:: wikimiki.org ::

Scale

Scale

Scale can refer to:
- Scale (computing)
- Scale (map)
- Scale (ratio)
- Scale (spatial)
- Scale (zoology)
- Logarithmic scale, mathematics
- Order of magnitude
- Scale factor
- Duration scale
- Architect's scale - (or draughtsman's scale) is a ruler-like device, which facilitates the production of technical drawings.
- Engineer's scale
- Weighing scale - used for measurement of weight (mass or force)
- Zadok scale cereal development
- Zoology: Scale insect, plant parasites which resemble animal scales
- Geosciences: Mohs scale of mineral hardness
- Atmospheric sciences: Celsius scale, Fahrenheit scale, Kelvin scale, Saffir-Simpson Hurricane Scale, Fujita scale (tornadoes), Beaufort scale (wind)

Astronomy

- Scale factor (Universe)
- Large-scale structure of the cosmos
- Palermo Technical Impact Hazard Scale
- Torino Scale
- Solar flare energy intensity

Chemistry and physics

- Mulliken scale electronegativity
- Hounsfield scale (radiodensity)
- Allred-Rochow scale, Mulliken scale, Pauling scale

Economics

- Scale (economics)
- Resource-Based Relative Value Scale, returns to scale

Music

- Scale (music)
- Bohlen-Pierce scale, chromatic scale, Deutsch's scale illusion, diminished scale, mathematics of musical scales, minor scale

Scale models

- Scale model
- 2 mm scale, HO scale, O scale

Seismology

- European Macroseismic Scale, Japan Meteorological Agency seismic intensity scale, Mercalli Intensity Scale, Moment magnitude scale, Richter magnitude scale

Social science

- Scale (social sciences)
- Likert scale, questionnaire format
- Kinsey scale, sexual orientation (Klein scale is superior but not yet as well known)
- Social stratification, socioeconomic class

Measuring system

Scales with special uses are often named after the person who invented them.
- The Richter scale, the Mercalli scale, the Rossi-Forel scale and the Omori are all used to measure the intensity of earthquakes.
- The Beaufort scale is used to measure wind force.
- The Celsius scale measures the temperature.
- The Goldberg scale measures mania and depression.
- The Scoville Scale measures the hotness of peppers.
- The Glasgow Coma Scale measures the severity of comas.
- The Fujita scale estimates the intensity of tornadoes.
- The Torino scale and the Palermo scale measure the impact hazard level of near-Earth objects such as asteroids.

Miscellaneous

- Chain of being
- Hierarchy
- Time scales: Historical periods, Geologic periods

Scale (computing)

Scale in the computing field is used as a verb. An algorithm, design, networking protocol, program, or other system is said to scale if it is suitably efficient and practical when applied to large situations (e.g. a large input data set or large number of participating nodes in the case of a distributed system). For example, the distributed nature of the Domain Name System allows it to work efficiently even when all hosts on the worldwide Internet are served, so it is said to "scale well". If the design fails when the quantity increases then it does not scale. For example, some early P2P applications, such as Gnutella, had scaling issues as each node broadcast its requests to all peers. This means that the demand on each peer would in the worst case increase in proportion with the total number of peers, potentially quickly overrunning the peers' limited capacity. Other P2P systems like BitTorrent scale well because demand on each peer is independent of the total number of peers.

Scale (ratio)

