cart steelyard remains at Soham, Cambridgeshire and another is to be seen at Woodbridge, steelyards of different sizes have been used to weigh loads ranging from ounces to tons. A small steelyard could be a foot or less in length and thus used as a portable device that merchants. In other cases a steelyard could be several feet long and used to weigh sacks of flour, even larger steelyards were three stories tall and used to weigh fully laden horse-drawn carts. A Scandinavian steelyard is a variant which consists of a bar with a weight attached to one end, a movable pivot point. Once the object to be weighed is attached to its end of the bar, the pivot point, the bar can be calibrated so that the objects weight can be read off directly from the position of the pivot. This type is known in Sweden, Denmark and Norway. C. E, Roman steelyards unearthed in Britain A three-story steelyard
Steelyard balance
–
Roman steelyard from
Pompeii
Steelyard balance
–
A 19th-century steelyard.
43.
Beam (structure)
–
A beam is a structural element that primarily resists loads applied laterally to the beams axis. Its mode of deflection is primarily by bending, the loads applied to the beam result in reaction forces at the beams support points. The total effect of all the acting on the beam is to produce shear forces and bending moments within the beam. Beams are characterized by their manner of support, profile, length, historically beams were squared timbers but are also metal, stone, or combinations of wood and metal such as a flitch beam. Beams generally carry vertical gravitational forces but can also be used to carry horizontal loads, the loads carried by a beam are transferred to columns, walls, or girders, which then transfer the force to adjacent structural compression members. In light frame construction joists may rest on beams, in carpentry a beam is called a plate as in a sill plate or wall plate, beam as in a summer beam or dragon beam. In engineering, beams are of types, Simply supported - a beam supported on the ends which are free to rotate and have no moment resistance. Fixed - a beam supported on both ends and restrained from rotation, over hanging - a simple beam extending beyond its support on one end. Double overhanging - a simple beam with both ends extending beyond its supports on both ends, continuous - a beam extending over more than two supports. Cantilever - a projecting beam fixed only at one end, trussed - a beam strengthened by adding a cable or rod to form a truss. In the beam equation I is used to represent the moment of area. It is commonly known as the moment of inertia, and is the sum, about the axis, of dA*r^2, where r is the distance from the neutral axis. Therefore, it not just how much area the beam section has overall. The greater I is, the stiffer the beam in bending, internally, beams experience compressive, tensile and shear stresses as a result of the loads applied to them. Above the supports, the beam is exposed to shear stress, there are some reinforced concrete beams in which the concrete is entirely in compression with tensile forces taken by steel tendons. These beams are known as prestressed concrete beams, and are fabricated to produce a more than the expected tension under loading conditions. High strength steel tendons are stretched while the beam is cast over them, then, when the concrete has cured, the tendons are slowly released and the beam is immediately under eccentric axial loads. This eccentric loading creates a moment, and, in turn
Beam (structure)
–
A
statically determinate beam, bending (sagging) under a uniformly distributed load
44.
Mechanical equilibrium
–
In classical mechanics, a particle is in mechanical equilibrium if the net force on that particle is zero. By extension, a system made up of many parts is in mechanical equilibrium if the net force on each of its individual parts is zero. In addition to defining mechanical equilibrium in terms of force, there are alternative definitions for mechanical equilibrium which are all mathematically equivalent. In terms of momentum, a system is in if the momentum of its parts is all constant. In terms of velocity, the system is in equilibrium if velocity is constant, in a rotational mechanical equilibrium the angular momentum of the object is conserved and the net torque is zero. More generally in conservative systems, equilibrium is established at a point in space where the gradient of the potential energy with respect to the generalized coordinates is zero. If a particle in equilibrium has zero velocity, that particle is in static equilibrium, since all particles in equilibrium have constant velocity, it is always possible to find an inertial reference frame in which the particle is stationary with respect to the frame. An important property of systems at mechanical equilibrium is their stability, if we have a function which describes the systems potential energy, we can determine the systems equilibria using calculus. A system is in equilibrium at the critical points of the function describing the systems potential energy. We can locate these points using the fact that the derivative of the function is zero at these points, if the system is displaced an arbitrarily small distance from the equilibrium state, the forces of the system cause it to move even farther away. Second derivative >0, The potential energy is at a local minimum, the response to a small perturbation is forces that tend to restore the equilibrium. If more than one equilibrium state is possible for a system. Second derivative =0 or does not exist, The state is neutral to the lowest order, to investigate the precise stability of the system, higher order derivatives must be examined. In a truly neutral state the energy does not vary and the state of equilibrium has a finite width and this is sometimes referred to as state that is marginally stable or in a state of indifference. Generally an equilibrium is only referred to as if it is stable in all directions. Sometimes there is not enough information about the acting on a body to determine if it is in equilibrium or not. This makes it an indeterminate system. The special case of mechanical equilibrium of an object is static equilibrium
Mechanical equilibrium
–
Force diagram showing the
forces acting on an object at rest on a surface. The
normal force N is equal and opposite to the
gravitational force mg so the net force is zero. Consequently the object is in a state of static mechanical equilibrium.
