1.
System of measurement
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A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce, systems of measurement in modern use include the metric system, the imperial system, and United States customary units. The French Revolution gave rise to the system, and this has spread around the world. In most systems, length, mass, and time are base quantities, later science developments showed that either electric charge or electric current could be added to extend the set of base quantities by which many other metrological units could be easily defined. Other quantities, such as power and speed, are derived from the set, for example. Such arrangements were satisfactory in their own contexts, the preference for a more universal and consistent system only gradually spread with the growth of science. Changing a measurement system has substantial financial and cultural costs which must be offset against the advantages to be obtained using a more rational system. However pressure built up, including scientists and engineers for conversion to a more rational. The unifying characteristic is that there was some definition based on some standard, eventually cubits and strides gave way to customary units to met the needs of merchants and scientists. In the metric system and other recent systems, a basic unit is used for each base quantity. Often secondary units are derived from the units by multiplying by powers of ten. Thus the basic unit of length is the metre, a distance of 1.234 m is 1,234 millimetres. Metrication is complete or nearly complete in almost all countries, US customary units are heavily used in the United States and to some degree in Liberia. Traditional Burmese units of measurement are used in Burma, U. S. units are used in limited contexts in Canada due to the large volume of trade, there is also considerable use of Imperial weights and measures, despite de jure Canadian conversion to metric. In the United States, metric units are used almost universally in science, widely in the military, and partially in industry, but customary units predominate in household use. At retail stores, the liter is a used unit for volume, especially on bottles of beverages. Some other standard non-SI units are still in use, such as nautical miles and knots in aviation. Metric systems of units have evolved since the adoption of the first well-defined system in France in 1795, during this evolution the use of these systems has spread throughout the world, first to non-English-speaking countries, and then to English speaking countries
2.
SI derived unit
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The International System of Units specifies a set of seven base units from which all other SI units of measurement are derived. Each of these units is either dimensionless or can be expressed as a product of powers of one or more of the base units. For example, the SI derived unit of area is the metre. The degree Celsius has an unclear status, and is arguably an exception to this rule. The names of SI units are written in lowercase, the symbols for units named after persons, however, are always written with an uppercase initial letter. In addition to the two dimensionless derived units radian and steradian,20 other derived units have special names, some other units such as the hour, litre, tonne, bar and electronvolt are not SI units, but are widely used in conjunction with SI units. Until 1995, the SI classified the radian and the steradian as supplementary units, but this designation was abandoned, International System of Quantities International System of Units International Vocabulary of Metrology Metric prefix Metric system Non-SI units mentioned in the SI Planck units SI base unit I. Mills, Tomislav Cvitas, Klaus Homann, Nikola Kallay, IUPAC, Quantities, Units and Symbols in Physical Chemistry. CS1 maint, Multiple names, authors list
3.
Force
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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
4.
Isaac Newton
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His book Philosophiæ Naturalis Principia Mathematica, first published in 1687, laid the foundations of classical mechanics. Newton also made contributions to optics, and he shares credit with Gottfried Wilhelm Leibniz for developing the infinitesimal calculus. Newtons Principia formulated the laws of motion and universal gravitation that dominated scientists view of the universe for the next three centuries. Newtons work on light was collected in his influential book Opticks. He also formulated a law of cooling, made the first theoretical calculation of the speed of sound. Newton was a fellow of Trinity College and the second Lucasian Professor of Mathematics at the University of Cambridge, politically and personally tied to the Whig party, Newton served two brief terms as Member of Parliament for the University of Cambridge, in 1689–90 and 1701–02. He was knighted by Queen Anne in 1705 and he spent the last three decades of his life in London, serving as Warden and Master of the Royal Mint and his father, also named Isaac Newton, had died three months before. Born prematurely, he was a child, his mother Hannah Ayscough reportedly said that he could have fit inside a quart mug. When Newton was three, his mother remarried and went to live with her new husband, the Reverend Barnabas Smith, leaving her son in the care of his maternal grandmother, Newtons mother had three children from her second marriage. From the age of twelve until he was seventeen, Newton was educated at The Kings School, Grantham which taught Latin and Greek. He was removed from school, and by October 1659, he was to be found at Woolsthorpe-by-Colsterworth, Henry Stokes, master at the Kings School, persuaded his mother to send him back to school so that he might complete his education. Motivated partly by a desire for revenge against a bully, he became the top-ranked student. In June 1661, he was admitted to Trinity College, Cambridge and he started as a subsizar—paying his way by performing valets duties—until he was awarded a scholarship in 1664, which guaranteed him four more years until he would get his M. A. He set down in his notebook a series of Quaestiones about mechanical philosophy as he found it, in 1665, he discovered the generalised binomial theorem and began to develop a mathematical theory that later became calculus. Soon after Newton had obtained his B. A. degree in August 1665, in April 1667, he returned to Cambridge and in October was elected as a fellow of Trinity. Fellows were required to become ordained priests, although this was not enforced in the restoration years, however, by 1675 the issue could not be avoided and by then his unconventional views stood in the way. Nevertheless, Newton managed to avoid it by means of a special permission from Charles II. A and he was elected a Fellow of the Royal Society in 1672. Newtons work has been said to distinctly advance every branch of mathematics then studied and his work on the subject usually referred to as fluxions or calculus, seen in a manuscript of October 1666, is now published among Newtons mathematical papers
5.
Kilogram
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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
6.
Metre
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The metre or meter, is the base unit of length in the International System of Units. The metre is defined as the length of the path travelled by light in a vacuum in 1/299792458 seconds, the metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. In 1799, it was redefined in terms of a metre bar. In 1960, the metre was redefined in terms of a number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition was adopted, the imperial inch is defined as 0.0254 metres. One metre is about 3 3⁄8 inches longer than a yard, Metre is the standard spelling of the metric unit for length in nearly all English-speaking nations except the United States and the Philippines, which use meter. Measuring devices are spelled -meter in all variants of English, the suffix -meter has the same Greek origin as the unit of length. This range of uses is found in Latin, French, English. Thus calls for measurement and moderation. In 1668 the English cleric and philosopher John Wilkins proposed in an essay a decimal-based unit of length, as a result of the French Revolution, the French Academy of Sciences charged a commission with determining a single scale for all measures. In 1668, Wilkins proposed using Christopher Wrens suggestion of defining the metre using a pendulum with a length which produced a half-period of one second, christiaan Huygens had observed that length to be 38 Rijnland inches or 39.26 English inches. This is the equivalent of what is now known to be 997 mm, no official action was taken regarding this suggestion. In the 18th century, there were two approaches to the definition of the unit of length. One favoured Wilkins approach, to define the metre in terms of the length of a pendulum which produced a half-period of one second. The other approach was to define the metre as one ten-millionth of the length of a quadrant along the Earths meridian, that is, the distance from the Equator to the North Pole. This means that the quadrant would have defined as exactly 10000000 metres at that time. To establish a universally accepted foundation for the definition of the metre, more measurements of this meridian were needed. This portion of the meridian, assumed to be the length as the Paris meridian, was to serve as the basis for the length of the half meridian connecting the North Pole with the Equator
7.