The concept of scale is applicable if a system is represented proportionally by another system. For example, for a scale model of an object, the ratio of corresponding lengths is a dimensionless scale, e.g. 1:25; this scale is larger than 1:50. In the general case of a differentiable bijection, the concept of scale can, to some extent, still be used, but it may depend on location and direction. It can be described by the Jacobian matrix. The modulus of the matrix times a unit vector is the scale in that direction. The non-linear case applies for example if a curved surface like part of the Earth's surface is mapped to a plane, see map projection. In the case of an affine transformation the scale does not depend on location but it depends in general on direction. If the affine transformation can be decomposed into isometries and a transformation given by a diagonal matrix, we have directionally differential scaling and the diagonal elements (the eigenvalues) are the scale factors in two or three perpendicular directions. For example, on some profile maps horizontal and vertical scale are different; in particular elevation may be shown in a larger scale than horizontal distance. In the case of directional scaling (in one direction only) there is just one scale factor for one direction. The case of uniform scaling corresponds to a geometric similarity. There is just one scale throughout. In the case of an isometry the scale is 1:1. In the more general case of one quantity represented by another one, the scale has also a physical dimension. E.g., if an arrow is drawn to represent a physical vector, the "scale" has a physical dimension equal to that of the vector, divided by length. For example, if a force of 1 newton is represented by an arrow of 2 cm, the scale is 1 m : 50 N. There is typically consistency in scale among quantities of the same dimension, but otherwise scales within the same diagram may vary; e.g "5 m" may also be represented by an arrow of 2 cm; in that case the scale for vectors which represent length is 1:250. Correspondingly, torques could be represented on the same map by areas in a scale of 1 m² : 12 500 Nm, which is equal to 1 m : 12 500 N. Torques in the plane of the map could be represented by arrows with an independent scale of e.g. 1 m : 300 Nm. The scale of a map or enlarged or reduced model indicates the ratio between the distances on the map or model and the corresponding distances in reality or the original. E.g. a map of scale 1:50,000 shows a distance of 50,000 cm (=500 m) as 1 cm on a map, and a model on a scale 1:25 of a building with a height of 30 m has a model height of 1.20 m. An alternative method of indicating the scale is by a scale bar. This can also be applied on a computer screen etc., where the ratio may vary, and also remains valid when enlarging or reducing a paper map.

Scale (spatial)

Spatial scale provides a "shorthand" form for discussing relative lengths, areas, distances and sizes. A microclimate, for instance, is one which might occur in a mountain valley or near a lakeshore, whereas a megatrend is one which involves the whole planet. It is important to realize that these divisions are more or less arbitrary, and where, on this table, mega- is assigned global scope, it may only apply continentally or even regionally in other contexts. The interpretations of meso- and macro- must then be adjusted accordingly.

External links

[http://www.falstad.com/scale/ A sense of scale by Paul Falstad] — visual depictions of the relative scale of various distances, ranging from the Planck length to the furthest known object in the Universe.

Scale (zoology)

In most biological nomenclature, a scale (Greek lepid, Latin squama) is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration. Scales are quite common and have evolved multiple times with varying structure and function. Fish scales are bony and covered with a smooth transparent tegument to improve the flow of water over them. Reptile scales are more like fingernail. Birds also have scales, commonly on their feet, and their feathers are thought to have been derived from modified scales. A few mammals also have scales, such as the pangolin, and these are originally derived from hair. There are various types of scales according to shape and class. The scales of bony fishes are laid head to tail, reducing drag.

Cosmoid scales

True cosmoid scales can only be found on the extinct Crossopterygians. The inner layer of the scale is made of compact bone. On top of this lies a spongy layer and then a layer of dentinelike material called cosmine. The upper surface is keratin. The coelacanth has modified cosmoid scales, that are thinner than true cosmoid scales.

Ganoid scales

Ganoid scales can be found on gars (family Lepisosteidae) and bichirs and reedfishes (family Polypteridae). Ganoid scales are similar to cosmoid scales, but a layer of ganoin lies over the cosmine layer and under the enamel. They are diamond-shaped, shiny, and hard.

Placoid scales

Placoid scales are found on cartilaginous fish and sharks. These scales, also called denticles, are similar in structure to teeth.

Ctenoid and cycloid scales

Ctenoid which have a toothed outer edge, and are usually found on fishes with spiny fin rays, such as bass and crappie. Cycloid scales have a smooth outer edge, and are most common on fish with soft fin rays, such as salmon and carp. As they grow, cycloid and ctenoid scales add concentric layers.

Lepidopteran wing scales

carp Butterfly and moth species of the order Lepidoptera (Greek "scale-winged") have membranous wings covered in delicate, powdery scales. Each scale consists of a series of tiny stacked platelets of organic material. Because the thickness of the platelets is on the same order as the wavelength of visible light the plates lead to structural coloration and iridescence through the physical phenomenon described as thin-film optics.

