1.
Pressure measurement
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Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure in a unit are called pressure gauges or vacuum gauges. A manometer is an example as it uses a column of liquid to both measure and indicate pressure. Likewise the widely used Bourdon gauge is a device which both measures and indicates, and is probably the best known type of gauge. A vacuum gauge is a pressure gauge used to measure the pressures lower than the ambient atmospheric pressure. Other methods of pressure measurement involve sensors which can transmit the pressure reading to an indicator or control system. Everyday pressure measurements, such as for vehicle tire pressure, are made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to other specific reference. Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure, to distinguish a negative pressure, the value may be appended with the word vacuum or the gauge may be labeled a vacuum gauge. These are further divided into two subcategories, high and low vacuum, the applicable pressure ranges of many of the techniques used to measure vacuums have an overlap. Hence, by combining different types of gauge, it is possible to measure system pressure continuously from 10 mbar down to 10−11 mbar. Differential pressure is the difference in pressure between two points, the zero reference in use is usually implied by context, and these words are added only when clarification is needed. Tire pressure and blood pressure are gauge pressures by convention, while atmospheric pressures, deep vacuum pressures, for most working fluids where a fluid exists in a closed system, gauge pressure measurement prevails. Pressure instruments connected to the system will indicate pressures relative to the current atmospheric pressure, the situation changes when extreme vacuum pressures are measured, absolute pressures are typically used instead. Differential pressures are used in industrial process systems. Differential pressure gauges have two ports, each connected to one of the volumes whose pressure is to be monitored. Moderate vacuum pressure readings can be ambiguous without the proper context, thus a vacuum of 26 inHg gauge is equivalent to an absolute pressure of 30 inHg −26 inHg =4 inHg. Atmospheric pressure is typically about 100 kPa at sea level, but is variable with altitude, if the absolute pressure of a fluid stays constant, the gauge pressure of the same fluid will vary as atmospheric pressure changes
2.
Pounds per square inch
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The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units. Now converting the psi to standard atmospheres,1 atm =101325 Pa =101325 Pa 6894.757293168 Pa / psi ≈14.70 psi Therefore,1 atmosphere is approximately 14.7 pounds per square inch. Pounds per square inch absolute is used to make it clear that the pressure is relative to a rather than the ambient atmospheric pressure. Since atmospheric pressure at sea level is around 14.7 psi, the converse is pounds per square inch gauge or pounds per square inch gage, indicating that the pressure is relative to atmospheric pressure. For example, a bicycle tire pumped up to 65 psi above atmospheric pressure. When gauge pressure is referenced to something other than ambient atmospheric pressure, the kilopound per square inch is a scaled unit derived from psi, equivalent to a thousand psi. Ksi are not widely used for gas pressures and they are mostly used in materials science, where the tensile strength of a material is measured as a large number of psi. The conversion in SI Units is 1 ksi =6.895 MPa, the megapound per square inch is another multiple equal to a million psi. It is used in mechanics for the modulus of the materials. The conversion in SI Units is 1 Mpsi =6.895 GPa, inch of water,0.036 psid Blood pressure – clinically normal human blood pressure,2.32 psig/1.55 psig Natural gas residential piped in for consumer appliance, 4–6 psig. Boost pressure provided by a turbocharger, 6–15 psig NFL football,12. 5–13.5 psig Atmospheric pressure at sea level,14
3.
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
4.
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
5.
Pressure
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Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the relative to the ambient pressure. Various units are used to express pressure, Pressure may also be expressed in terms of standard atmospheric pressure, the atmosphere is equal to this pressure and the torr is defined as 1⁄760 of this. Manometric units such as the centimetre of water, millimetre of mercury, Pressure is the amount of force acting per unit area. The symbol for it is p or P, the IUPAC recommendation for pressure is a lower-case p. However, upper-case P is widely used. The usage of P vs p depends upon the field in one is working, on the nearby presence of other symbols for quantities such as power and momentum. Mathematically, p = F A where, p is the pressure, F is the normal force and it relates the vector surface element with the normal force acting on it. It is incorrect to say the pressure is directed in such or such direction, the pressure, as a scalar, has no direction. The force given by the relationship to the quantity has a direction. If we change the orientation of the element, the direction of the normal force changes accordingly. Pressure is distributed to solid boundaries or across arbitrary sections of normal to these boundaries or sections at every point. It is a parameter in thermodynamics, and it is conjugate to volume. The SI unit for pressure is the pascal, equal to one newton per square metre and this name for the unit was added in 1971, before that, pressure in SI was expressed simply in newtons per square metre. Other units of pressure, such as pounds per square inch, the CGS unit of pressure is the barye, equal to 1 dyn·cm−2 or 0.1 Pa. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre, but using the names kilogram, gram, kilogram-force, or gram-force as units of force is expressly forbidden in SI. The technical atmosphere is 1 kgf/cm2, since a system under pressure has potential to perform work on its surroundings, pressure is a measure of potential energy stored per unit volume. It is therefore related to density and may be expressed in units such as joules per cubic metre. Similar pressures are given in kilopascals in most other fields, where the prefix is rarely used
6.
Stress (physics)
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For example, when a solid vertical bar is supporting a weight, each particle in the bar pushes on the particles immediately below it. When a liquid is in a container under pressure, each particle gets pushed against by all the surrounding particles. The container walls and the pressure-inducing surface push against them in reaction and these macroscopic forces are actually the net result of a very large number of intermolecular forces and collisions between the particles in those molecules. Strain inside a material may arise by various mechanisms, such as stress as applied by external forces to the material or to its surface. Any strain of a material generates an internal elastic stress, analogous to the reaction force of a spring. In liquids and gases, only deformations that change the volume generate persistent elastic stress, however, if the deformation is gradually changing with time, even in fluids there will usually be some viscous stress, opposing that change. Elastic and viscous stresses are usually combined under the mechanical stress. Significant stress may exist even when deformation is negligible or non-existent, stress may exist in the absence of external forces, such built-in stress is important, for example, in prestressed concrete and tempered glass. Stress may also be imposed on a material without the application of net forces, for example by changes in temperature or chemical composition, stress that exceeds certain strength limits of the material will result in permanent deformation or even change its crystal structure and chemical composition. In some branches of engineering, the stress is occasionally used in a looser sense as a synonym of internal force. For example, in the analysis of trusses, it may refer to the total traction or compression force acting on a beam, since ancient times humans have been consciously aware of stress inside materials. Until the 17th century the understanding of stress was largely intuitive and empirical, with those tools, Augustin-Louis Cauchy was able to give the first rigorous and general mathematical model for stress in a homogeneous medium. Cauchy observed that the force across a surface was a linear function of its normal vector, and, moreover. The understanding of stress in liquids started with Newton, who provided a formula for friction forces in parallel laminar flow. Stress is defined as the force across a small boundary per unit area of that boundary, following the basic premises of continuum mechanics, stress is a macroscopic concept. In a fluid at rest the force is perpendicular to the surface, in a solid, or in a flow of viscous liquid, the force F may not be perpendicular to S, hence the stress across a surface must be regarded a vector quantity, not a scalar. Moreover, the direction and magnitude depend on the orientation of S. Thus the stress state of the material must be described by a tensor, called the stress tensor, with respect to any chosen coordinate system, the Cauchy stress tensor can be represented as a symmetric matrix of 3×3 real numbers
7.
Blaise Pascal
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Blaise Pascal was a French mathematician, physicist, inventor, writer and Christian philosopher. He was a prodigy who was educated by his father. Pascal also wrote in defence of the scientific method, in 1642, while still a teenager, he started some pioneering work on calculating machines. After three years of effort and 50 prototypes, he built 20 finished machines over the following 10 years, following Galileo Galilei and Torricelli, in 1647, he rebutted Aristotles followers who insisted that nature abhors a vacuum. Pascals results caused many disputes before being accepted, in 1646, he and his sister Jacqueline identified with the religious movement within Catholicism known by its detractors as Jansenism. Following a religious experience in late 1654, he began writing works on philosophy. His two most famous works date from this period, the Lettres provinciales and the Pensées, the set in the conflict between Jansenists and Jesuits. In that year, he wrote an important treatise on the arithmetical triangle. Between 1658 and 1659 he wrote on the cycloid and its use in calculating the volume of solids, Pascal had poor health, especially after the age of 18, and he died just two months after his 39th birthday. Pascal was born in Clermont-Ferrand, which is in Frances Auvergne region and he lost his mother, Antoinette Begon, at the age of three. His father, Étienne Pascal, who also had an interest in science and mathematics, was a local judge, Pascal had two sisters, the younger Jacqueline and the elder Gilberte. In 1631, five years after the death of his wife, the newly arrived family soon hired Louise Delfault, a maid who eventually became an instrumental member of the family. Étienne, who never remarried, decided that he alone would educate his children, for they all showed extraordinary intellectual ability, the young Pascal showed an amazing aptitude for mathematics and science. Particularly of interest to Pascal was a work of Desargues on conic sections and it states that if a hexagon is inscribed in a circle then the three intersection points of opposite sides lie on a line. Pascals work was so precocious that Descartes was convinced that Pascals father had written it, in France at that time offices and positions could be—and were—bought and sold. In 1631 Étienne sold his position as president of the Cour des Aides for 65,665 livres. The money was invested in a government bond which provided, if not a lavish, then certainly a comfortable income which allowed the Pascal family to move to, but in 1638 Richelieu, desperate for money to carry on the Thirty Years War, defaulted on the governments bonds. Suddenly Étienne Pascals worth had dropped from nearly 66,000 livres to less than 7,300 and it was only when Jacqueline performed well in a childrens play with Richelieu in attendance that Étienne was pardoned
8.