Second
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The second is the base unit of time in the International System of Units. It is qualitatively defined as the division of the hour by sixty. SI definition of second is the duration of 9192631770 periods of the corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. Seconds may be measured using a mechanical, electrical or an atomic clock, SI prefixes are combined with the word second to denote subdivisions of the second, e. g. the millisecond, the microsecond, and the nanosecond. Though SI prefixes may also be used to form multiples of the such as kilosecond. The second is also the unit of time in other systems of measurement, the centimetre–gram–second, metre–kilogram–second, metre–tonne–second. Absolute zero implies no movement, and therefore zero external radiation effects, the second thus defined is consistent with the ephemeris second, which was based on astronomical measurements. The realization of the second is described briefly in a special publication from the National Institute of Standards and Technology. 1 international second is equal to, 1⁄60 minute 1⁄3,600 hour 1⁄86,400 day 1⁄31,557,600 Julian year 1⁄, more generally, = 1⁄, the Hellenistic astronomers Hipparchus and Ptolemy subdivided the day into sixty parts. They also used an hour, simple fractions of an hour. No sexagesimal unit of the day was used as an independent unit of time. The modern second is subdivided using decimals - although the third remains in some languages. The earliest clocks to display seconds appeared during the last half of the 16th century, the second became accurately measurable with the development of mechanical clocks keeping mean time, as opposed to the apparent time displayed by sundials. The earliest spring-driven timepiece with a hand which marked seconds is an unsigned clock depicting Orpheus in the Fremersdorf collection. During the 3rd quarter of the 16th century, Taqi al-Din built a clock with marks every 1/5 minute, in 1579, Jost Bürgi built a clock for William of Hesse that marked seconds. In 1581, Tycho Brahe redesigned clocks that displayed minutes at his observatory so they also displayed seconds, however, they were not yet accurate enough for seconds. In 1587, Tycho complained that his four clocks disagreed by plus or minus four seconds, in 1670, London clockmaker William Clement added this seconds pendulum to the original pendulum clock of Christiaan Huygens. From 1670 to 1680, Clement made many improvements to his clock and this clock used an anchor escapement mechanism with a seconds pendulum to display seconds in a small subdial
8.
International System of Units
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The International System of Units is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, the system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as the result of an initiative began in 1948. It is based on the system of units rather than any variant of the centimetre-gram-second system. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems, the International System of Units has been adopted by most developed countries, however, the adoption has not been universal in all English-speaking countries. The metric system was first implemented during the French Revolution with just the metre and kilogram as standards of length, in the 1830s Carl Friedrich Gauss laid the foundations for a coherent system based on length, mass, and time. In the 1860s a group working under the auspices of the British Association for the Advancement of Science formulated the requirement for a coherent system of units with base units and derived units. Meanwhile, in 1875, the Treaty of the Metre passed responsibility for verification of the kilogram, in 1921, the Treaty was extended to include all physical quantities including electrical units originally defined in 1893. The units associated with these quantities were the metre, kilogram, second, ampere, kelvin, in 1971, a seventh base quantity, amount of substance represented by the mole, was added to the definition of SI. On 11 July 1792, the proposed the names metre, are, litre and grave for the units of length, area, capacity. The committee also proposed that multiples and submultiples of these units were to be denoted by decimal-based prefixes such as centi for a hundredth, on 10 December 1799, the law by which the metric system was to be definitively adopted in France was passed. Prior to this, the strength of the magnetic field had only been described in relative terms. The technique used by Gauss was to equate the torque induced on a magnet of known mass by the earth’s magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length, a French-inspired initiative for international cooperation in metrology led to the signing in 1875 of the Metre Convention. Initially the convention only covered standards for the metre and the kilogram, one of each was selected at random to become the International prototype metre and International prototype kilogram that replaced the mètre des Archives and kilogramme des Archives respectively. Each member state was entitled to one of each of the prototypes to serve as the national prototype for that country. Initially its prime purpose was a periodic recalibration of national prototype metres. The official language of the Metre Convention is French and the version of all official documents published by or on behalf of the CGPM is the French-language version
9.
Classical mechanics
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In physics, classical mechanics is one of the two major sub-fields of mechanics, along with quantum mechanics. Classical mechanics is concerned with the set of physical laws describing the motion of bodies under the influence of a system of forces. The study of the motion of bodies is an ancient one, making classical mechanics one of the oldest and largest subjects in science, engineering and technology. Classical mechanics describes the motion of objects, from projectiles to parts of machinery, as well as astronomical objects, such as spacecraft, planets, stars. Within classical mechanics are fields of study that describe the behavior of solids, liquids and gases, Classical mechanics also provides extremely accurate results as long as the domain of study is restricted to large objects and the speeds involved do not approach the speed of light. When both quantum and classical mechanics cannot apply, such as at the level with high speeds. Since these aspects of physics were developed long before the emergence of quantum physics and relativity, however, a number of modern sources do include relativistic mechanics, which in their view represents classical mechanics in its most developed and accurate form. Later, more abstract and general methods were developed, leading to reformulations of classical mechanics known as Lagrangian mechanics and these advances were largely made in the 18th and 19th centuries, and they extend substantially beyond Newtons work, particularly through their use of analytical mechanics. The following introduces the concepts of classical mechanics. For simplicity, it often models real-world objects as point particles, the motion of a point particle is characterized by a small number of parameters, its position, mass, and the forces applied to it. Each of these parameters is discussed in turn, in reality, the kind of objects that classical mechanics can describe always have a non-zero size. Objects with non-zero size have more complicated behavior than hypothetical point particles, because of the degrees of freedom. However, the results for point particles can be used to such objects by treating them as composite objects. The center of mass of a composite object behaves like a point particle, Classical mechanics uses common-sense notions of how matter and forces exist and interact. It assumes that matter and energy have definite, knowable attributes such as where an object is in space, non-relativistic mechanics also assumes that forces act instantaneously. The position of a point particle is defined with respect to a fixed reference point in space called the origin O, in space. A simple coordinate system might describe the position of a point P by means of a designated as r. In general, the point particle need not be stationary relative to O, such that r is a function of t, the time
10.