Others

Reptile scale types include: cycloid, granular (which appear bumpy), and keeled (which have a center ridge). Category:Integumentary system ja:鱗

Logarithmic scale

A logarithmic scale is a scale of measurement that uses the logarithm of a physical quantity instead of the quantity itself. Presentation of data on a logarithmic scale can be helpful when the data covers a large range of values; the logarithm reduces this to a more manageable range. Some of our senses operate in a logarithmic fashion (doubling the input strength adds a constant to the subjective signal strength), which makes logarithmic scales for these input quantities especially appropriate. In particular our sense of hearing perceives equal ratios of frequencies as equal differences in pitch. Logarithmic scales are either defined for ratios of the underlying quantity, or one has to agree to measure the quantity in fixed units. Deviating from these units means that the logarithmic measure will change by an additive constant. The base of the logarithm also has to be specified, unless the scale's value is considered to be a dimensional quantity expressed in generic (indefinite-base) logarithmic units. On most logarithmic scales, small values (or ratios) of the underlying quantity correspond to small (possibly negative) values of the logarithmic measure. Well-known examples of such scales are:
- Richter magnitude scale for strength of earthquakes and movement in the earth.
- bel and decibel and neper for acoustic power (loudness) and electric power;
- cent, minor second, major second, and octave for the relative pitch of notes in music;
- logit for odds in statistics;
- Palermo Technical Impact Hazard Scale;
- Logarithmic timeline;
- counting f-stops for ratios of photographic exposure;
- rating low probabilities by the number of 'nines' in the decimal expansion of the probability of their not happening: for example, a system which will fail with a probability of 10^-5 is 99.999% reliable: "five nines".
- Entropy in thermodynamics.
- Information in information theory. Some logarithmic scales were designed such that large values (or ratios) of the underlying quantity correspond to small values of the logarithmic measure. Examples of such scales are:
- pH for acidity;
- stellar magnitude scale for brightness of stars;
- Krumbein scale for grain size in geology.
- Kardashev scale for technological advance in physics.

Graphic representation

A logarithmic scale is also a graphic scale on one or both sides of a graph where a number x is printed at a distance c·log(x) from the point marked with the number 1. A slide rule has logarithmic scales, and nomograms often employ logarithmic scales. On a logarithmic scale an equal difference in order of magnitude is represented by an equal distance. The geometric mean of two numbers is midway between the numbers. Logarithmic graph paper, before the advent of computer graphics, was a basic scientific tool. Plots on paper with one log scale can show up exponential laws, and on log-log paper power laws, as straight lines. Category:Scales

Scale factor

A scale factor is a number which scales some quantity. For example, doubling distances corresponds to a scale factor of 2 for distance. There is also a scale factor for the expansion of the Universe.

Duration scale

:For other meanings of duration, see: duration (disambiguation). A duration is an amount of time or a particular time interval. For example, an event in the common sense has a duration greater than zero (but not very long), but in certain specialised senses, a duration of zero. It is often cited as one of the fundamental aspects of music, see also rhythm. Durations, and their beginnings and endings, may be described as long, short, or taking a specific amount of time. Often duration is described according to terms borrowed from descriptions of pitch. As such, the duration complement is the amount of different durations used, the duration scale is an ordering (scale) of those durations from shortest to longest, the duration range is the difference in length between the shortest and longest, and the duration hierarchy is an ordering of those durations based on frequency of use (DeLone et. al. (Eds.), 1975, chap. 3). Durational patterns are the foreground details projected against a background metric structure, which includes meter, tempo, and all rhythmic aspects which produce temporal regularity or structure. Duration patterns may be divided into rhythmic units and rhythmic gestures. (DeLone et. al. (Eds.), 1975, chap. 3) However, they may also be described using terms borrowed from the metrical feet of poetry: iamb (weak-strong), anapest (weak-weak-strong), trochee (strong-weak), dactyl (strong-weak-weak), and amphibrach (weak-strong-weak), which may overlap to explain ambigouity (Cooper and Meyer, 1960). See also: time scale.