SI base unit
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The International System of Units defines seven units of measure as a basic set from which all other SI units can be derived. The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science, thus, the kelvin, named after Lord Kelvin, has the symbol K and the ampere, named after André-Marie Ampère, has the symbol A. Many other units, such as the litre, are not part of the SI. The definitions of the units have been modified several times since the Metre Convention in 1875. Since the redefinition of the metre in 1960, the kilogram is the unit that is directly defined in terms of a physical artifact. However, the mole, the ampere, and the candela are linked through their definitions to the mass of the platinum–iridium cylinder stored in a vault near Paris. It has long been an objective in metrology to define the kilogram in terms of a fundamental constant, two possibilities have attracted particular attention, the Planck constant and the Avogadro constant. The 23rd CGPM decided to postpone any formal change until the next General Conference in 2011
9.
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
10.
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
11.
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
12.
US customary units
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United States customary units are a system of measurements commonly used in the United States. The United States customary system developed from English units which were in use in the British Empire before the US declared its independence, however, the British system of measures was overhauled in 1824 to create the imperial system, changing the definitions of some units. Therefore, while many U. S. units are similar to their Imperial counterparts. The majority of U. S. customary units were redefined in terms of the meter and these definitions were refined by the international yard and pound agreement of 1959. Americans primarily use customary units in commercial activities, as well as for personal and social use, in science, medicine, many sectors of industry and some of government, metric units are used. The International System of Units, the form of the metric system, is preferred for many uses by the U. S. National Institute of Standards. The United States system of units is similar to the British imperial system, both systems are derived from English units, a system which had evolved over the millennia before American independence, and which had its roots in Roman and Anglo-Saxon units. The customary system was championed by the U. S. -based International Institute for Preserving and Perfecting Weights, advocates of the customary system saw the French Revolutionary, or metric, system as atheistic. An auxiliary of the Institute in Ohio published a poem with wording such as down with every metric scheme and A perfect inch, one adherent of the customary system called it a just weight and a just measure, which alone are acceptable to the Lord. The U. S. government passed the Metric Conversion Act of 1975, the legislation states that the federal government has a responsibility to assist industry as it voluntarily converts to the metric system, i. e. metrification. This is most evident in U. S. labeling requirements on food products, according to the CIA Factbook, the United States is one of three nations that have not adopted the metric system as their official system of weights and measures. U. S. customary units are used on consumer products. Metric units are standard in science, medicine, as well as many sectors of industry and government, the metric system also lacks a parallel to the foot. Frequently, however, these units designate quite different sizes, for example, the mile ranged by country from one-half to five U. S. miles, foot and pound also had varying definitions. Historically, a range of non-SI units were used in the U. S. and in Britain. This article deals only with the commonly used or officially defined in the U. S. For measuring length, the U. S. customary system uses the inch, foot, yard, and mile, since July 1,1959, these have been defined on the basis of 1 yard =0.9144 meters except for some applications in surveying. The U. S. the United Kingdom and other Commonwealth countries agreed on this definition, the NAD27 was replaced in the 1980s by the North American Datum of 1983, which is defined in meters
13.
Bar (unit)
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The bar is a metric unit of pressure, but is not approved as part of the International System of Units. It is defined as equal to 100000 Pa, which is slightly less than the current average atmospheric pressure on Earth at sea level. The bar and the millibar were introduced by the Norwegian meteorologist Vilhelm Bjerknes, use of the bar is deprecated by some professional bodies in some fields. The International Astronomical Union also lists it under Non-SI units and symbols whose continued use is deprecated, as of 2004, the bar is legally recognized in countries of the European Union. Units derived from the bar include the megabar, kilobar, decibar, centibar, the notation bar, though deprecated by various bodies, represents gauge pressure, i. e. pressure in bars above ambient or atmospheric pressure. The bar is defined using the SI derived unit, pascal,1 bar ≡100000 Pa. Thus,1 bar is equal to,100 kPa 1×105 N/m21000000 Ba, notes,1 millibar =1 one-thousandth bar, or 1×10−3 bar 1 millibar =1 hectopascal. The word bar has its origin in the Greek word βάρος, the units official symbol is bar, the earlier symbol b is now deprecated and conflicts with the use of b denoting the unit barn, but it is still encountered, especially as mb to denote the millibar. Between 1793 and 1795, the bar was used for a unit of weight in an early version of the metric system. Atmospheric air pressure is given in millibars where standard sea level pressure is defined as 1013 mbar,101.3,1.013 bar. Despite the millibar not being an SI unit, meteorologists and weather reporters worldwide have long measured air pressure in millibars as the values are convenient, for example, the weather office of Environment Canada uses kilopascals and hectopascals on their weather maps. In contrast, Americans are familiar with the use of the millibar in US reports of hurricanes, in fresh water, there is an approximate numerical equivalence between the change in pressure in decibars and the change in depth from the water surface in metres. Specifically, an increase of 1 decibar occurs for every 1.019716 m increase in depth, in sea water with respect to the gravity variation, the latitude and the geopotential anomaly the pressure can be converted into meters depth according to an empirical formula. As a result, decibars are commonly used in oceanography, many engineers worldwide use the bar as a unit of pressure because, in much of their work, using pascals would involve using very large numbers. In the automotive field, turbocharger boost is often described in bars outside the USA), unicode has characters for mb and bar, but they exist only for compatibility with legacy Asian encodings and are not intended to be used in new documents. The kilobar, equivalent to 100 MPa, is used in geological systems. Bar and bara are sometimes used to indicate absolute pressures and bar and this usage is deprecated and fuller descriptions such as gauge pressure of 2 bar or 2 bar gauge are recommended.0 Unported License but not under the GFDL. Non-SI units accepted for use with the SI
14.
Internal pressure
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Internal pressure is a measure of how the internal energy of a system changes when it expands or contracts at constant temperature. It has the dimensions as pressure, the SI unit of which is the pascal. Internal pressure is given the symbol π T. The above relation can be used as a definition of a perfect gas, the relation π T =0 can be proved without the need to invoke any molecular arguments. It follows directly from the equation of state if we use the ideal gas law p V = n R T. Real gases have non-zero internal pressures because their internal energy changes as the gases expand isothermally - it can increase on expansion or decrease, the above considerations are summarized on the graph on the right. James Joule tried to measure the pressure of air in his expansion experiment by isothermally pumping high pressure air from one metal vessel into another evacuated one. The actual deviations from the perfect behaviour were not observed since they are very small, peter Atkins and Julio de Paula, Physical Chemistry 8th edition, pp. 60–61
15.
Young's modulus
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Youngs modulus, also known as the elastic modulus, is a measure of the stiffness of a solid material. It is a property of linear elastic solid materials. It defines the relationship between stress and strain in a material, Youngs modulus is named after the 19th-century British scientist Thomas Young. The term modulus is the diminutive of the Latin term modus which means measure, a solid material will deform when a load is applied to it. If it returns to its shape after the load is removed. In the range where the ratio between load and deformation remains constant, the curve is linear. Not many materials are linear and elastic beyond a small amount of deformation, although such a material cannot exist, a material with a very high Youngs modulus can be approximated as rigid. g. The technical definition is, the ratio of the stress along an axis to the strain along that axis in the range of stress in which Hookes law holds, Youngs modulus is the ratio of stress to strain, and so Youngs modulus has units of pressure. Its SI unit is therefore the pascal, the practical units used are megapascals or gigapascals. In United States customary units, it is expressed as pounds per square inch, the abbreviation ksi refers to kips per square inch. A kip is an Imperial unit of force and is equal to 1000 pounds-force, the Youngs modulus enables the calculation of the change in the dimension of a bar made of an isotropic elastic material under tensile or compressive loads. For instance, it predicts how much a material sample extends under tension or shortens under compression, the Youngs modulus directly applies to cases of uniaxial stress, that is tensile or compressive stress in one direction and no stress in the other directions. Youngs modulus is used in order to predict the deflection that will occur in a statically determinate beam when a load is applied at a point in between the beams supports. Other elastic calculations usually require the use of one additional property, such as the shear modulus. Any two of these parameters are sufficient to fully describe elasticity in an isotropic material, Youngs modulus represents the factor of proportionality in Hookes law, which relates the stress and the strain. However, Hookes law is valid under the assumption of an elastic. If the range over which Hookes law is valid is large compared to the typical stress that one expects to apply to the material. Otherwise the material is said to be non-linear, steel, carbon fiber and glass among others are usually considered linear materials, while other materials such as rubber and soils are non-linear
16.