Newton's laws of motion
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Newtons laws of motion are three physical laws that, together, laid the foundation for classical mechanics. They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces. More precisely, the first law defines the force qualitatively, the second law offers a measure of the force. These three laws have been expressed in different ways, over nearly three centuries, and can be summarised as follows. The three laws of motion were first compiled by Isaac Newton in his Philosophiæ Naturalis Principia Mathematica, Newton used them to explain and investigate the motion of many physical objects and systems. For example, in the volume of the text, Newton showed that these laws of motion, combined with his law of universal gravitation. Newtons laws are applied to objects which are idealised as single point masses, in the sense that the size and this can be done when the object is small compared to the distances involved in its analysis, or the deformation and rotation of the body are of no importance. In this way, even a planet can be idealised as a particle for analysis of its orbital motion around a star, in their original form, Newtons laws of motion are not adequate to characterise the motion of rigid bodies and deformable bodies. Leonhard Euler in 1750 introduced a generalisation of Newtons laws of motion for rigid bodies called Eulers laws of motion, if a body is represented as an assemblage of discrete particles, each governed by Newtons laws of motion, then Eulers laws can be derived from Newtons laws. Eulers laws can, however, be taken as axioms describing the laws of motion for extended bodies, Newtons laws hold only with respect to a certain set of frames of reference called Newtonian or inertial reference frames. Other authors do treat the first law as a corollary of the second, the explicit concept of an inertial frame of reference was not developed until long after Newtons death. In the given mass, acceleration, momentum, and force are assumed to be externally defined quantities. This is the most common, but not the interpretation of the way one can consider the laws to be a definition of these quantities. Newtonian mechanics has been superseded by special relativity, but it is useful as an approximation when the speeds involved are much slower than the speed of light. The first law states that if the net force is zero, the first law can be stated mathematically when the mass is a non-zero constant, as, ∑ F =0 ⇔ d v d t =0. Consequently, An object that is at rest will stay at rest unless a force acts upon it, an object that is in motion will not change its velocity unless a force acts upon it. This is known as uniform motion, an object continues to do whatever it happens to be doing unless a force is exerted upon it. If it is at rest, it continues in a state of rest, if an object is moving, it continues to move without turning or changing its speed
11.
Acceleration
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Acceleration, in physics, is the rate of change of velocity of an object with respect to time. An objects acceleration is the net result of any and all forces acting on the object, the SI unit for acceleration is metre per second squared. Accelerations are vector quantities and add according to the parallelogram law, as a vector, the calculated net force is equal to the product of the objects mass and its acceleration. For example, when a car starts from a standstill and travels in a line at increasing speeds. If the car turns, there is an acceleration toward the new direction, in this example, we can call the forward acceleration of the car a linear acceleration, which passengers in the car might experience as a force pushing them back into their seats. When changing direction, we call this non-linear acceleration, which passengers might experience as a sideways force. If the speed of the car decreases, this is an acceleration in the direction from the direction of the vehicle. Passengers may experience deceleration as a force lifting them forwards, mathematically, there is no separate formula for deceleration, both are changes in velocity. Each of these accelerations might be felt by passengers until their velocity matches that of the car, an objects average acceleration over a period of time is its change in velocity divided by the duration of the period. Mathematically, a ¯ = Δ v Δ t, instantaneous acceleration, meanwhile, is the limit of the average acceleration over an infinitesimal interval of time. The SI unit of acceleration is the metre per second squared, or metre per second per second, as the velocity in metres per second changes by the acceleration value, every second. An object moving in a circular motion—such as a satellite orbiting the Earth—is accelerating due to the change of direction of motion, in this case it is said to be undergoing centripetal acceleration. Proper acceleration, the acceleration of a relative to a free-fall condition, is measured by an instrument called an accelerometer. As speeds approach the speed of light, relativistic effects become increasingly large and these components are called the tangential acceleration and the normal or radial acceleration. Geometrical analysis of space curves, which explains tangent, normal and binormal, is described by the Frenet–Serret formulas. Uniform or constant acceleration is a type of motion in which the velocity of an object changes by an amount in every equal time period. A frequently cited example of uniform acceleration is that of an object in free fall in a gravitational field. The acceleration of a body in the absence of resistances to motion is dependent only on the gravitational field strength g
12.
Symbol
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A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different concepts and experiences, all communication is achieved through the use of symbols. Symbols take the form of words, sounds, gestures, ideas or visual images and are used to other ideas. For example, a red octagon may be a symbol for STOP, on a map, a blue line might represent a river. Alphabetic letters may be symbols for sounds, personal names are symbols representing individuals. A red rose may symbolize love and compassion, the variable x, in a mathematical equation, may symbolize the position of a particle in space. In cartography, a collection of symbols forms a legend for a map The word derives from the Greek symbolon meaning token or watchword. It is an amalgam of syn- together + bole a throwing, a casting, the sense evolution in Greek is from throwing things together to contrasting to comparing to token used in comparisons to determine if something is genuine. The meaning something which stands for something else was first recorded in 1590, later, expanding on what he means by this definition Campbell says, a symbol, like everything else, shows a double aspect. We must distinguish, therefore between the sense and the meaning of the symbol. The term meaning can only to the first two but these, today, are in the charge of science – which is the province as we have said, not of symbols. The ineffable, the unknowable, can be only sensed. Heinrich Zimmer gives an overview of the nature, and perennial relevance. Concepts and words are symbols, just as visions, rituals, through all of these a transcendent reality is mirrored. They are so many metaphors reflecting and implying something which, though thus variously expressed, is ineffable, though thus rendered multiform, Symbols hold the mind to truth but are not themselves the truth, hence it is delusory to borrow them. Each civilisation, every age, must bring forth its own, in the book Signs and Symbols, it is stated that A symbol. Is a visual image or sign representing an idea -- a deeper indicator of a universal truth, Symbols are a means of complex communication that often can have multiple levels of meaning. This separates symbols from signs, as signs have only one meaning, human cultures use symbols to express specific ideologies and social structures and to represent aspects of their specific culture
13.