45.
Gravity of Earth
–
The gravity of Earth, which is denoted by g, refers to the acceleration that is imparted to objects due to the distribution of mass within the Earth. In SI units this acceleration is measured in metres per second squared or equivalently in newtons per kilogram and this quantity is sometimes referred to informally as little g. The precise strength of Earths gravity varies depending on location, the nominal average value at the Earths surface, known as standard gravity is, by definition,9.80665 m/s2. This quantity is denoted variously as gn, ge, g0, gee, the weight of an object on the Earths surface is the downwards force on that object, given by Newtons second law of motion, or F = ma. Gravitational acceleration contributes to the acceleration, but other factors, such as the rotation of the Earth, also contribute. The Earth is not spherically symmetric, but is slightly flatter at the poles while bulging at the Equator, there are consequently slight deviations in both the magnitude and direction of gravity across its surface. The net force as measured by a scale and plumb bob is called effective gravity or apparent gravity, effective gravity includes other factors that affect the net force. These factors vary and include such as centrifugal force at the surface from the Earths rotation. Effective gravity on the Earths surface varies by around 0. 7%, in large cities, it ranges from 9.766 in Kuala Lumpur, Mexico City, and Singapore to 9.825 in Oslo and Helsinki. The surface of the Earth is rotating, so it is not a frame of reference. At latitudes nearer the Equator, the centrifugal force produced by Earths rotation is larger than at polar latitudes. This counteracts the Earths gravity to a small degree – up to a maximum of 0. 3% at the Equator –, the same two factors influence the direction of the effective gravity. Gravity decreases with altitude as one rises above the Earths surface because greater altitude means greater distance from the Earths centre, all other things being equal, an increase in altitude from sea level to 9,000 metres causes a weight decrease of about 0. 29%. It is a misconception that astronauts in orbit are weightless because they have flown high enough to escape the Earths gravity. In fact, at an altitude of 400 kilometres, equivalent to an orbit of the Space Shuttle. Weightlessness actually occurs because orbiting objects are in free-fall, the effect of ground elevation depends on the density of the ground. A person flying at 30000 ft above sea level over mountains will feel more gravity than someone at the same elevation, however, a person standing on the earths surface feels less gravity when the elevation is higher. The following formula approximates the Earths gravity variation with altitude, g h = g 02 Where gh is the acceleration at height h above sea level
Gravity of Earth
–
Earth's gravity measured by NASA's
GRACE mission, showing deviations from the
theoretical gravity of an idealized smooth Earth, the so-called
earth ellipsoid. Red shows the areas where gravity is stronger than the smooth, standard value, and blue reveals areas where gravity is weaker. (
Animated version.)
Gravity of Earth
–
Earth's radial density distribution according to the Preliminary Reference Earth Model (PREM).
46.
Units of mass
–
In physics, mass is a property of a physical body. It is the measure of a resistance to acceleration when a net force is applied. It also determines the strength of its gravitational attraction to other bodies. The basic SI unit of mass is the kilogram, Mass is not the same as weight, even though mass is often determined by measuring the objects weight using a spring scale, rather than comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity and this is because weight is a force, while mass is the property that determines the strength of this force. In Newtonian physics, mass can be generalized as the amount of matter in an object, however, at very high speeds, special relativity postulates that energy is an additional source of mass. Thus, any body having mass has an equivalent amount of energy. In addition, matter is a defined term in science. There are several distinct phenomena which can be used to measure mass, active gravitational mass measures the gravitational force exerted by an object. Passive gravitational mass measures the force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force, according to Newtons second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A bodys mass also determines the degree to which it generates or is affected by a gravitational field and this is sometimes referred to as gravitational mass. The standard International System of Units unit of mass is the kilogram, the kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. Then in 1889, the kilogram was redefined as the mass of the prototype kilogram. As of January 2013, there are proposals for redefining the kilogram yet again. In this context, the mass has units of eV/c2, the electronvolt and its multiples, such as the MeV, are commonly used in particle physics. The atomic mass unit is 1/12 of the mass of a carbon-12 atom, the atomic mass unit is convenient for expressing the masses of atoms and molecules. Outside the SI system, other units of mass include, the slug is an Imperial unit of mass, the pound is a unit of both mass and force, used mainly in the United States
Units of mass
–
Depiction of early
balance scales in the
Papyrus of Hunefer (dated to the
19th dynasty, ca. 1285 BC). The scene shows
Anubis weighing the heart of Hunefer.