Ultimate tensile strength
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In other words, tensile strength resists tension, whereas compressive strength resists compression. Ultimate tensile strength is measured by the stress that a material can withstand while being stretched or pulled before breaking. In the study of strength of materials, tensile strength, compressive strength, some materials break very sharply, without plastic deformation, in what is called a brittle failure. Others, which are more ductile, including most metals, experience some plastic deformation, the UTS is usually found by performing a tensile test and recording the engineering stress versus strain. The highest point of the curve is the UTS. It is a property, therefore its value does not depend on the size of the test specimen. However, it is dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, Tensile strengths are rarely used in the design of ductile members, but they are important in brittle members. They are tabulated for common materials such as alloys, composite materials, ceramics, plastics, Tensile strength can be defined for liquids as well as solids under certain conditions. Tensile strength is defined as a stress, which is measured as force per unit area, for some non-homogeneous materials it can be reported just as a force or as a force per unit width. In the International System of Units, the unit is the pascal, or, equivalently to pascals, Many materials can display linear elastic behavior, defined by a linear stress–strain relationship, as shown in the left figure up to point 3. Beyond this elastic region, for materials, such as steel. A plastically deformed specimen does not completely return to its original size, for many applications, plastic deformation is unacceptable, and is used as the design limitation. The reversal point is the stress on the engineering stress–strain curve. The UTS is not used in the design of static members because design practices dictate the use of the yield stress. It is, however, used for quality control, because of the ease of testing and it is also used to roughly determine material types for unknown samples. The UTS is a common engineering parameter to design members made of material because such materials have no yield point. Typically, the testing involves taking a sample with a fixed cross-sectional area. When testing some metals, indentation hardness correlates linearly with tensile strength and this important relation permits economically important nondestructive testing of bulk metal deliveries with lightweight, even portable equipment, such as hand-held Rockwell hardness testers
17.
Newton (unit)
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The newton is the International System of Units derived unit of force. It is named after Isaac Newton in recognition of his work on classical mechanics, see below for the conversion factors. One newton is the force needed to one kilogram of mass at the rate of one metre per second squared in direction of the applied force. In 1948, the 9th CGPM resolution 7 adopted the name newton for this force, the MKS system then became the blueprint for todays SI system of units. The newton thus became the unit of force in le Système International dUnités. This SI unit is named after Isaac Newton, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, section 5.2. Newtons second law of motion states that F = ma, where F is the applied, m is the mass of the object receiving the force. The newton is therefore, where the symbols are used for the units, N for newton, kg for kilogram, m for metre. In dimensional analysis, F = M L T2 where F is force, M is mass, L is length, at average gravity on earth, a kilogram mass exerts a force of about 9.8 newtons. An average-sized apple exerts about one newton of force, which we measure as the apples weight, for example, the tractive effort of a Class Y steam train and the thrust of an F100 fighter jet engine are both around 130 kN. One kilonewton,1 kN, is 102.0 kgf,1 kN =102 kg ×9.81 m/s2 So for example, a platform rated at 321 kilonewtons will safely support a 32,100 kilograms load. Specifications in kilonewtons are common in safety specifications for, the values of fasteners, Earth anchors. Working loads in tension and in shear, thrust of rocket engines and launch vehicles clamping forces of the various moulds in injection moulding machines used to manufacture plastic parts
18.
Polymath
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A polymath is a person whose expertise spans a significant number of different subject areas, such a person is known to draw on complex bodies of knowledge to solve specific problems. The term was first used in the 17th century, the related term, the term is often used to describe great thinkers of the Renaissance and the Enlightenment who excelled at several fields in science and the arts. In the Italian Renaissance, the idea of the polymath was expressed by Leon Battista Alberti and this term entered the lexicon during the twentieth century and has now been applied to great thinkers living before and after the Renaissance. Renaissance man was first recorded in written English in the early 20th century and it is now used to refer to great thinkers living before, during, or after the Renaissance. Leonardo da Vinci has often described as the archetype of the Renaissance man. These polymaths had an approach to education that reflected the ideals of the humanists of the time. A gentleman or courtier of that era was expected to speak several languages, play an instrument, write poetry. The idea of an education was essential to achieving polymath ability. At this time, universities did not specialize in specific areas but rather trained students in an array of science, philosophy. This universal education gave them a grounding from which they could continue into apprenticeship toward becoming a master of a specific field, aside from Renaissance man as mentioned above, similar terms in use are Homo Universalis and Uomo Universale, which translate to universal person or universal man. The related term generalist—contrasted with a used to describe a person with a general approach to knowledge. The term Universal Genius or Versatile Genius is also used, with Leonardo da Vinci as the prime example again. The term seems to be used especially when a person has made lasting contributions in at least one of the fields in which he was involved. When a person is described as having knowledge, they exhibit a vast scope of knowledge. This designation may be anachronistic, however, in the case of such as Eratosthenes whose reputation for having encyclopedic knowledge predates the existence of any encyclopedic object. One whose accomplishments are limited to athletics would not be considered a polymath in the sense of the word. An example is Howard Baker, who was called a sporting polymath by the Encyclopedia of British Football for winning high jump titles and playing cricket, football, many polymaths from across the centuries have their roots in medical applications. One of the well known polymaths, Leonardo da Vinci, was known for his immense interest in human anatomical structure
19.
Meteorology
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Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not occur until the 18th century, the 19th century saw modest progress in the field after weather observation networks were formed across broad regions. Prior attempts at prediction of weather depended on historical data, Meteorological phenomena are observable weather events that are explained by the science of meteorology. Different spatial scales are used to describe and predict weather on local, regional, Meteorology, climatology, atmospheric physics, and atmospheric chemistry are sub-disciplines of the atmospheric sciences. Meteorology and hydrology compose the interdisciplinary field of hydrometeorology, the interactions between Earths atmosphere and its oceans are part of a coupled ocean-atmosphere system. Meteorology has application in diverse fields such as the military, energy production, transport, agriculture. The word meteorology is from Greek μετέωρος metéōros lofty, high and -λογία -logia -logy, varāhamihiras classical work Brihatsamhita, written about 500 AD, provides clear evidence that a deep knowledge of atmospheric processes existed even in those times. In 350 BC, Aristotle wrote Meteorology, Aristotle is considered the founder of meteorology. One of the most impressive achievements described in the Meteorology is the description of what is now known as the hydrologic cycle and they are all called swooping bolts because they swoop down upon the Earth. Lightning is sometimes smoky, and is then called smoldering lightning, sometimes it darts quickly along, at other times, it travels in crooked lines, and is called forked lightning. When it swoops down upon some object it is called swooping lightning, the Greek scientist Theophrastus compiled a book on weather forecasting, called the Book of Signs. The work of Theophrastus remained a dominant influence in the study of weather, in 25 AD, Pomponius Mela, a geographer for the Roman Empire, formalized the climatic zone system. According to Toufic Fahd, around the 9th century, Al-Dinawari wrote the Kitab al-Nabat, ptolemy wrote on the atmospheric refraction of light in the context of astronomical observations. St. Roger Bacon was the first to calculate the size of the rainbow. He stated that a rainbow summit can not appear higher than 42 degrees above the horizon, in the late 13th century and early 14th century, Kamāl al-Dīn al-Fārisī and Theodoric of Freiberg were the first to give the correct explanations for the primary rainbow phenomenon. Theoderic went further and also explained the secondary rainbow, in 1716, Edmund Halley suggested that aurorae are caused by magnetic effluvia moving along the Earths magnetic field lines. In 1441, King Sejongs son, Prince Munjong, invented the first standardized rain gauge and these were sent throughout the Joseon Dynasty of Korea as an official tool to assess land taxes based upon a farmers potential harvest. In 1450, Leone Battista Alberti developed a swinging-plate anemometer, and was known as the first anemometer, in 1607, Galileo Galilei constructed a thermoscope
20.