Letter case
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Letter case is the distinction between the letters that are in larger upper case and smaller lower case in the written representation of certain languages. The writing systems that distinguish between the upper and lower case have two sets of letters, with each letter in one set usually having an equivalent in the other set. Basically, the two variants are alternative representations of the same letter, they have the same name and pronunciation. Letter case is generally applied in a fashion, with both upper- and lower-case letters appearing in a given piece of text. The choice of case is often prescribed by the grammar of a language or by the conventions of a particular discipline, in mathematics, letter case may indicate the relationship between objects, with upper-case letters often representing superior objects. In some contexts, it is conventional to use only one case, the terms upper case and lower case can be written as two consecutive words, connected with a hyphen, or as a single word. These terms originated from the layouts of the shallow drawers called type cases used to hold the movable type for letterpress printing. Traditionally, the letters were stored in a separate case that was located above the case that held the small letters. Majuscule, for palaeographers, is technically any script in which the letters have very few or very short ascenders and descenders, or none at all. By virtue of their impact, this made the term majuscule an apt descriptor for what much later came to be more commonly referred to as uppercase letters. The word is often spelled miniscule, by association with the word miniature. This has traditionally been regarded as a mistake, but is now so common that some dictionaries tend to accept it as a nonstandard or variant spelling. Miniscule is still less likely, however, to be used in reference to lower-case letters, the glyphs of lower-case letters can resemble smaller forms of the upper-case glyphs restricted to the base band or can look hardly related. There is more variation in the height of the minuscules, as some of them have higher or lower than the typical size. In Times New Roman, for instance, b, d, f, h, k, l, t are the letters with ascenders, and g, j, p, q, y are the ones with descenders. In addition, with old-style numerals still used by traditional or classical fonts,6 and 8 make up the ascender set. Writing systems using two separate cases are bicameral scripts, languages that use the Latin, Cyrillic, Greek, Coptic, Armenian, Adlam, Varang Kshiti, Cherokee, and Osage scripts use letter cases in their written form as an aid to clarity. Other bicameral scripts, which are not used for any modern languages, are Old Hungarian, Glagolitic, the Georgian alphabet has several variants, and there were attempts to use them as different cases, but the modern written Georgian language does not distinguish case
14.
Dimensional analysis
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Converting from one dimensional unit to another is often somewhat complex. Dimensional analysis, or more specifically the method, also known as the unit-factor method, is a widely used technique for such conversions using the rules of algebra. The concept of physical dimension was introduced by Joseph Fourier in 1822, Physical quantities that are measurable have the same dimension and can be directly compared to each other, even if they are originally expressed in differing units of measure. If physical quantities have different dimensions, they cannot be compared by similar units, hence, it is meaningless to ask whether a kilogram is greater than, equal to, or less than an hour. Any physically meaningful equation will have the dimensions on their left and right sides. Checking for dimensional homogeneity is an application of dimensional analysis. Dimensional analysis is routinely used as a check of the plausibility of derived equations and computations. It is generally used to categorize types of quantities and units based on their relationship to or dependence on other units. Many parameters and measurements in the sciences and engineering are expressed as a concrete number – a numerical quantity. Often a quantity is expressed in terms of other quantities, for example, speed is a combination of length and time. Compound relations with per are expressed with division, e. g.60 mi/1 h, other relations can involve multiplication, powers, or combinations thereof. A base unit is a unit that cannot be expressed as a combination of other units, for example, units for length and time are normally chosen as base units. Units for volume, however, can be factored into the units of length. Sometimes the names of units obscure that they are derived units, for example, an ampere is a unit of electric current, which is equivalent to electric charge per unit time and is measured in coulombs per second, so 1 A =1 C/s. Similarly, one newton is 1 kg⋅m/s2, percentages are dimensionless quantities, since they are ratios of two quantities with the same dimensions. In other words, the % sign can be read as 1/100, derivatives with respect to a quantity add the dimensions of the variable one is differentiating with respect to on the denominator. Thus, position has the dimension L, derivative of position with respect to time has dimension LT−1 – length from position, time from the derivative, the second derivative has dimension LT−2. In economics, one distinguishes between stocks and flows, a stock has units of units, while a flow is a derivative of a stock, in some contexts, dimensional quantities are expressed as dimensionless quantities or percentages by omitting some dimensions
15.
Gravity of Earth
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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
16.
Tractive force
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In railway engineering, the term tractive effort is often used synonymously with tractive force to describe the pulling or pushing capability of a locomotive. The published tractive force value for any vehicle may be theoretical—that is, the term tractive effort is often qualified as starting tractive effort, continuous tractive effort and maximum tractive effort. The product of μ and m is the factor of adhesion, Starting tractive effort, Starting tractive effort is the tractive force that can be generated at a standstill. This figure is important on railways because it determines the maximum weight that a locomotive can set into motion. Maximum tractive effort, Maximum tractive effort is defined as the highest tractive force that can be generated under any condition that is not injurious to the vehicle or machine. In most cases, maximum tractive effort is developed at low speed, due to the relationship between power, velocity and force, described as, P = vF or P/v = F tractive effort inversely varies with speed at any given level of available power. Continuous tractive effort is often shown in graph form at a range of speeds as part of a tractive effort curve, the period of time for which the maximum continuous tractive effort may be safely generated is usually limited by thermal considerations. Such as temperature rise in a traction motor, specifications of locomotives often include tractive effort curves, showing the relationship between tractive effort and velocity. The shape of the graph is shown at right, the line AB shows operation at the maximum tractive effort, the line BC shows continuous tractive effort that is inversely proportional to speed. Tractive effort curves often have graphs of rolling resistance superimposed on them—the intersection of the rolling resistance graph, once in motion, the train will develop additional drag as it accelerates due to aerodynamic forces, which increase with the square of the speed. Drag may also be produced at speed due to truck hunting, if acceleration continues, the train will eventually attain a speed at which the available tractive force of the locomotive will exactly offset the total drag, causing acceleration to cease. This top speed will be increased on a due to gravity assisting the motive power. Tractive effort can be calculated from a locomotives mechanical characteristics, or by actual testing with drawbar strain sensors. Power at rail is a term for the available power for traction, that is. An estimate for the effort of a single cylinder steam locomotive can be obtained from the cylinder pressure, cylinder area, stroke of the piston. The torque developed by the motion of the piston depends on the angle that the driving rod makes with the tangent of the radius on the driving wheel. For a more useful value an average value over the rotation of the wheel is used, the driving force is the torque divided by the wheel radius. Modern locomotives with roller bearings were probably underestimated, european designers used a constant of 0.6 instead of 0.85, so the two cannot be compared without a conversion factor
17.