Sources

- Cooper and Meyer (1960). The Rhythmic Structure of Music. University of Chicago Press. ISBN 0226115224. Cited in Delone directly below.
- DeLone et. al. (Eds.) (1975). Aspects of Twentieth-Century Music. Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 0130493465. Category:Aspects of music

Architect's scale

An architect's scale is a specialized ruler. It is used in making or measuring from reduced scale drawings, such as blueprints. It is marked with a range of calibrated scales (ratios). The scale was traditionally made of wood but for accuracy and longevity the material used should be dimensionally stable and durable. Today they are now more commonly made of rigid plastic or aluminium. Depending on the number of different scales to be accommodated architect's scales may be flat or shaped with a cross-section of an equilateral triangle.

United States and Imperial units

In the United States, and prior to metrification in Britain, Canada and Australia, architect's scales are/were marked as a ratio of x inches-to-the-foot. For example one inch measured from a drawing with a scale of "one-inch-to-the-foot" is equivalent to one foot in the real world (a scale of 1:12) whereas one inch measured from a drawing with a scale of "two-inches-to-the-foot" is equivalent to six inches in the real world (a scale of 1:6). Typical scales used in the United States are:
- Full scale, with inches divided into sixteenths of an inch The following scales are generally grouped in pairs using the same dual-numbered index line:
- three-inches-to-the-foot (1:4) / one-and-one-half-inch-to-the-foot (1:8)
- two-inches-to-the-foot (1:6) / one-inch-to-the-foot (1:12)
- three-quarters-inch-to-the-foot (1:16) / three-eighths-inch-to-the-foot (1:32)
- one-half-inch-to-the-foot (1:24) / one-quarter-inch-to-the-foot (1:48)
- one-eighths-inch-to-the-foot (1:96) / one-sixteenths-inch-to-the-foot (1:192)

Metric units

Architect's scale rulers used in Britain and other metric areas are marked with ratios without reference to a base unit. Therefore a drawing will indicate both its scale and the unit of measurement being used. In Britain the standard units used on architectural drawings are the SI units millimetres (mm) and metres (m), whereas in France centimetres (cm) and metres are most often used. In Britain, for flat rulers, the paired scales often found on architect's scales are:
- 1:1 / 1:100
- 1:5 / 1:50
- 1:20 / 1:200
- 1:1250 / 1:2500 and for triangular rulers:
- 1:1 / 1:10
- 1:2 / 1:20
- 1:5 / 1:50
- 1:100 / 1:200
- 1:500 / 1:1000
- 1:1250 / 1:2500

Engineer's scale

An engineer's scale is a ruler, a tool for measuring distances. It is commonly made of plastic and is just over twelve inches long, so that the measuring ticks at the edges do not become unusable by wearage. It is used in making engineering drawings, commonly called blueprints, in scale. For example, "one-tenth size" would appear on a drawing to indicate a part larger than the paper itself. It is not to be used to measure the machined parts to see if these meet the specifications. This scale is divided into decimalized fractions of an inch, but has a cross-section like an equilateral triangle, which enables the scale to have six edges indexed for measurement. One edge is divided into tenths of an inch, and the subsequent ones are directly marked for twentieths, thirtieths, fortieths, fiftieths, and finally sixtieths of an inch. On a metric engineer's scale, common scales are 1:100, 1:200, 1:250, 1:300, 1:400, and 1:500. The engineer's scale came into existence when machining parts required a greater precision than the usual, binary fractionalization of the inch as in the architect's scale for houses and furniture. They were used, for example, in laying out printed circuit boards with the spacing of leads from integrated circuit chips as one-tenth of an inch. In the twenty-first century, those which are commonly purchased in the US are actually made in Germany.

Weighing scale

A weighing scale (usually just "scale" in common usage) is a device using for measuring the weight of an object. These scales are often used to measure the weight of a person, and are also used in science to obtain the mass of an object, and in many industrial and commercial applications to determine the weight of things ranging from feathers to loaded tractor-trailers. Weighing scales are also sometimes used to measure force rather than mass.