Atmospheric pressure
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Atmospheric pressure, sometimes also called barometric pressure, is the pressure exerted by the weight of air in the atmosphere of Earth. In most circumstances atmospheric pressure is approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. On average, a column of air one square centimetre in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kilograms and that force is a pressure of 10.1 N/cm2 or 101 kN/m2. A column 1 square inch in cross-section would have a weight of about 14.7 lb or about 65.4 N and it is modified by the planetary rotation and local effects such as wind velocity, density variations due to temperature and variations in composition. The standard atmosphere is a unit of pressure defined as 101325 Pa, the mean sea level pressure is the average atmospheric pressure at sea level. This is the pressure normally given in weather reports on radio, television. When barometers in the home are set to match the weather reports, they measure pressure adjusted to sea level. The altimeter setting in aviation, is an atmospheric pressure adjustment, average sea-level pressure is 1013.25 mbar. In aviation weather reports, QNH is transmitted around the world in millibars or hectopascals, except in the United States, Canada, however, in Canadas public weather reports, sea level pressure is instead reported in kilopascals. The highest sea-level pressure on Earth occurs in Siberia, where the Siberian High often attains a sea-level pressure above 1050 mbar, the lowest measurable sea-level pressure is found at the centers of tropical cyclones and tornadoes, with a record low of 870 mbar. Pressure varies smoothly from the Earths surface to the top of the mesosphere, although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round. As altitude increases, atmospheric pressure decreases, one can calculate the atmospheric pressure at a given altitude. Temperature and humidity affect the atmospheric pressure, and it is necessary to know these to compute an accurate figure. The graph at right was developed for a temperature of 15 °C, at low altitudes above the sea level, the pressure decreases by about 1.2 kPa for every 100 meters. See pressure system for the effects of air pressure variations on weather, Atmospheric pressure shows a diurnal or semidiurnal cycle caused by global atmospheric tides. This effect is strongest in tropical zones, with an amplitude of a few millibars and these variations have two superimposed cycles, a circadian cycle and semi-circadian cycle. The highest adjusted-to-sea level barometric pressure recorded on Earth was 1085.7 hPa measured in Tosontsengel
21.
Barometer
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A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short term changes in the weather, numerous measurements of air pressure are used within surface weather analysis to help find surface troughs, high pressure systems and frontal boundaries. Barometers and pressure altimeters are essentially the same instrument, but used for different purposes, the main exception to this is ships at sea, which can use a barometer because their elevation does not change. Due to the presence of weather systems, aircraft altimeters may need to be adjusted as they fly between regions of varying normalized atmospheric pressure. On July 27,1630, Giovanni Battista Baliani wrote a letter to Galileo Galilei explaining an experiment he had made in which a siphon, led over a hill about twenty-one meters high, failed to work. This was a restatement of the theory of horror vacui, which dates to Aristotle, galileos ideas reached Rome in December 1638 in his Discorsi. Raffaele Magiotti and Gasparo Berti were excited by these ideas, Magiotti devised such an experiment, and sometime between 1639 and 1641, Berti carried it out. The bottom end of the tube was opened, and water that had been inside of it poured out into the basin. What was most important about this experiment was that the water had left a space above it in the tube which had no intermediate contact with air to fill it up. This seemed to suggest the possibility of a vacuum existing in the space above the water, Torricelli, a friend and student of Galileo, interpreted the results of the experiments in a novel way. He proposed that the weight of the atmosphere, not a force of the vacuum. It was traditionally thought that the air did not have weight, that is. Even Galileo had accepted the weightlessness of air as a simple truth, Torricelli questioned that assumption, and instead proposed that air had weight and that it was the latter which held up the column of water. He thought that the level the water stayed at was reflective of the force of the airs weight pushing on it. In other words, he viewed the barometer as a balance, an instrument for measurement and he needed to use a liquid that was heavier than water, and from his previous association and suggestions by Galileo, he deduced by using mercury, a shorter tube could be used. With mercury, which is about 14 times heavier than water, Pascal further devised an experiment to test the Aristotelian proposition that it was vapors from the liquid that filled the space in a barometer. His experiment compared water with wine, and since the latter was considered more spiritous, Pascal performed the experiment publicly, inviting the Aristotelians to predict the outcome beforehand. The Aristotelians predicted the wine would stand lower, however, Pascal went even further to test the mechanical theory
22.
Joule
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The joule, symbol J, is a derived unit of energy in the International System of Units. It is equal to the transferred to an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre. It is also the energy dissipated as heat when a current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule, one joule can also be defined as, The work required to move an electric charge of one coulomb through an electrical potential difference of one volt, or one coulomb volt. This relationship can be used to define the volt, the work required to produce one watt of power for one second, or one watt second. This relationship can be used to define the watt and this SI unit is named after James Prescott Joule. As with every International System of Units unit named for a person, note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, section 5.2. The CGPM has given the unit of energy the name Joule, the use of newton metres for torque and joules for energy is helpful to avoid misunderstandings and miscommunications. The distinction may be also in the fact that energy is a scalar – the dot product of a vector force. By contrast, torque is a vector – the cross product of a distance vector, torque and energy are related to one another by the equation E = τ θ, where E is energy, τ is torque, and θ is the angle swept. Since radians are dimensionless, it follows that torque and energy have the same dimensions, one joule in everyday life represents approximately, The energy required to lift a medium-size tomato 1 m vertically from the surface of the Earth. The energy released when that same tomato falls back down to the ground, the energy required to accelerate a 1 kg mass at 1 m·s−2 through a 1 m distance in space. The heat required to raise the temperature of 1 g of water by 0.24 °C, the typical energy released as heat by a person at rest every 1/60 s. The kinetic energy of a 50 kg human moving very slowly, the kinetic energy of a 56 g tennis ball moving at 6 m/s. The kinetic energy of an object with mass 1 kg moving at √2 ≈1.4 m/s, the amount of electricity required to light a 1 W LED for 1 s. Since the joule is also a watt-second and the unit for electricity sales to homes is the kW·h. For additional examples, see, Orders of magnitude The zeptojoule is equal to one sextillionth of one joule,160 zeptojoules is equivalent to one electronvolt. The nanojoule is equal to one billionth of one joule, one nanojoule is about 1/160 of the kinetic energy of a flying mosquito
23.
International Organization for Standardization
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The International Organization for Standardization is an international standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization promotes worldwide proprietary and it is headquartered in Geneva, Switzerland, and as of March 2017 works in 162 countries. It was one of the first organizations granted general consultative status with the United Nations Economic, ISO, the International Organization for Standardization, is an independent, non-governmental organization, the members of which are the standards organizations of the 162 member countries. It is the worlds largest developer of international standards and facilitates world trade by providing common standards between nations. Nearly twenty thousand standards have been set covering everything from manufactured products and technology to food safety, use of the standards aids in the creation of products and services that are safe, reliable and of good quality. The standards help businesses increase productivity while minimizing errors and waste, by enabling products from different markets to be directly compared, they facilitate companies in entering new markets and assist in the development of global trade on a fair basis. The standards also serve to safeguard consumers and the end-users of products and services, the three official languages of the ISO are English, French, and Russian. The name of the organization in French is Organisation internationale de normalisation, according to the ISO, as its name in different languages would have different abbreviations, the organization adopted ISO as its abbreviated name in reference to the Greek word isos. However, during the meetings of the new organization, this Greek word was not invoked. Both the name ISO and the logo are registered trademarks, the organization today known as ISO began in 1926 as the International Federation of the National Standardizing Associations. ISO is an organization whose members are recognized authorities on standards. Members meet annually at a General Assembly to discuss ISOs strategic objectives, the organization is coordinated by a Central Secretariat based in Geneva. A Council with a membership of 20 member bodies provides guidance and governance. The Technical Management Board is responsible for over 250 technical committees, ISO has formed joint committees with the International Electrotechnical Commission to develop standards and terminology in the areas of electrical and electronic related technologies. Information technology ISO/IEC Joint Technical Committee 1 was created in 1987 to evelop, maintain, ISO has three membership categories, Member bodies are national bodies considered the most representative standards body in each country. These are the members of ISO that have voting rights. Correspondent members are countries that do not have their own standards organization and these members are informed about ISOs work, but do not participate in standards promulgation. Subscriber members are countries with small economies and they pay reduced membership fees, but can follow the development of standards
24.