Units of mass
–
The kilogram is one of the seven
SI base units and one of three which is defined ad hoc (i.e. without reference to another base unit).
Units of mass
–
Galileo Galilei (1636)
Units of mass
–
Distance traveled by a freely falling ball is proportional to the square of the elapsed time
47.
Gram
–
The gram is a metric system unit of mass. Originally defined as the weight of a volume of pure water equal to the cube of the hundredth part of a metre. The only unit symbol for gram that is recognised by the International System of Units is g following the numeric value with a space, the SI does not support the use of abbreviations such as gr, gm or Gm. The word gramme was adopted by the French National Convention in its 1795 decree revising the system as replacing the gravet introduced in 1793. Its definition remained that of the weight of a centimetre of water. French gramme was taken from the Late Latin term gramma and this word, ultimately from Greek γράμμα letter had adopted a specialised meaning in Late Antiquity of one twenty-fourth part of an ounce, corresponding to about 1.14 grams. This use of the term is found in the carmen de ponderibus et mensuris composed around 400 AD, the gram was the fundamental unit of mass in the 19th-century centimetre–gram–second system of units. The gram is today the most widely used unit of measurement for non-liquid ingredients in cooking and grocery shopping worldwide. 1 gram =15.4323583529 grains 1 grain =0.06479891 grams 1 avoirdupois ounce =28.349523125 grams 1 troy ounce =31.1034768 grams 100 grams =3.527396195 ounces 1 gram =5 carats 1 gram =8. 1 gram is roughly equal to 1 small paper clip or pen cap, the Japanese 1 yen coin has a mass of one gram. Conversion of units Duella Gold gram Orders of magnitude Gram at Encyclopædia Britannica
Gram
–
The mass of this pen cap is about 1 gram
48.
Accuracy and precision
–
Precision is a description of random errors, a measure of statistical variability. The two concepts are independent of other, so a particular set of data can be said to be either accurate, or precise. In the fields of science, engineering and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantitys true value. The precision of a measurement system, related to reproducibility and repeatability, is the degree to which repeated measurements under unchanged conditions show the same results. Although the two words precision and accuracy can be synonymous in colloquial use, they are contrasted in the context of the scientific method. A measurement system can be accurate but not precise, precise but not accurate, neither, for example, if an experiment contains a systematic error, then increasing the sample size generally increases precision but does not improve accuracy. The result would be a consistent yet inaccurate string of results from the flawed experiment, eliminating the systematic error improves accuracy but does not change precision. A measurement system is considered if it is both accurate and precise. Related terms include bias and error, the terminology is also applied to indirect measurements—that is, values obtained by a computational procedure from observed data. Statistical literature prefers to use the terms bias and variability instead of accuracy and precision, bias is the amount of inaccuracy and variability is the amount of imprecision. In military terms, accuracy refers primarily to the accuracy of fire, ideally a measurement device is both accurate and precise, with measurements all close to and tightly clustered around the true value. The accuracy and precision of a measurement process is established by repeatedly measuring some traceable reference standard. Such standards are defined in the International System of Units and maintained by national organizations such as the National Institute of Standards. This also applies when measurements are repeated and averaged, further, the central limit theorem shows that the probability distribution of the averaged measurements will be closer to a normal distribution than that of individual measurements. With regard to accuracy we can distinguish, the difference between the mean of the measurements and the value, the bias. Establishing and correcting for bias is necessary for calibration, the combined effect of that and precision. A common convention in science and engineering is to express accuracy and/or precision implicitly by means of significant figures, here, when not explicitly stated, the margin of error is understood to be one-half the value of the last significant place. For instance, a recording of 843.6 m, or 843.0 m, or 800.0 m would imply a margin of 0.05 m, while a recording of 8,436 m would imply a margin of error of 0.5 m
Accuracy and precision
–
Accuracy is the proximity of measurement results to the true value; precision, the repeatability, or reproducibility of the measurement
49.