NER Class Y
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The North Eastern Railway Class Y 4-6-2T tank locomotives were designed whilst Wilson Worsdell was Chief Mechanical Engineer, but none were built until 1910 by which time Vincent Raven had taken over. The Class Y locomotives were intended for hauling coal trains and were developed from the NER Class X 4-8-0T heavy shunters, however, they had larger boilers and smaller cylinders for higher working speeds. Twenty were built in one batch and numbered between 1113 and 1195, originally built with saturated boilers pressed to 175 lbf/in2, seven locomotives were later fitted with boilers equipped with superheaters and pressed to 160 lbf/in2. All twenty locomotives passed to the London and North Eastern Railway at the 1923 Grouping, the LNER left the NERs locomotive numbers unchanged, but raised the boiler pressure of the saturated locomotives to 180 lbf/in2. They also fitted ten more locomotives with the 160 lbf/in2 superheated boilers that the LNER classified as diagram 55, by the time the A7s entered LNER ownership in 1923, the A7s had been relegated to shunting in the larger marshalling yards. Their power was invaluable when shunting heavy trains over the shunting hump, in the 1930s, Nos.1136 and 1175 were allocated to hauling chalk quarry trains from Hessle Quarry to Stoneferry Cement Works, in the Hull area. Heavy mineral traffic declined after the end of World War II, at Hull, the A7s replaced the old Hull and Barnsley Railway types which were being withdrawn at that time. During LNER ownership in the 1940s, two locomotives were rebuilt with diagram 63B superheated boilers pressed to 175 lbf/in2, the locomotives were assigned to Class A7/1. BR continued the scheme, dealing with another 13 locomotives, although one received a diagram 63B saturated boiler. Both were pressed to 175 lbf/in2, the A7s were withdrawn between 1951 and 1957 and none have survived into preservation. Fry, E. V. ed. Locomotives of the L. N. E. R, part 7, Tank Engines - Classes A5 to H2. Ian Allan ABC of British Railways Locomotives, part 4
18.
Thrust
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Thrust is a reaction force described quantitatively by Isaac Newtons second and third laws. When a system expels or accelerates mass in one direction, the mass will cause a force of equal magnitude. The force applied on a surface in a direction perpendicular or normal to the surface is called thrust. Force, and thus thrust, is measured in the International System of Units as the newton, in mechanical engineering, force orthogonal to the main load is referred to as thrust. A fixed-wing aircraft generates forward thrust when air is pushed in the direction opposite to flight. This can be done in several ways including by the blades of a propeller, or a rotating fan pushing air out from the back of a jet engine. The forward thrust is proportional to the mass of the airstream multiplied by the difference in velocity of the airstream, reverse thrust can be generated to aid braking after landing by reversing the pitch of variable-pitch propeller blades, or using a thrust reverser on a jet engine. Rotary wing aircraft and thrust vectoring V/STOL aircraft use engine thrust to support the weight of the aircraft, a motorboat generates thrust when the propellers are turned to accelerate water backwards. The resulting thrust pushes the boat in the direction from the combustion chamber through the rocket engine nozzle. For vertical launch of a rocket the initial thrust at liftoff must be more than the weight. Each of the three Space Shuttle Main Engines could produce a thrust of 1.8 MN, and each of the Space Shuttles two Solid Rocket Boosters 14.7 MN, together 29.4 MN. By contrast, the simplified Aid For EVA Rescue has 24 thrusters of 3.56 N each, in the air-breathing category, the AMT-USA AT-180 jet engine developed for radio-controlled aircraft produce 90 N of thrust. The GE90-115B engine fitted on the Boeing 777-300ER, recognized by the Guinness Book of World Records as the Worlds Most Powerful Commercial Jet Engine, has a thrust of 569 kN. The power needed to generate thrust and the force of the thrust can be related in a non-linear way and this helps to explain why moving through water is easier and why aircraft have much larger propellers than watercraft do. A very common question is how to contrast the thrust rating of a jet engine with the rating of a piston engine. Such comparison is difficult, as quantities are not equivalent. A piston engine does not move the aircraft by itself, so piston engines are rated by how much power they deliver to the propeller. Except for changes in temperature and air pressure, this quantity depends basically on the throttle setting, a jet engine has no propeller, so the propulsive power of a jet engine is determined from its thrust as follows
19.
Pratt & Whitney F100
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The Pratt & Whitney F100 is an afterburning turbofan engine manufactured by Pratt & Whitney which powers the F-15 Eagle and F-16 Fighting Falcon. In 1967, the United States Navy and United States Air Force issued a joint engine Request for Proposals for the F-14 Tomcat, the combined program was called Advanced Turbine Engine Gas Generator with goals to improve thrust and reduce weight to achieve a thrust-to-weight ratio of 9. The program requested proposals and would award Pratt & Whitney a contract in 1970 to produce F100-PW-100 and F401-PW-400 engines, the Navy would cut back and later cancel its order, choosing to continue to use the Pratt & Whitney TF30 engine from the F-111 in its F-14. The F100-100 first flew in an F-15 Eagle in 1972 with a thrust of 23,930 lbf, due to the advanced nature of engine and aircraft, numerous problems were encountered in its early days of service including high wear, stalling and hard afterburner starts. Early problems were solved in the F100-PW-220, and the engine is still in the USAF fleet to this day, the F-16 Fighting Falcon entered service with the F100-200, with only slight differences from the -100. Seeking a way to unit costs down, the USAF implemented the Alternative Fighter Engine program in 1984. The F-16C/D Block 30/32s were the first to be built with the engine bay. Due to the reliability, maintenance costs, and service life of the F100-PW-100/200. The resulting engine, designated F100-PW-220, almost eliminates stall-stagnations and augmenter instability as well as doubling time between depot overhauls, reliability and maintenance costs were also drastically improved, and the engine incorporates a digital electronic engine control. The F100-PW-220 was introduced in 1986 and could be installed on either an F-15 or F-16, a non-afterburning variant, the F100-PW-220U powers the Northrop Grumman X-47B UCAV. The E abbreviation from 220E is for equivalent, the abbreviation is given to engines which have been upgraded from series 100 or 200 to 220, thus becoming equivalent to 220 specifications. The first -229 was flown in 1989 and has a thrust of 17,800 lbf and 29,160 lbf with afterburner and it currently powers late model F-16s and the F-15E Strike Eagle. F100 page on Pratt & Whitneys site F100-PW-100/-200 page on GlobalSecurity. com F100 page on LeteckeMotory. cz
20.