Balances

A balance (also balance scale, beam balance or laboratory balance) is used to accurately measure the mass of an object. This class of measuring instrument uses a comparison technique in its conventional form of a beam from which a weighing pan (weighing bason) and scale pan (scale bason) are suspended. To weigh an object, it is placed on the measuring pan, and standard weights are added to the scale pan until the beam is in equilibrium. Very precise measurements are achieved by ensuring that the fulcrum of the beam is friction-free (a knife edge is the traditional solution), by attaching a pointer to the beam which amplifies any deviation from a balance position; and finally by using the lever principle, which allows fractional weights to be applied by movement of a small weight along the measuring arm of the beam. While the word "weigh" or "weight" is often used, any balance scale actually measures mass, which is not dependent upon the force of gravity. The moments of force on either side balance, and the acceleration of gravity on each side cancels out, so a change in the strength of the local gravitational field will not change the measured weight. Mass is properly measured in grams, kilograms, pounds, ounces, or slugs. The original form of weighing scale consisted of a beam with a fulcrum at its center. For highest accuracy the fulcrum would consist of a sharp V-shaped pivot seated in a shallower V-shaped bearing. To determine the mass of the object, a combination of reference weights was hung on one end of the beam while the object of unknown mass was hung on the other end. See balance and steelyard. For high precision work the center beam balance is still one of the most accurate technologies available, and is commonly used for calibrating test weights. In order to reduce the need for large reference weights an off-center beam can be used. This design can be almost as accurate as the center beam, but requires special reference weights and cannot be intrinsically checked for accuracy by simply swapping the contents of the pans, as a center-beam balance can. To reduce the need for small graduated reference weights a sliding weight, called a poise, can be installed so that it can be positioned along a calibrated scale. This adds further intricacies to the calibration procedure, since the exact mass of the poise must be adjusted to the exact lever ratio of the beam. For greater convenience in placing large and awkward loads, a platform can be "floated" on a cantilever beam system which brings the proportional force to a "noseiron" bearing; this pulls on a "stilyard rod" to transmit the reduced force to a conveniently sized beam. One still sees this design in "portable beam scales" of 1000 lb / 500 kg capacity which are commonly used in harsh environments where electricity is not available, as well as in the lighter duty mechanical bathroom scale. The additional pivots and bearings all reduce the accuracy and complicate calibration; the float system must be corrected for corner errors before span is corrected by adjusting the balance beam and poise. Such systems are typically accurate to at best 1/10,000 of their capacity, unless they are very expensively engineered. Some expensive mechanical scales also use dials with counterbalancing weights instead of springs, a hybrid design with some of the accuracy advantages of the poise and beam but the convenience of a dial reading. These designs are expensive to produce and are largely obsolete thanks to electronics.

Spring scales

steelyard Some weighing scales such as a Jolly balance (named after Phillipp Gustav von Jolly who invented the balance about 1874) use a spring with a known spring constant (see Hooke's law) and measure the displacement of the spring by any variety of mechanisms to produce an estimate of the gravitational force applied by the object, which can be simply hung from the spring or set on a pivot and bearing platform. Rack and pinion mechanisms are often used to convert the linear spring motion to a dial reading. Spring scales typically measure force, which can be measured in units of force such as newtons or pounds-force. Spring scales typically cannot be used for commercial applications unless their springs are temperature compensated or used at a fairly constant temperature. The spring scales which are legal for commerce can be calibrated for the accurage measurement of mass (the quantity measured for weight in commerce) in the location in which they are used. They can give an accurate measurement in kilograms or pounds for this purpose.

Hydraulic or pneumatic scales

It is also common in high-capacity applications such as crane scales to use hydraulic force to sense weight. The test force is applied to a piston or diaphragm and transmitted through hydraulic lines to a dial indicator based on a Bourdon tube or electronic sensor.