Fulcrum (mechanics)
–
A lever is a machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. A lever is a body capable of rotating on a point on itself. On the basis of the location of fulcrum, load and effort and it is one of the six simple machines identified by Renaissance scientists. A lever amplifies an input force to provide an output force. The ratio of the force to the input force is the mechanical advantage of the lever. The word lever entered English about 1300 from Old French, in which the word was levier and this sprang from the stem of the verb lever, meaning to raise. The verb, in turn, goes back to the Latin levare, itself from the adjective levis, the words primary origin is the Proto-Indo-European stem legwh-, meaning light, easy or nimble, among other things. The PIE stem also gave rise to the English word light, the earliest remaining writings regarding levers date from the 3rd century BC and were provided by Archimedes. Give me a place to stand, and I shall move the Earth with it is a remark of Archimedes who formally stated the correct mathematical principle of levers. The distance required to do this might be exemplified in astronomical terms as the distance to the Circinus galaxy - about 9 million light years. It is assumed that in ancient Egypt, constructors used the lever to move, a lever is a beam connected to ground by a hinge, or pivot, called a fulcrum. The ideal lever does not dissipate or store energy, which there is no friction in the hinge or bending in the beam. This is known as the law of the lever, the mechanical advantage of a lever can be determined by considering the balance of moments or torque, T, about the fulcrum. T1 = F1 a, T2 = F2 b where F1 is the force to the lever. The distances a and b are the distances between the forces and the fulcrum. Since the moments of torque must be balanced, T1 = T2, the mechanical advantage of the lever is the ratio of output force to input force, M A = F2 F1 = a b. Levers are classified by the positions of the fulcrum, effort. It is common to call the force the effort and the output force the load or the resistance
Fulcrum (mechanics)
–
Levers can be used to exert a large force over a small distance at one end by exerting only a small force over a greater distance at the other.
Fulcrum (mechanics)
–
This is an engraving from Mechanics Magazine published in London in 1824.
50.
Knife
–
A knife is a tool with a cutting edge or blade, hand-held or otherwise, with most having a handle. Some types of knives are used as utensils, including knives used at the dining table, many types of knives are used as tools, such as the utility knife carried by soldiers, the pocket knife carried by hikers and the hunting knife used by hunters. Knives are also used as a traditional or religious implement, such as the kirpan, some types of knives are used as weapons, such as daggers or switchblades. Some types of knives are used as sports equipment, Knives are also used in agriculture, food harvesting etc. the sickle, the scythe and even the combine harvester are knives. Knife-like tools were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools. Originally made of rock, bone, flint, and obsidian, knives have evolved in construction as technology has, with blades being made from bronze, copper, iron, steel, ceramics, many cultures have their unique version of the knife. Due to its role as humankinds first tool, certain cultures have attached spiritual, most modern-day knives follow either a fixed-blade or a folding construction style, with blade patterns and styles as varied as their makers and countries of origin. The word knife possibly descends from an old Norse word knifr for blade, single-edged knives may have a reverse edge or false edge occupying a section of the spine. These edges are serrated and are used to further enhance function. The handle, used to grip and manipulate the blade safely, may include a tang, Knives are made with partial tangs or full tangs. The handle may include a bolster, a piece of heavy material situated at the front or rear of the handle, the bolster, as its name suggests, is used to mechanically strengthen the knife. Knife blades can be manufactured from a variety of materials, each of which has advantages and disadvantages, carbon steel, an alloy of iron and carbon, can be very sharp. It holds its edge well, and remains easy to sharpen, stainless steel is an alloy of iron, chromium, possibly nickel, and molybdenum, with only a small amount of carbon. It is not able to quite as sharp an edge as carbon steel. High carbon stainless steel is steel with a higher amount of carbon, intended to incorporate the better attributes of carbon steel. High carbon stainless steel blades do not discolor or stain, laminate blades use multiple metals to create a layered sandwich, combining the attributes of both. For example, a harder, more brittle steel may be sandwiched between a layer of softer, tougher, stainless steel to reduce vulnerability to corrosion. In this case, however, the part most affected by corrosion, pattern-welding is similar to laminate construction
Knife
–
A Bowie-class knife of pattern-welded steel
Knife
–
A butter knife resting on a stand
Knife
–
Characteristic parts of a knife
Knife
–
Knife blade mass production