Fastener
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A fastener is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints, that is, welding is an example of creating permanent joints. There are also special-purpose closing devices, e. g. a bread clip, furniture supplied in flat-pack form often uses cam dowels locked by cam locks, also known as conformat fasteners. Items like a rope, string, wire, cable, chain, or plastic wrap may be used to mechanically join objects, but are not generally categorized as fasteners because they have additional common uses. Likewise, hinges and springs may join together, but are ordinarily not considered fasteners because their primary purpose is to allow articulation rather than rigid affixment. Other alternative methods of joining materials include, crimping, welding, soldering, brazing, taping, gluing, cementing, the use of force may also be used, such as with magnets, vacuum, or even friction. There are three major steel fasteners used in industries, stainless steel, carbon steel, and alloy steel, the major grade used in stainless steel fasteners,200 series,300 series, and 400 series. In 2005, it is estimated that the United States fastener industry runs 350 manufacturing plants, the industry is strongly tied to the production of automobiles, aircraft, appliances, agricultural machinery, commercial construction, and infrastructure. More than 200 billion fasteners are used per year in the U. S.26 billion of these by the automotive industry, the largest distributor of fasteners in North America is the Fastenal Company. When selecting a fastener for industrial applications, it is important to consider a variety of factors, the threading, the applied load on the fastener, the stiffness of the fastener, and the number of fasteners needed should all be taken into account. Industrial Fastener Materials There are three major steel fasteners used in industries, stainless steel, carbon steel, and alloy steel, the major grade used in stainless steel fasteners,200 series,300 series, and 400 series. Titanium, aluminum, and various alloys are common materials of construction for metal fasteners. In many cases, special coatings or plating may be applied to metal fasteners to improve their performance characteristics by, for example, common coatings/platings include zinc, chrome, and hot dip galvanizing. When choosing a fastener for an application, it is important to know the specifics of that application to help select the proper material for the intended use. External thread, thread on the outside of a fastener, internal thread, thread on the inside of a fastener. Right hand thread, thread is “right hand” when, viewed axially, it winds in a clockwise and receding direction around the fastener, all threads are right hand unless otherwise designated. Left hand thread, thread is “left hand” when, viewed axially, it winds in a counterclockwise and receding direction around the fastener, left hand threads are designated LH. Pitch, the distance from one point on a thread to a corresponding point on an adjacent thread, pitch is measured parallel to its axis in the same axial plane
21.
Construction
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Construction is the process of constructing a building or infrastructure. Construction as an industry comprises six to nine percent of the domestic product of developed countries. Construction starts with planning, design, and financing, and continues until the project is built, large-scale construction requires collaboration across multiple disciplines. An architect normally manages the job, and a manager, design engineer. For the successful execution of a project, effective planning is essential, the largest construction projects are referred to as megaprojects. Construction is a term meaning the art and science to form objects, systems, or organizations. Construction is used as a verb, the act of building, and a noun, how a building was built, in general, there are three sectors of construction, buildings, infrastructure and industrial. Building construction is further divided into residential and non-residential. Infrastructure is often called heavy/highway, heavy civil or heavy engineering and it includes large public works, dams, bridges, highways, water/wastewater and utility distribution. Industrial includes refineries, process chemical, power generation, mills, there are other ways to break the industry into sectors or markets. Engineering News-Record is a magazine for the construction industry. Each year, ENR compiles and reports on data about the size of design and they publish a list of the largest companies in the United States and also a list the largest global firms. In 2014, ENR compiled the data in nine market segments and it was divided as transportation, petroleum, buildings, power, industrial, water, manufacturing, sewer/waste, telecom, hazardous waste plus a tenth category for other projects. In their reporting on the Top 400, they used data on transportation, sewer, hazardous waste, the Standard Industrial Classification and the newer North American Industry Classification System have a classification system for companies that perform or otherwise engage in construction. To recognize the differences of companies in this sector, it is divided into three subsectors, building construction, heavy and civil engineering construction, and specialty trade contractors, there are also categories for construction service firms and construction managers. Building construction is the process of adding structure to real property or construction of buildings, the majority of building construction jobs are small renovations, such as addition of a room, or renovation of a bathroom. Often, the owner of the property acts as laborer, paymaster, for this reason, those with experience in the field make detailed plans and maintain careful oversight during the project to ensure a positive outcome. Residential construction practices, technologies, and resources must conform to local building authority regulations, materials readily available in the area generally dictate the construction materials used
22.
Tension (physics)
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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 |
23.
Shear stress
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A shear stress, often denoted τ, is defined as the component of stress coplanar with a material cross section. Shear stress arises from the vector component parallel to the cross section. Normal stress, on the hand, arises from the force vector component perpendicular to the material cross section on which it acts. The formula to calculate average shear stress is force per unit area, τ = F A, where, τ = the shear stress, F = the force applied, A = the cross-sectional area of material with area parallel to the applied force vector. Pure shear stress is related to shear strain, denoted γ, by the following equation, τ = γ G where G is the shear modulus of the isotropic material. Here E is Youngs modulus and ν is Poissons ratio, beam shear is defined as the internal shear stress of a beam caused by the shear force applied to the beam. The beam shear formula is known as Zhuravskii shear stress formula after Dmitrii Ivanovich Zhuravskii who derived it in 1855. Shear stresses within a structure may be calculated by idealizing the cross-section of the structure into a set of stringers. Dividing the shear flow by the thickness of a portion of the semi-monocoque structure yields the shear stress. Any real fluids moving along solid boundary will incur a shear stress on that boundary, the no-slip condition dictates that the speed of the fluid at the boundary is zero, but at some height from the boundary the flow speed must equal that of the fluid. The region between two points is aptly named the boundary layer. For all Newtonian fluids in laminar flow the shear stress is proportional to the rate in the fluid where the viscosity is the constant of proportionality. However, for non-Newtonian fluids, this is no longer the case as for these fluids the viscosity is not constant, the shear stress is imparted onto the boundary as a result of this loss of velocity. Specifically, the shear stress is defined as, τ w ≡ τ = μ ∂ u ∂ y | y =0. For an isotropic Newtonian flow it is a scalar, while for anisotropic Newtonian flows it can be a second-order tensor too. On the other hand, given a shear stress as function of the flow velocity, the constant one finds in this case is the dynamic viscosity of the flow. On the other hand, a flow in which the viscosity were and this nonnewtonian flow is isotropic, so the viscosity is simply a scalar, μ =1 u. This relationship can be exploited to measure the shear stress
24.