International Union of Pure and Applied Chemistry
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The International Union of Pure and Applied Chemistry /ˈaɪjuːpæk/ or /ˈjuːpæk/ is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science, IUPAC is registered in Zürich, Switzerland, and the administrative office, known as the IUPAC Secretariat, is in Research Triangle Park, North Carolina, United States. This administrative office is headed by IUPACs executive director, currently Lynn Soby, IUPAC was established in 1919 as the successor of the International Congress of Applied Chemistry for the advancement of chemistry. Its members, the National Adhering Organizations, can be national chemistry societies, national academies of sciences, there are fifty-four National Adhering Organizations and three Associate National Adhering Organizations. IUPACs Inter-divisional Committee on Nomenclature and Symbols is the world authority in developing standards for the naming of the chemical elements. Since its creation, IUPAC has been run by different committees with different responsibilities. These committees run different projects which include standardizing nomenclature, finding ways to bring chemistry to the world, IUPAC is best known for its works standardizing nomenclature in chemistry and other fields of science, but IUPAC has publications in many fields including chemistry, biology and physics. IUPAC is also known for standardizing the atomic weights of the elements through one of its oldest standing committees, the need for an international standard for chemistry was first addressed in 1860 by a committee headed by German scientist Friedrich August Kekulé von Stradonitz. This committee was the first international conference to create an international naming system for organic compounds, the ideas that were formulated in that conference evolved into the official IUPAC nomenclature of organic chemistry. IUPAC stands as a legacy of this meeting, making it one of the most important historical international collaborations of chemistry societies, since this time, IUPAC has been the official organization held with the responsibility of updating and maintaining official organic nomenclature. IUPAC as such was established in 1919, one notable country excluded from this early IUPAC is Germany. Germanys exclusion was a result of prejudice towards Germans by the Allied powers after World War I, Germany was finally admitted into IUPAC during 1929. However, Nazi Germany was removed from IUPAC during World War II, during World War II, IUPAC was affiliated with the Allied powers, but had little involvement during the war effort itself. After the war, East and West Germany were eventually readmitted to IUPAC, since World War II, IUPAC has been focused on standardizing nomenclature and methods in science without interruption. In 2016, IUPAC denounced the use of chlorine as a chemical weapon, the letter stated, Our organizations deplore the use of chlorine in this manner. According to the CWC, the use, stockpiling, distribution, IUPAC is governed by several committees that all have different responsibilities. Each committee is made up of members of different National Adhering Organizations from different countries, the steering committee hierarchy for IUPAC is as follows, All committees have an allotted budget to which they must adhere. Any committee may start a project, if a projects spending becomes too much for a committee to continue funding, it must take the issue to the Project Committee
25.
Unicode
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Unicode is a computing industry standard for the consistent encoding, representation, and handling of text expressed in most of the worlds writing systems. As of June 2016, the most recent version is Unicode 9.0, the standard is maintained by the Unicode Consortium. Unicodes success at unifying character sets has led to its widespread, the standard has been implemented in many recent technologies, including modern operating systems, XML, Java, and the. NET Framework. Unicode can be implemented by different character encodings, the most commonly used encodings are UTF-8, UTF-16 and the now-obsolete UCS-2. UTF-8 uses one byte for any ASCII character, all of which have the same values in both UTF-8 and ASCII encoding, and up to four bytes for other characters. UCS-2 uses a 16-bit code unit for each character but cannot encode every character in the current Unicode standard, UTF-16 extends UCS-2, using one 16-bit unit for the characters that were representable in UCS-2 and two 16-bit units to handle each of the additional characters. Many traditional character encodings share a common problem in that they allow bilingual computer processing, Unicode, in intent, encodes the underlying characters—graphemes and grapheme-like units—rather than the variant glyphs for such characters. In the case of Chinese characters, this leads to controversies over distinguishing the underlying character from its variant glyphs. In text processing, Unicode takes the role of providing a unique code point—a number, in other words, Unicode represents a character in an abstract way and leaves the visual rendering to other software, such as a web browser or word processor. This simple aim becomes complicated, however, because of concessions made by Unicodes designers in the hope of encouraging a more rapid adoption of Unicode, the first 256 code points were made identical to the content of ISO-8859-1 so as to make it trivial to convert existing western text. For other examples, see duplicate characters in Unicode and he explained that he name Unicode is intended to suggest a unique, unified, universal encoding. In this document, entitled Unicode 88, Becker outlined a 16-bit character model, Unicode could be roughly described as wide-body ASCII that has been stretched to 16 bits to encompass the characters of all the worlds living languages. In a properly engineered design,16 bits per character are more than sufficient for this purpose, Unicode aims in the first instance at the characters published in modern text, whose number is undoubtedly far below 214 =16,384. By the end of 1990, most of the work on mapping existing character encoding standards had been completed, the Unicode Consortium was incorporated in California on January 3,1991, and in October 1991, the first volume of the Unicode standard was published. The second volume, covering Han ideographs, was published in June 1992, in 1996, a surrogate character mechanism was implemented in Unicode 2.0, so that Unicode was no longer restricted to 16 bits. The Microsoft TrueType specification version 1.0 from 1992 used the name Apple Unicode instead of Unicode for the Platform ID in the naming table, Unicode defines a codespace of 1,114,112 code points in the range 0hex to 10FFFFhex. Normally a Unicode code point is referred to by writing U+ followed by its hexadecimal number, for code points in the Basic Multilingual Plane, four digits are used, for code points outside the BMP, five or six digits are used, as required. Code points in Planes 1 through 16 are accessed as surrogate pairs in UTF-16, within each plane, characters are allocated within named blocks of related characters
26.
Imperial units
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The system of imperial units or the imperial system is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced. The Imperial units replaced the Winchester Standards, which were in effect from 1588 to 1825, the system came into official use across the British Empire. The imperial system developed from what were first known as English units, the Weights and Measures Act of 1824 was initially scheduled to go into effect on 1 May 1825. However, the Weights and Measures Act of 1825 pushed back the date to 1 January 1826, the 1824 Act allowed the continued use of pre-imperial units provided that they were customary, widely known, and clearly marked with imperial equivalents. Apothecaries units are mentioned neither in the act of 1824 nor 1825, at the time, apothecaries weights and measures were regulated in England, Wales, and Berwick-upon-Tweed by the London College of Physicians, and in Ireland by the Dublin College of Physicians. In Scotland, apothecaries units were unofficially regulated by the Edinburgh College of Physicians, the three colleges published, at infrequent intervals, pharmacopoeiae, the London and Dublin editions having the force of law. The Medical Act of 1858 transferred to The Crown the right to publish the official pharmacopoeia and to regulate apothecaries weights, Metric equivalents in this article usually assume the latest official definition. Before this date, the most precise measurement of the imperial Standard Yard was 0.914398416 metres, in 1824, the various different gallons in use in the British Empire were replaced by the imperial gallon, a unit close in volume to the ale gallon. It was originally defined as the volume of 10 pounds of distilled water weighed in air with brass weights with the standing at 30 inches of mercury at a temperature of 62 °F. The Weights and Measures Act of 1985 switched to a gallon of exactly 4.54609 l and these measurements were in use from 1826, when the new imperial gallon was defined, but were officially abolished in the United Kingdom on 1 January 1971. In the USA, though no longer recommended, the system is still used occasionally in medicine. The troy pound was made the unit of mass by the 1824 Act, however, its use was abolished in the UK on 1 January 1879, with only the troy ounce. The Weights and Measures Act 1855 made the pound the primary unit of mass. In all the systems, the unit is the pound. For the yard, the length of a pendulum beating seconds at the latitude of Greenwich at Mean Sea Level in vacuo was defined as 39.01393 inches, the imperial system is one of many systems of English units. Although most of the units are defined in more than one system, some units were used to a much greater extent, or for different purposes. The distinctions between these systems are not drawn precisely. One such distinction is that between these systems and older British/English units/systems or newer additions, the US customary system is historically derived from the English units that were in use at the time of settlement
27.
United States customary units
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United States customary units are a system of measurements commonly used in the United States. The United States customary system developed from English units which were in use in the British Empire before the US declared its independence, however, the British system of measures was overhauled in 1824 to create the imperial system, changing the definitions of some units. Therefore, while many U. S. units are similar to their Imperial counterparts. The majority of U. S. customary units were redefined in terms of the meter and these definitions were refined by the international yard and pound agreement of 1959. Americans primarily use customary units in commercial activities, as well as for personal and social use, in science, medicine, many sectors of industry and some of government, metric units are used. The International System of Units, the form of the metric system, is preferred for many uses by the U. S. National Institute of Standards. The United States system of units is similar to the British imperial system, both systems are derived from English units, a system which had evolved over the millennia before American independence, and which had its roots in Roman and Anglo-Saxon units. The customary system was championed by the U. S. -based International Institute for Preserving and Perfecting Weights, advocates of the customary system saw the French Revolutionary, or metric, system as atheistic. An auxiliary of the Institute in Ohio published a poem with wording such as down with every metric scheme and A perfect inch, one adherent of the customary system called it a just weight and a just measure, which alone are acceptable to the Lord. The U. S. government passed the Metric Conversion Act of 1975, the legislation states that the federal government has a responsibility to assist industry as it voluntarily converts to the metric system, i. e. metrification. This is most evident in U. S. labeling requirements on food products, according to the CIA Factbook, the United States is one of three nations that have not adopted the metric system as their official system of weights and measures. U. S. customary units are used on consumer products. Metric units are standard in science, medicine, as well as many sectors of industry and government, the metric system also lacks a parallel to the foot. Frequently, however, these units designate quite different sizes, for example, the mile ranged by country from one-half to five U. S. miles, foot and pound also had varying definitions. Historically, a range of non-SI units were used in the U. S. and in Britain. This article deals only with the commonly used or officially defined in the U. S. For measuring length, the U. S. customary system uses the inch, foot, yard, and mile, since July 1,1959, these have been defined on the basis of 1 yard =0.9144 meters except for some applications in surveying. The U. S. the United Kingdom and other Commonwealth countries agreed on this definition, the NAD27 was replaced in the 1980s by the North American Datum of 1983, which is defined in meters
28.