Testing and certification

Most countries regulate the design and servicing of scales used for commerce. This has tended to cause scale technology to lag behind other technologies because expensive regulatory hurdles are involved in introducing new designs. Nevertheless, there has been a recent trend to "digital load cells" which are actually strain-gage cells with dedicated analog converters and networking built into the cell itself. Such designs have reduced the service problems inherent with combining and transmitting a number of 20 millivolt signals in hostile environments. Government regulation generally requires periodic inspections by licensed technicians using weights whose calibration is traceable to an approved laboratory. Scales intended for casual use such as bathroom or diet scales may be produced, but must by law be labelled "Not Legal for Trade" to ensure that they are not repurposed in a way that jeopardizes commercial interest. In the United States, the document describing how scales must be designed, installed, and used for commercial purposes is NIST Handbook 44.

Laboratory balances

NIST A balance (also beam balance or laboratory balance) is used to accurately measure the mass of an object. This class of measuring instrument uses a comparison technique in its conventional form of a beam from which a weighing pan and scale pan are suspended. To weigh an object, it is placed on the measuring pan, and standard weights are added to the scale pan until the beam is in equilibrium. While the word "weigh" or "weight" is often used, any balance scale actually measures mass, which is not dependent upon the force of gravity, as opposed to a scale with a spring, which measures weight. Mass is properly measured in grams, kilograms, pounds, ounces, or slugs; while weight is in newtons or pound force. An analytical balance is an instrument used to measure mass to a very high degree of precision. The weighing pan(s) of a high accuracy (0.1 mg or better) analytical balance are inside a see-through enclosure with doors so dust does not collect and so any air currents in the room do not affect the delicate balance. Also, the sample must be at room temperature to prevent natural convection from forming air currents inside the enclosure, affecting the weighing. Very precise measurements are achieved by ensuring that the fulcrum of the beam is friction-free (a knife edge is the traditional solution), by attaching a pointer to the beam which amplifies any deviation from a balance position; and finally by using the lever principle, which allows fractional weights to be applied by movement of a small weight along the measuring arm of the beam. See [http://www.dartmouth.edu/~chemlab/techniques/a_balance.html Analytical Balance article at ChemLab]

External links

- National Conference on Weights and Measures, NIST Handbook 44, [http://ts.nist.gov/ts/htdocs/230/235/h44.htm Specifications, Tolerances, And Other Technical Requirements for Weighing and Measuring Devices], 2000
- [http://www.scalemanufacturer.com body fat scale,kitchen scale]
- [http://ohaus.com O'haus Balances]
- [http://www.wolflabs.co.uk/Balances%20switchboard%201.htm Balances from Denver Instruments] Category:Measuring instruments Category:Mass

Weight

:See also weight function. For the 1994 album by the group Rollins Band, see Weight (album). In the physical sciences, weight is the interaction of matter with a gravitational field. It is equal to the mass of the object multiplied by the magnitude of the gravitational field. The word weight entered Old English sometime around the 9th century, and meant the quantity measured with a balance -- the same as mass in both common and scientific usage. In common usage, weight still means the same as mass.

Weight and mass

"Weight" is often used as a synonym for mass. For instance, when we buy or sell goods "by weight", we are interested in the amount of goods exchanged, not how hard it presses down on the table. Similarly, in measurements of body weight we are primarily interested in the amount of tissue (fat, muscle, etc.) present. Correspondingly, weight is often given in kilograms and other units of mass. In the physical sciences, people usually distinguish between weight and mass. Under most circumstances, this ambiguity is not a problem, because the weight of an object is directly proportional to its mass, and the constant of proportionality -- the strength of the gravitational field -- is approximately constant everywhere on the surface of the Earth (around 9.8 m/s²). For instance, a body will exert less force if it is located on the Moon than if it is on the Earth, since the gravitational field of the Moon is weaker; its mass, on the other hand, does not depend on position. Although terms such as "atomic weight", "molecular weight", and "formula weight" may still be encountered, such usage is often discouraged; terms like atomic mass are used instead. Mass is measured using a balance which compares an item in question to matter of known mass; this method is independent of gravity. Alternately, a spring scale or Hydraulic or pneumatic scale is used to measure force (which physicists call weight). Most scales measure weight using a spring. Related to the historical identification of mass and weight, the pound has been used both as a unit of mass and as a unit of force. In the United States, United Kingdom, and elsewhere, the pound is and always has been officially defined as a unit of mass. The corresponding force is called a pound-force, and similarly the weight of a kilogram of material on Earth is called a kilogram-force. However, the use of pounds to measure forces is still common in engineering, and it occurs in derived units like p.s.i. (pounds per square inch). In most countries, scientists have adopted SI units, which use kilogram for mass and newton for force non-interchangeably.