Rock climbing
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Rock climbing is an activity in which participants climb up, down or across natural rock formations or artificial rock walls. The goal is to reach the summit of a formation or the endpoint of a usually pre-defined route without falling. Due to the length and extended endurance required and because accidents are likely to happen on descent than ascent. It is very rare for a climber to downclimb, especially on the larger multiple pitches, professional Rock climbing competitions have the objectives of either completing the route in the quickest possible time or attaining the farthest point on an increasingly difficult route. Scrambling, another activity involving the scaling of hills and similar formations, is similar to rock climbing, however, rock climbing is generally differentiated by its sustained use of hands to support the climbers weight as well as to provide balance. Rock climbing is a physically and mentally demanding sport, one that often tests a climbers strength, endurance, agility and it can be a dangerous activity and knowledge of proper climbing techniques and usage of specialized climbing equipment is crucial for the safe completion of routes. Because of the range and variety of rock formations around the world. Paintings dating from 200 BC show Chinese men rock climbing China woop woop, in early America, the cliff-dwelling Anasazi in the 12th century were thought to be excellent climbers. Early European climbers used rock climbing techniques as a required to reach the summit in their mountaineering exploits. In the 1880s, European rock climbing become an independent pursuit outside of mountain climbing, Rock climbing evolved gradually from an alpine necessity to a distinct athletic activity. However, climbing techniques, equipment and ethical considerations have evolved steadily, today, free climbing, climbing using holds made entirely of natural rock while using gear solely for protection and not for upward movement, is the most popular form of the sport. Free climbing has since divided into several sub-styles of climbing dependent on belay configuration. Over time, grading systems have also created in order to compare more accurately the relative difficulties of the rock climbs. In How to Rock Climb, John Long notes that for moderately skilled climbers simply getting to the top of a route is not enough, in rock climbing, style refers to the method of ascending the cliff. There are three styles of climbing, on-sight, flash, and redpoint. To on-sight a route is to ascend the wall without aid or any foreknowledge and it is considered the way to climb with the most style. Flashing is similar to on-sighting, except that the climber has previous information about the route including talking about the beta with other climbers, redpointing means to make a free ascent of the route after having first tried it. Free climbing is typically divided into styles that differ from one another depending on the choice of equipment used
25.
Rocket engine
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A rocket engine is a type of jet engine that uses only stored rocket propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines, obtaining thrust in accordance with Newtons third law, most rocket engines are internal combustion engines, although non-combusting forms also exist. Vehicles propelled by rocket engines are commonly called rockets, since they need no external material to form their jet, rocket engines can perform in a vacuum and thus can be used to propel spacecraft and ballistic missiles. Compared to other types of jet engines, rocket engines have the highest thrust, are by far the lightest, the ideal exhaust is hydrogen, the lightest of all gases, but chemical rockets produce a mix of heavier species, reducing the exhaust velocity. Rocket engines become more efficient at high velocities, since they do not require an atmosphere, they are well suited for uses at very high altitude and in space. Here, rocket is used as an abbreviation for rocket engine, chemical rockets are powered by exothermic chemical reactions of the propellant. Thermal rockets use a propellant, heated by a power source such as electric or nuclear power. Solid-fuel rockets are chemical rockets which use propellant in a solid state, liquid-propellant rockets use one or more liquid propellants fed from tanks. Hybrid rockets use a propellant in the combustion chamber, to which a second liquid or gas oxidiser or propellant is added to permit combustion. Monopropellant rockets use a single propellant decomposed by a catalyst, the most common monopropellants are hydrazine and hydrogen peroxide. Rocket engines produce thrust by the expulsion of an exhaust fluid which has accelerated to a high speed through a propelling nozzle. The fluid is usually a gas created by high pressure combustion of solid or liquid propellants, consisting of fuel and oxidiser components, within a combustion chamber. The nozzle uses the energy released by expansion of the gas to accelerate the exhaust to very high speed. An alternative to combustion is the rocket, which uses water pressurised by compressed air, carbon dioxide, nitrogen, or manual pumping. Chemical rocket propellants are most commonly used, which undergo exothermic chemical reactions which produce hot gas which is used by a rocket for propulsive purposes. Alternatively, a chemically inert reaction mass can be heated using a power source via a heat exchanger. Solid rocket propellants are prepared as a mixture of fuel and oxidising components called grain, liquid-fuelled rockets force separate fuel and oxidiser components into the combustion chamber, where they mix and burn. Hybrid rocket engines use a combination of solid and liquid or gaseous propellants, both liquid and hybrid rockets use injectors to introduce the propellant into the chamber
26.
Launch vehicle
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In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from Earths surface into outer space. A launch system includes the launch vehicle, the launch pad, Earth orbital launch vehicles typically have at least two stages, and sometimes as many as four or more. Expendable launch vehicles are designed for one-time use and they usually separate from their payload and disintegrate during atmospheric reentry. In contrast, reusable vehicles are designed to be recovered intact. The Space Shuttle was a part of a vehicle with components used for multiple orbital spaceflights. SpaceX has developed a rocket launching system to successfully bring back a part—the first stage—of their Falcon 9 and launch it again. A fully reusable VTVL design is planned for all parts of the ITS launch vehicle, Launch vehicles are often classified by the amount of mass they can carry into orbit. For example, a Proton rocket can lift 22,000 kilograms into low Earth orbit, Launch vehicles are also characterized by their number of stages. Rockets with as many as five stages have been successfully launched, additionally, launch vehicles are very often supplied with boosters supplying high early thrust, normally burning with other engines. Boosters allow the engines to be smaller, reducing the burnout mass of later stages to allow larger payloads. Other frequently reported characteristics of vehicles are the launching nation or space agency. For example, the European Space Agency is responsible for the Ariane V, many launch vehicles are considered part of a historical line of vehicles of same or similar name, e. g. the Atlas V is the latest Atlas rocket. A small-lift launch vehicle is capable of lifting up to 2,000 kg of payload into low Earth orbit, a medium-lift launch vehicle is capable of lifting 2,000 to 20,000 kg of payload into LEO. A heavy-lift launch vehicle is capable of lifting 20,000 to 50,000 kg of payload into LEO, a super-heavy lift vehicle is capable of lifting more than 50,000 kg of payload into LEO. It refers to its 1,500 kg to LEO Vega launch vehicle as light lift, sounding rockets have long been used for brief, inexpensive unmanned space and microgravity experiments. Current human-rated suborbital launch vehicles include SpaceShipOne and the upcoming SpaceShipTwo, minimizing air drag requires a reasonably high ballistic coefficient, a ratio of length to diameter greater than ten. This generally results in a vehicle that is at least 20 m long. Leaving the atmosphere as early on in the flight as possible provides a velocity loss due to air drag of around 300 m/s, Launch vehicles of sufficient size are capable of launching payloads smaller than their orbital capability, to the Moon or beyond
27.