Geophysics
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Although geophysics was only recognized as a separate discipline in the 19th century, its origins date back to ancient times. The first magnetic compasses were made from lodestones, while more modern magnetic compasses played an important role in the history of navigation, the first seismic instrument was built in 132 BC. Geophysics is applied to societal needs, such as resources, mitigation of natural hazards. Geophysics is a highly interdisciplinary subject, and geophysicists contribute to area of the Earth sciences. To provide an idea of what constitutes geophysics, this section describes phenomena that are studied in physics and how they relate to the Earth. The gravitational pull of the Moon and Sun give rise to two high tides and two low tides every lunar day, or every 24 hours and 50 minutes, therefore, there is a gap of 12 hours and 25 minutes between every high tide and between every low tide. Gravitational forces make rocks press down on rocks, increasing their density as the depth increases. Measurements of gravitational acceleration and gravitational potential at the Earths surface, the surface gravitational field provides information on the dynamics of tectonic plates. The geopotential surface called the geoid is one definition of the shape of the Earth, the geoid would be the global mean sea level if the oceans were in equilibrium and could be extended through the continents. The Earth is cooling, and the heat flow generates the Earths magnetic field through the geodynamo. The main sources of heat are the heat and radioactivity. Some heat is carried up from the bottom of the mantle by mantle plumes, the heat flow at the Earths surface is about 4.2 ×1013 W, and it is a potential source of geothermal energy. Seismic waves are vibrations that travel through the Earths interior or along its surface, the entire Earth can also oscillate in forms that are called normal modes or free oscillations of the Earth. Ground motions from waves or normal modes are measured using seismographs, if the waves come from a localized source such as an earthquake or explosion, measurements at more than one location can be used to locate the source. The locations of earthquakes provide information on plate tectonics and mantle convection, measurements of seismic waves are a source of information on the region that the waves travel through. If the density or composition of the rock changes suddenly, some waves are reflected, reflections can provide information on near-surface structure. Changes in the direction, called refraction, can be used to infer the deep structure of the Earth. Earthquakes pose a risk to humans, understanding their mechanisms, which depend on the type of earthquake, can lead to better estimates of earthquake risk and improvements in earthquake engineering
29.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
30.
Shear modulus
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Its dimensional form is M1L−1T−2, replacing force by mass times acceleration. The shear modulus is always positive, the shear modulus is one of several quantities for measuring the stiffness of materials. These moduli are not independent, and for materials they are connected via the equations 2 G = E =3 K. The shear modulus is concerned with the deformation of a solid when it experiences a force parallel to one of its surfaces while its opposite face experiences an opposing force, in the case of an object thats shaped like a rectangular prism, it will deform into a parallelepiped. Anisotropic materials such as wood, paper and also essentially all single crystals exhibit differing material response to stress or strain when tested in different directions, in this case one may need to use the full tensor-expression of the elastic constants, rather than a single scalar value. One possible definition of a fluid would be a material with zero shear modulus, in homogeneous and isotropic solids, there are two kinds of waves, pressure waves and shear waves. The velocity of a wave, is controlled by the shear modulus. The shear modulus of metals is usually observed to decrease with increasing temperature, at high pressures, the shear modulus also appears to increase with the applied pressure. Correlations between the temperature, vacancy formation energy, and the shear modulus have been observed in many metals. Several models exist that attempt to predict the shear modulus of metals, the Steinberg-Cochran-Guinan shear modulus model developed by and used in conjunction with the Steinberg-Cochran-Guinan-Lund flow stress model. The Nadal and LePoac shear modulus model that uses Lindemann theory to determine the temperature dependence and the SCG model for pressure dependence of the shear modulus. The MTS shear modulus model has the form, μ = μ0 − D exp −1 where μ0 is the shear modulus at T =0 K, the Nadal-Le Poac shear modulus model is a modified version of the SCG model. The empirical temperature dependence of the modulus in the SCG model is replaced with an equation based on Lindemann melting theory. Dynamic modulus Impulse excitation technique Shear strength Seismic moment
31.
Materials science
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The interdisciplinary field of materials science, also commonly termed materials science and engineering, involves the discovery and design of new materials, with an emphasis on solids. Materials science still incorporates elements of physics, chemistry, and engineering, as such, the field was long considered by academic institutions as a sub-field of these related fields. Materials science is a syncretic discipline hybridizing metallurgy, ceramics, solid-state physics and it is the first example of a new academic discipline emerging by fusion rather than fission. Many of the most pressing scientific problems humans currently face are due to the limits of the materials that are available, thus, breakthroughs in materials science are likely to affect the future of technology significantly. Materials scientists emphasize understanding how the history of a material influences its structure, the understanding of processing-structure-properties relationships is called the § materials paradigm. This paradigm is used to advance understanding in a variety of areas, including nanotechnology, biomaterials. Such investigations are key to understanding, for example, the causes of various accidents and incidents. The material of choice of a given era is often a defining point, phrases such as Stone Age, Bronze Age, Iron Age, and Steel Age are great examples. Originally deriving from the manufacture of ceramics and its putative derivative metallurgy, materials science is one of the oldest forms of engineering, modern materials science evolved directly from metallurgy, which itself evolved from mining and ceramics and the use of fire. Materials science has driven, and been driven by, the development of technologies such as rubbers, plastics, semiconductors. Before the 1960s, many materials science departments were named metallurgy departments, reflecting the 19th, a material is defined as a substance that is intended to be used for certain applications. There are a myriad of materials around us—they can be found in anything from buildings to spacecraft, Materials can generally be divided into two classes, crystalline and non-crystalline. The traditional examples of materials are metals, semiconductors, ceramics, New and advanced materials that are being developed include nanomaterials and biomaterials, etc. The basis of science involves studying the structure of materials. Once a materials scientist knows about this structure-property correlation, they can go on to study the relative performance of a material in a given application. The major determinants of the structure of a material and thus of its properties are its constituent chemical elements and these characteristics, taken together and related through the laws of thermodynamics and kinetics, govern a materials microstructure, and thus its properties. As mentioned above, structure is one of the most important components of the field of materials science, Materials science examines the structure of materials from the atomic scale, all the way up to the macro scale. Characterization is the way materials scientists examine the structure of a material, structure is studied at various levels, as detailed below
32.
Engineering
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The term Engineering is derived from the Latin ingenium, meaning cleverness and ingeniare, meaning to contrive, devise. Engineering has existed since ancient times as humans devised fundamental inventions such as the wedge, lever, wheel, each of these inventions is essentially consistent with the modern definition of engineering. The term engineering is derived from the engineer, which itself dates back to 1390 when an engineer originally referred to a constructor of military engines. In this context, now obsolete, a referred to a military machine. Notable examples of the obsolete usage which have survived to the present day are military engineering corps, the word engine itself is of even older origin, ultimately deriving from the Latin ingenium, meaning innate quality, especially mental power, hence a clever invention. The earliest civil engineer known by name is Imhotep, as one of the officials of the Pharaoh, Djosèr, he probably designed and supervised the construction of the Pyramid of Djoser at Saqqara in Egypt around 2630–2611 BC. Ancient Greece developed machines in both civilian and military domains, the Antikythera mechanism, the first known mechanical computer, and the mechanical inventions of Archimedes are examples of early mechanical engineering. In the Middle Ages, the trebuchet was developed, the first steam engine was built in 1698 by Thomas Savery. The development of this gave rise to the Industrial Revolution in the coming decades. With the rise of engineering as a profession in the 18th century, similarly, in addition to military and civil engineering, the fields then known as the mechanic arts became incorporated into engineering. The inventions of Thomas Newcomen and the Scottish engineer James Watt gave rise to mechanical engineering. The development of specialized machines and machine tools during the revolution led to the rapid growth of mechanical engineering both in its birthplace Britain and abroad. John Smeaton was the first self-proclaimed civil engineer and is regarded as the father of civil engineering. He was an English civil engineer responsible for the design of bridges, canals, harbours and he was also a capable mechanical engineer and an eminent physicist. Smeaton designed the third Eddystone Lighthouse where he pioneered the use of hydraulic lime and his lighthouse remained in use until 1877 and was dismantled and partially rebuilt at Plymouth Hoe where it is known as Smeatons Tower. The United States census of 1850 listed the occupation of engineer for the first time with a count of 2,000, there were fewer than 50 engineering graduates in the U. S. before 1865. In 1870 there were a dozen U. S. mechanical engineering graduates, in 1890 there were 6,000 engineers in civil, mining, mechanical and electrical. There was no chair of applied mechanism and applied mechanics established at Cambridge until 1875, the theoretical work of James Maxwell and Heinrich Hertz in the late 19th century gave rise to the field of electronics
33.