Weight as a force

The SI unit for weight is the newton (N), or kilogram metres per second squared (kg m s⁻²). The weight force that we sense is actually the normal force exerted by the surface we stand on, which prevents us from being pulled to the center of the Earth, and not the weight itself. This normal force, that we can call the apparent weight is the one that is measured by a weighing scale, not the weight itself. A good evidence of this is given by the fact that a person moving up and down on his toes does see the indicator moving, telling that the measured force is changing while his weight, that depends only on his mass, the Earth mass and the distance between his center of mass and the center of Earth obviously do not change. In contrast, in free-fall, there is no apparent weight because we are not in contact with any surface to provide such a normal force. The experience of having no apparent weight is known as weightlessness or microgravity.

Comparative weights on bodies of the solar system

The following is a list of the weights of a mass on some of the bodies in the solar system, relative to its weight on Earth: For weight variations on Earth, see gee, physical geodesy and gravity anomaly.

Human weight in the medical sciences and ordinary language

Although many people prefer the less-ambiguous term body mass to body weight, the term weight is overwhelmingly used in daily English speech and in biological and medical science contexts. Body weight is measured in kilograms throughout the world. Most hospitals in the United States use kilograms for calculations, but use kilograms and pounds simultaneously for other purposes (a pound is 0.45 kg). Many people in the United Kingdom still measure their weight using the stone equal to 14 lb (6.35 kg).

Sports usage

Participants in sports such as boxing, wrestling, judo, and weight-lifting are classified according to their body weight, measured in units of mass such as pounds or kilograms. See, e.g., wrestling weight classes, boxing weight classes, judo at the 2004 Summer Olympics, boxing at the 2004 Summer Olympics. In horse racing, weight is used to handicap horses. A weight also refers to the physical objects used in weight-lifting and other sports such as the hammer throw.

Force

:For other senses of this word, see force (disambiguation). In physics, a force is an external cause responsible for any change of a physical system. For instance, a person holding a dog by a rope is experiencing the force applied by the rope on their hand, and the cause for its pulling forward is the force exercised by the rope. The kinetic expression of this change is, according to Newton's second law, acceleration, non kinetic expressions such as deformation can also occur. The SI unit for force is the newton.

Elementary concepts

Force in its most primitive definition can be thought of as that which when acting alone causes an object to accelerate. In a practical sense forces can be divided into two groups: contact forces and field forces. Contact forces require the physical contact of one object with other such as a hammer striking a nail or the force exerted by a gas under pressure - gas produced by exploding gunpowder forces a heavy ball out of a cannon. Field forces on the other hand need no physical medium of contact. Gravity and magnetism are examples of such forces. It should be noted however, that fundamentally all forces are in fact field forces. The force of hammer striking the nail in the previous example turns out to be a clash of the electric forces in both hammer and nail. Nevertheless it is appropriate in some cases to maintain these two classifications for ease of understanding.