Pound (mass)
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The pound or pound-mass is a unit of mass used in the imperial, United States customary and other systems of measurement. The international standard symbol for the pound is lb. The unit is descended from the Roman libra, the English word pound is cognate with, among others, German Pfund, Dutch pond, and Swedish pund. All ultimately derive from a borrowing into Proto-Germanic of the Latin expression lībra pondō, usage of the unqualified term pound reflects the historical conflation of mass and weight. This accounts for the modern distinguishing terms pound-mass and pound-force, the United States and countries of the Commonwealth of Nations agreed upon common definitions for the pound and the yard. Since 1 July 1959, the avoirdupois pound has been defined as exactly 0.45359237 kg. In the United Kingdom, the use of the pound was implemented in the Weights and Measures Act 1963.9144 metre exactly. An avoirdupois pound is equal to 16 avoirdupois ounces and to exactly 7,000 grains, the conversion factor between the kilogram and the international pound was therefore chosen to be divisible by 7, and an grain is thus equal to exactly 64.79891 milligrams. The US has not adopted the system despite many efforts to do so. Historically, in different parts of the world, at different points in time, and for different applications, the libra is an ancient Roman unit of mass that was equivalent to approximately 328.9 grams. It was divided into 12 unciae, or ounces, the libra is the origin of the abbreviation for pound, lb. A number of different definitions of the pound have historically used in Britain. Amongst these were the avoirdupois pound and the tower, merchants. Historically, the sterling was a tower pound of silver. In 1528, the standard was changed to the Troy pound, the avoirdupois pound, also known as the wool pound, first came into general use c. It was initially equal to 6992 troy grains, the pound avoirdupois was divided into 16 ounces. During the reign of Queen Elizabeth, the pound was redefined as 7,000 troy grains. Since then, the grain has often been a part of the avoirdupois system
28.
Foot (unit)
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The foot is a unit of length in the imperial and US customary systems of measurement. Since 1959, both units have been defined by international agreement as equivalent to 0.3048 meters exactly, in both systems, the foot comprises 12 inches and three feet compose a yard. Historically the foot was a part of local systems of units, including the Greek, Roman, Chinese, French. It varied in length from country to country, from city to city and its length was usually between 250 mm and 335 mm and was generally, but not always, subdivided into 12 inches or 16 digits. The United States is the industrialized nation that uses the international foot and the survey foot in preference to the meter in its commercial, engineering. The foot is legally recognized in the United Kingdom, road signs must use imperial units, the measurement of altitude in international aviation is one of the few areas where the foot is widely used outside the English-speaking world. The length of the international foot corresponds to a foot with shoe size of 13,14,15.5 or 46. Historically the human body has been used to provide the basis for units of length. The foot of a male is typically about 15. 3% of his height, giving a person of 160 cm a foot of 245 mm. These figures are less than the used in most cities over time. Archeologists believe that the Egyptians, Ancient Indians and Mesopotamians preferred the cubit while the Romans, under the Harappan linear measures, Indus cities during the Bronze Age used a foot of 13.2 inches and a cubit of 20.8 inches. The Egyptian equivalent of the measure of four palms or 16 digits—was known as the djeser and has been reconstructed as about 30 cm. The Greek foot had a length of 1⁄600 of a stadion, one stadion being about 181.2 m, the standard Roman foot was normally about 295.7 mm, but in the provinces, the pes Drusianus was used, with a length of about 334 mm. Originally both the Greeks and the Romans subdivided the foot into 16 digits, but in later years, after the fall of the Roman Empire, some Roman traditions were continued but others fell into disuse. In AD790 Charlemagne attempted to reform the units of measure in his domains and his units of length were based on the toise and in particular the toise de lÉcritoire, the distance between the fingertips of the outstretched arms of a man. The toise has 6 pieds each of 326.6 mm, at the same time, monastic buildings used the Carolingian foot of 340 mm. The procedure for verification of the foot as described in the 16th century by Jacob Koebel in his book Geometrei, the measures of Iron Age Britain are uncertain and proposed reconstructions such as the Megalithic Yard are controversial. Later Welsh legend credited Dyfnwal Moelmud with the establishment of their units, the Belgic or North German foot of 335 mm was introduced to England either by the Belgic Celts during their invasions prior to the Romans or by the Anglo-Saxons in the 5th & 6th century
29.
Metric system
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The metric system is an internationally agreed decimal system of measurement. Many sources also cite Liberia and Myanmar as the other countries not to have done so. Although the originators intended to devise a system that was accessible to all. Control of the units of measure was maintained by the French government until 1875, when it was passed to an intergovernmental organisation. From its beginning, the features of the metric system were the standard set of interrelated base units. These base units are used to larger and smaller units that could replace a huge number of other units of measure in existence. Although the system was first developed for use, the development of coherent units of measure made it particularly suitable for science. Although the metric system has changed and developed since its inception, designed for transnational use, it consisted of a basic set of units of measurement, now known as base units. At the outbreak of the French Revolution in 1789, most countries, the metric system was designed to be universal—in the words of the French philosopher Marquis de Condorcet it was to be for all people for all time. However, these overtures failed and the custody of the metric system remained in the hands of the French government until 1875. In languages where the distinction is made, unit names are common nouns, the concept of using consistent classical names for the prefixes was first proposed in a report by the Commission on Weights and Measures in May 1793. The prefix kilo, for example, is used to multiply the unit by 1000, thus the kilogram and kilometre are a thousand grams and metres respectively, and a milligram and millimetre are one thousandth of a gram and metre respectively. These relations can be written symbolically as,1 mg =0, however,1935 extensions to the prefix system did not follow this convention, the prefixes nano- and micro-, for example have Greek roots. During the 19th century the prefix myria-, derived from the Greek word μύριοι, was used as a multiplier for 10000, prefixes are not usually used to indicate multiples of a second greater than 1, the non-SI units of minute, hour and day are used instead. On the other hand, prefixes are used for multiples of the unit of volume. The base units used in the system must be realisable. Each of the units in SI is accompanied by a mise en pratique published by the BIPM that describes in detail at least one way in which the base unit can be measured. In practice, such realisation is done under the auspices of a mutual acceptance arrangement, in the original version of the metric system the base units could be derived from a specified length and the weight of a specified volume of pure water
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Gal (unit)
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The gal, sometimes called galileo after Galileo Galilei, is a unit of acceleration used extensively in the science of gravimetry. The gal is defined as 1 centimeter per second squared, the milligal and microgal refer respectively to one thousandth and one millionth of a gal. The gal is not part of the International System of Units, in 1978 the CIPM decided that it was permissible to use the gal with the SI until the CIPM considers that use is no longer necessary. However, use of the gal is deprecated by ISO 80000-3,2006. The gal is a unit, defined in terms of the centimeter-gram-second base unit of length, the centimeter, and the second. In SI base units,1 Gal is equal to 0.01 m/s2, the acceleration due to Earth’s gravity at its surface is 976 to 983 Gal, the variation being due mainly to differences in latitude and elevation. Mountains and masses of lesser density within the Earths crust typically cause variations in acceleration of tens to hundreds of milligals. The gravity gradient above Earths surface is about 3.1 µGal per centimeter of height, unless it is being used at the beginning of a sentence or in paragraph or section titles, the unit name gal is properly spelled with a lowercase g. As with the torr and its symbol, the unit name and its symbol are spelled identically except that the latter is capitalized
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Mass
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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