Compressive strength
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In other words, compressive strength resists compression, whereas tensile strength resists tension. In the study of strength of materials, tensile strength, compressive strength, some materials fracture at their compressive strength limit, others deform irreversibly, so a given amount of deformation may be considered as the limit for compressive load. Compressive strength is a key value for design of structures, Compressive strength is often measured on a universal testing machine, these range from very small table-top systems to ones with over 53 MN capacity. Measurements of compressive strength are affected by the specific test method, Compressive strengths are usually reported in relationship to a specific technical standard. When a specimen of material is loaded in such a way that it extends it is said to be in tension, on the other hand, if the material compresses and shortens it is said to be in compression. On an atomic level, the molecules or atoms are forced apart when in tension whereas in compression they are forced together. Since atoms in solids always try to find an equilibrium position, the phenomena prevailing on an atomic level are therefore similar. Tension tends to pull small sideways deflections back into alignment, while compression tends to amplify such deflection into buckling, Compressive strength is measured on materials, components, and structures. By definition, the compressive strength of a material is that value of uniaxial compressive stress reached when the material fails completely. The compressive strength is usually obtained experimentally by means of a compressive test, the apparatus used for this experiment is the same as that used in a tensile test. However, rather than applying a uniaxial tensile load, a uniaxial compressive load is applied, as can be imagined, the specimen is shortened as well as spread laterally. In a compression test, there is a region where the material follows Hookes Law. Hence for this region σ = E ϵ where this time E refers to the Youngs Modulus for compression, in this region, the material deforms elastically and returns to its original length when the stress is removed. This linear region terminates at what is known as the yield point, above this point the material behaves plastically and will not return to its original length once the load is removed. There is a difference between the stress and the true stress. By its basic definition the uniaxial stress is given by, σ = F A where, F = Load applied, A = Area As stated, in reality therefore the area is some function of the applied load i. e. Indeed, stress is defined as the force divided by the area at the start of the experiment, in engineering design practice, professionals mostly rely on the engineering stress. In reality, the stress is different from the engineering stress
34.
Nylon
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Nylon is a generic designation for a family of synthetic polymers, more specifically aliphatic or semi-aromatic polyamides. They can be melt-processed into fibers, films or shapes, the first example of nylon was produced on February 28,1935, by Wallace Carothers at DuPonts research facility at the DuPont Experimental Station. Nylon polymers have significant commercial applications in fibers, in shapes. Nylon is made of repeating units linked by bonds and is a type of polyamide and is frequently referred to as such. Nylon was the first commercially successful synthetic thermoplastic polymer, commercially, nylon polymer is made by reacting monomers which are either lactams, acid/amines or stoichiometric mixtures of diamines and diacids. Mixtures of these can be polymerized together to make copolymers, Nylon polymers can be mixed with a wide variety of additives to achieve many different property variations. Nylon was invented accidentally by Julian W. Hill, a chemist for DuPont under Wallace Carotherss supervision and it was only given this name at the 1939 New York Worlds Fair. The patents were owned by DuPont, Nylon was intended to be a synthetic replacement for silk and substituted for it in many different products after silk became scarce during World War II. It replaced silk in military applications such as parachutes and flak vests, after initial commercialization of nylon as a fiber, applications in the form of shapes and films were also developed. The main market for nylon shapes now is in auto components, in 1940, John W. Eckelberry of DuPont stated that the letters nyl were arbitrary and the on was copied from the suffixes of other fibers such as cotton and rayon. A later publication by DuPont explained that the name was intended to be No-Run. Since the products were not really run-proof, the vowels were swapped to produce nuron, for clarity in pronunciation, the i was changed to y. Most nylons are made from the reaction of an acid with a diamine or a lactam or amino acid with itself. In the first case, the structure is so-called ABAB similar to polyesters and polyurethanes, in the second case, the repeating unit corresponds to the single monomer. It is difficult to get the proportions exactly correct, and deviations can lead to termination at molecular weights less than a desirable 10,000 daltons. To overcome this problem, a crystalline, solid nylon salt can be formed at room temperature, using an exact 1,1 ratio of the acid, the salt is crystallized to purify it and obtain the desired precise stoichiometry. Heated to 285 °C, the salt reacts to form nylon polymer with the production of water, Wallace Carothers at DuPont patented nylon 66, but overlooked the possibility to use lactams. That synthetic route was developed by Paul Schlack at IG Farben, leading to nylon 6, the peptide bond within the caprolactam is broken with the exposed active groups on each side being incorporated into two new bonds as the monomer becomes part of the polymer backbone
35.
Hemp
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Hemp or industrial hemp, typically found in the northern hemisphere, is a variety of the Cannabis sativa plant species that is grown specifically for the industrial uses of its derived products. It is one of the fastest growing plants and was one of the first plants to be spun into usable fiber 10,000 years ago. It can be refined into a variety of items including paper, textiles, clothing, biodegradable plastics, paint, insulation, biofuel, food. Hemp has lower concentrations of THC and higher concentrations of cannabidiol, the legality of industrial hemp varies widely between countries. Some governments regulate the concentration of THC and permit only hemp that is bred with an especially low THC content, then it appears to have been borrowed into Latin, and separately into Slavic and from there into Baltic, Finnish, and Germanic languages. Following Grimms law, the k would have changed to h with the first Germanic sound shift, after which it may have been adapted into the Old English form, hænep. Another possible source of origin is Assyrian qunnabu, which was the name for a source of oil, fiber, cognates of hemp in other Germanic languages, include Dutch hennep, Danish and Norwegian, hamp, German, hanf, and Swedish, hampa. Hemp is used to make a variety of commercial and industrial products including rope, clothes, food, paper, textiles, plastics, insulation, the inner two fibers of the plant are more woody and typically have industrial applications, such as mulch, animal bedding and litter. When oxidized, hemp oil from the seeds becomes solid and can be used in the manufacture of oil-based paints, in creams as an agent, for cooking. Hemp seeds have been used in bird feed mix as well, a survey in 2003 showed that more than 95% of hemp seed sold in the European Union was used in animal and bird feed. Hemp seeds can be raw, ground into a meal, sprouted. The leaves of the plant can be consumed raw in salads. Hemp can also be made into a liquid and used for baking or for such as hemp milk, hemp juice. Hempseed oil is cold-pressed from the seed and is high in unsaturated fatty acids. In 2011, the U. S. imported $11.5 million worth of products, mostly driven by growth in demand for hemp seed. In the U. S. imported hemp can be used legally in food products,100 grams of hulled hemp seeds supply 586 calories. They are 5% water, 5% carbohydrates, 49% total fat, Hemp seeds are notable in providing 64% of the Daily Value of protein per 100 gram serving. Hempseed amino acid profile is comparable to other sources of such as meat, milk, eggs
36.
Aluminium
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Aluminium or aluminum is a chemical element in the boron group with symbol Al and atomic number 13. It is a silvery-white, soft, nonmagnetic, ductile metal, Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is combined in over 270 different minerals. The chief ore of aluminium is bauxite, Aluminium is remarkable for the metals low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the industry and important in transportation and structures, such as building facades. The oxides and sulfates are the most useful compounds of aluminium, despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals. Because of these salts abundance, the potential for a role for them is of continuing interest. Aluminium is a soft, durable, lightweight, ductile. It is nonmagnetic and does not easily ignite, a fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation. The yield strength of aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has about one-third the density and stiffness of steel and it is easily machined, cast, drawn and extruded. Aluminium atoms are arranged in a cubic structure. Aluminium has an energy of approximately 200 mJ/m2. Aluminium is a thermal and electrical conductor, having 59% the conductivity of copper. Aluminium is capable of superconductivity, with a critical temperature of 1.2 kelvin. Aluminium is the most common material for the fabrication of superconducting qubits, the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts, particularly in the presence of dissimilar metals. In highly acidic solutions, aluminium reacts with water to form hydrogen, primarily because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium
37.
