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 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, electromagnetic, 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
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 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 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 and frequency, 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
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 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, Greek, Armenian, Varang Kshiti 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, 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
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, 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 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
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, 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
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 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 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, bridges, water/wastewater and utility distribution.
Industrial includes refineries, process chemical, power generation, 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 a list the largest global firms. In 2014, ENR compiled the data in nine market segments and it was divided as transportation, buildings, industrial, manufacturing, sewer/waste, hazardous waste plus a tenth category for other projects. In their reporting on the Top 400, they used data on transportation, 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 and civil engineering construction, and specialty trade contractors, there are 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, 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 and resources must conform to local building authority regulations, materials readily available in the area generally dictate the construction materials used
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 special-purpose closing devices, e. g. a bread clip, furniture supplied in flat-pack form often uses cam dowels locked by cam locks, known as conformat fasteners. Items like a rope, wire, 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 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, welding, brazing, gluing, the use of force may 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, 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 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 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
The metric system is an internationally agreed decimal system of measurement. Many sources 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 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
Pratt & Whitney F100
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 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 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 and maintenance costs were 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
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, 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, 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 and ethical considerations have evolved steadily, 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 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 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
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, 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, 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