Tooth enamel
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Tooth enamel is one of the four major tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the visible part of the tooth, covering the crown. The other major tissues are dentin, cementum, and dental pulp and it is a very hard, white to off-white, highly mineralised substance that acts as a barrier to protect the tooth but can become susceptible to degradation, especially by acids from food and drink. Enamel is the hardest substance in the body and contains the highest percentage of minerals, 96%, with water. The primary mineral is hydroxyapatite, which is a calcium phosphate. Enamel is formed on the tooth while the tooth is developing within the gum, once fully formed, it does not contain blood vessels or nerves. Remineralisation of teeth can repair damage to the tooth to a certain degree, the maintenance and repair of human tooth enamel is one of the primary concerns of dentistry. In humans, enamel varies in thickness over the surface of the tooth, often thickest at the cusp, up to 2.5 mm, the normal color of enamel varies from light yellow to grayish white. At the edges of teeth where there is no dentin underlying the enamel, since enamel is semitranslucent, the color of dentin and any material underneath the enamel strongly affects the appearance of a tooth. The enamel on primary teeth has a more crystalline form. The large amount of mineral in enamel accounts not only for its strength, Tooth enamel ranks 5 on Mohs hardness scale and has a Youngs modulus of 83 GPa. Dentin, less mineralized and less brittle, 3–4 in hardness, Enamel does not contain collagen, as found in other hard tissues such as dentin and bone, but it does contain two unique classes of proteins, amelogenins and enamelins. While the role of proteins is not fully understood, it is believed that they aid in the development of enamel by serving as a framework for minerals to form on. Once it is mature, enamel is almost totally without the softer organic matter, Enamel is avascular and has no nerve supply within it and is not renewed, however, it is not a static tissue as it can undergo mineralization changes. The basic unit of enamel is called an enamel rod, measuring 4–8 μm in diameter, an enamel rod, formally called an enamel prism, is a tightly packed mass of hydroxyapatite crystals in an organized pattern. In cross section, it is best compared to a keyhole, with the top, or head, oriented toward the crown of the tooth, the arrangement of the crystals within each enamel rod is highly complex. Both ameloblasts and Tomes processes affect the crystals pattern, Enamel crystals in the head of the enamel rod are oriented parallel to the long axis of the rod. When found in the tail of the rod, the crystals orientation diverges slightly from the long axis
38.
Copper
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Copper is a chemical element with symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with high thermal and electrical conductivity. A freshly exposed surface of copper has a reddish-orange color. Copper is one of the few metals that occur in nature in directly usable metallic form as opposed to needing extraction from an ore and this led to very early human use, from c.8000 BC. Copper used in buildings, usually for roofing, oxidizes to form a green verdigris, Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as agents, fungicides, and wood preservatives. Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the hemoglobin in fish. In humans, copper is found mainly in the liver, muscle, the adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight. The filled d-shells in these elements contribute little to interatomic interactions, unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This observation explains the low hardness and high ductility of single crystals of copper, at the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is supplied in a fine-grained polycrystalline form. The softness of copper partly explains its high conductivity and high thermal conductivity. The maximum permissible current density of copper in open air is approximately 3. 1×106 A/m2 of cross-sectional area, Copper is one of a few metallic elements with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air, as with other metals, if copper is put in contact with another metal, galvanic corrosion will occur. A green layer of verdigris can often be seen on old structures, such as the roofing of many older buildings. Copper tarnishes when exposed to sulfur compounds, with which it reacts to form various copper sulfides. There are 29 isotopes of copper, 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper, both have a spin of 3⁄2
39.
Steel
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Steel is an alloy of iron and other elements, primarily carbon, that is widely used in construction and other applications because of its high tensile strength and low cost. Steels base metal is iron, which is able to take on two forms, body centered cubic and face centered cubic, depending on its temperature. It is the interaction of those allotropes with the elements, primarily carbon. In the body-centred cubic arrangement, there is an atom in the centre of each cube. Carbon, other elements, and inclusions within iron act as hardening agents that prevent the movement of dislocations that otherwise occur in the lattices of iron atoms. The carbon in steel alloys may contribute up to 2. 1% of its weight. Steels strength compared to pure iron is possible at the expense of irons ductility. With the invention of the Bessemer process in the mid-19th century and this was followed by Siemens-Martin process and then Gilchrist-Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron, further refinements in the process, such as basic oxygen steelmaking, largely replaced earlier methods by further lowering the cost of production and increasing the quality of the product. Today, steel is one of the most common materials in the world and it is a major component in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted standards organizations, the noun steel originates from the Proto-Germanic adjective stakhlijan, which is related to stakhla. The carbon content of steel is between 0. 002% and 2. 1% by weight for plain iron–carbon alloys and these values vary depending on alloying elements such as manganese, chromium, nickel, iron, tungsten, carbon and so on. Basically, steel is an alloy that does not undergo eutectic reaction. In contrast, cast iron does undergo eutectic reaction, too little carbon content leaves iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy, commonly called pig iron, while iron alloyed with carbon is called carbon steel, alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include, manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium. Additional elements are important in steel, phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and copper. Alloys with a higher than 2. 1% carbon content, depending on other element content, cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties
40.
Diamond
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Diamond is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the rate from diamond to graphite is negligible at standard conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material and those properties determine the major industrial application of diamond in cutting and polishing tools and the scientific applications in diamond knives and diamond anvil cells. Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron, small amounts of defects or impurities color diamond blue, yellow, brown, green, purple, pink, orange or red. Diamond also has relatively high optical dispersion, most natural diamonds are formed at high temperature and pressure at depths of 140 to 190 kilometers in the Earths mantle. Carbon-containing minerals provide the source, and the growth occurs over periods from 1 billion to 3.3 billion years. Diamonds are brought close to the Earths surface through deep volcanic eruptions by magma, Diamonds can also be produced synthetically in a HPHT method which approximately simulates the conditions in the Earths mantle. An alternative, and completely different growth technique is chemical vapor deposition, several non-diamond materials, which include cubic zirconia and silicon carbide and are often called diamond simulants, resemble diamond in appearance and many properties. Special gemological techniques have developed to distinguish natural diamonds, synthetic diamonds. The word is from the ancient Greek ἀδάμας – adámas unbreakable, the name diamond is derived from the ancient Greek αδάμας, proper, unalterable, unbreakable, untamed, from ἀ-, un- + δαμάω, I overpower, I tame. Diamonds have been known in India for at least 3,000 years, Diamonds have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early human history, later in 1797, the English chemist Smithson Tennant repeated and expanded that experiment. By demonstrating that burning diamond and graphite releases the same amount of gas, the most familiar uses of diamonds today are as gemstones used for adornment, a use which dates back into antiquity, and as industrial abrasives for cutting hard materials. The dispersion of light into spectral colors is the primary gemological characteristic of gem diamonds. In the 20th century, experts in gemology developed methods of grading diamonds, four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds, these are carat, cut, color, and clarity. A large, flawless diamond is known as a paragon and these conditions are met in two places on Earth, in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike. The conditions for diamond formation to happen in the mantle occur at considerable depth corresponding to the requirements of temperature and pressure
41.
Energy density
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Energy density is the amount of energy stored in a given system or region of space per unit volume. Colloquially it may also be used for energy per unit mass, often only the useful or extractable energy is measured, which is to say that chemically inaccessible energy such as rest mass energy is ignored. In short, pressure is a measure of the enthalpy per unit volume of a system, a pressure gradient has a potential to perform work on the surroundings by converting enthalpy until equilibrium is reached. There are many different types of stored in materials. In order of the magnitude of the energy released, these types of reactions are, nuclear, chemical, electrochemical. Chemical reactions are used by animals to derive energy from food, electrochemical reactions are used by most mobile devices such as laptop computers and mobile phones to release the energy from batteries. The following is a list of the energy densities of commonly used or well-known energy storage materials. Note that this list does not consider the mass of reactants commonly available such as the oxygen required for combustion or the efficiency in use. The following unit conversions may be helpful when considering the data in the table,1 MJ ≈0.28 kWh ≈0.37 HPh. In energy storage applications the energy density relates the mass of a store to the volume of the storage facility. The higher the density of the fuel, the more energy may be stored or transported for the same amount of volume. The energy density of a fuel per unit mass is called the energy of that fuel. The greatest energy source by far is mass itself and this energy, E = mc2, where m = ρV, ρ is the mass per unit volume, V is the volume of the mass itself and c is the speed of light. This energy, however, can be released only by the processes of nuclear fission, nuclear fusion, nuclear reactions cannot be realized by chemical reactions such as combustion. Although greater matter densities can be achieved, the density of a star would approximate the most dense system capable of matter-antimatter annihilation possible. A black hole, although denser than a star, does not have an equivalent anti-particle form. In the case of small black holes the power output would be tremendous. The highest density sources of energy aside from antimatter are fusion and fission, fusion includes energy from the sun which will be available for billions of years but so far, sustained fusion power production continues to be elusive
42.
Electric potential energy
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An object may have electric potential energy by virtue of two key elements, its own electric charge and its relative position to other electrically charged objects. The SI unit of potential energy is the joule. In the CGS system the erg is the unit of energy, also electronvolts may be used,1 eV =1. 602×10−19 J. The following outline of proof states the derivation from the definition of electric potential energy, the electrostatic potential energy UE stored in a system of N charges q1, q2. A common question arises concerning the interaction of a point charge with its own electrostatic potential, since this interaction doesnt act to move the point charge itself, it doesnt contribute to the stored energy of the system. Consider bringing a point charge, q, into its position in the vicinity of a point charge. Some elements in a circuit can convert energy from one form to another, for example, a resistor converts electrical energy to heat. This is known as the Joule effect, a capacitor stores it in its electric field. These latter two expressions are only for cases when the smallest increment of charge is zero such as dielectrics in the presence of metallic electrodes or dielectrics containing many charges