Quantitative definition

In physics models, the point-like system is used, where objects are represented as one-dimensional points at their centre of mass. The only change the system can experience is a change of its momentum (its speed). Since the rise of the atomic theory, any physical system has been considered in classical physics as composed of point-like systems called atoms or molecules. Therefore, all forces can be defined by their effect; that is, by the change of movement they induce on point-like systems. This change of movement can be quantified by the acceleration (the derivative of velocity). The discovery by Isaac Newton that a given force will induce an acceleration in inverse proportion to a quantity called the mass of inertia or inertial mass which is independent of the speed of the system is Newton's second law. This law allows us to predict the effect of a force on any point-like system whose mass is known. It is usually written as: :F = dp/dt = d(m·v)/dt = m·a (in the case where m does not depend on t) where :F is the force (a vector quantity), :p is the momentum, :t is the time, :v is the velocity, :m is the mass, and :a=d²x/dt² is the acceleration, the second derivative with respect to t of the position vector x. If the mass m is measured in kilograms and the acceleration a is measured in metres per second squared, then the unit of force is kilogram × metre/second squared. This unit is called the newton: 1 N = 1 kg x 1 m/s². This equation is a system of three second-order differential equations with respect to the three-dimensional position vector which is an unknown function of time. This equation can be solved if F is a known function of x and some of its derivatives and if the mass m is known. Morevover the boundary conditions are required; for example, the values of the position vector and x and the velocity v at the starting time, say t=0. Of course, this formula is only useful if one knows the numerical values of F and m. The definition above is an implicit definition, arrived at as follows. One defines a reference system (one litre of water) and a reference force (the gravitational force applied by the Earth on it at the altitude of Paris). One takes Newton's second law for granted (one postulates that it is true) and measures the acceleration induced by the reference force on the reference system. This gives us a mass unit (1 kg) and a force unit (the older unit of 1 kilogram-force = 9.81 N). Once this is done, one can measure any force by the acceleration it induces on the reference system and measure the inertial mass of any system by measuring the acceleration induced on this system by the reference force. Force is often considered a fundamental quantity in physics, but there are more fundamental quantities, such as momentum (p = mass m x velocity v). Energy, measured in joules, is still less fundamental than force and momentum, because it is defined as work, and work is defined in terms of force. The two most fundamental theories of nature - quantum electrodynamics and general relativity - do not contain the concept of force at all. Although not the most fundamental quantity in physics, force is an important basic mathematical concept from which other concepts, such work and pressure (measured in pascals), are derived. Force is sometimes confused with stress.

Types of force

There are four known fundamental forces in nature.
- Nuclear forces acting between subatomic particles
- Electromagnetic forces between electric charges
- Weak forces arising from radioactive decay
- Gravitational forces between masses Quantum field theory accurately models the first three fundamental forces, but does not model quantum gravity. Quantum gravity on a large scale can, however, be described by general relativity. The four fundamental forces describe every observable phenomenon including the many other forces observed such as: Coulomb's force (the force between electrical charges), gravitational force (force between masses), magnetic force, frictional forces, centripetal, centrifugal, impact force, and spring force, to name a few. Forces can also be classified into conservative forces and nonconservative forces. Conservative forces are equivalent to the gradient of a potential, and include gravity, electromagnetic force, and spring force. Nonconservative forces include friction and drag.

Properties of force

Because momentum is a vector, then force, being its time derivative, is also a vector - it has magnitude and direction. Forces can be added together using the parallelogram of force. When two forces act on an object, the resulting force, the resultant, is the vector sum of the original forces. This is called the principle of superposition. The magnitude of the resultant varies from zero to the sum of the magnitudes of the two forces, depending on the angle between their lines of action. If the two forces are equal, but opposite, the resultant is zero. This condition is called static equilibrium, with the result that the object remains at rest or moves with a constant velocity. As well as being added, forces can be can also be broken down (or 'resolved'). For example, a horizontal force pointing northeast can be split into two forces, one pointing north, and one pointing east. Summing these component forces using vector addition yields the original force. Force vectors can also be three-dimensional, with the third (vertical) component at right-angles to the two horizontal components.

Forces in theory

The total (Newtonian) force, in newtons, on an object at any given time is defined as the rate of change of the object's velocity multiplied by the object's mass: :

\mathbf = \lim_ \frac

where :m is the inertial mass of the particle (measured in kilograms) :v_o is its initial velocity (measured in metres per second) :v is its final velocity (measured in metres per second) :T is the time from the initial state to the final state (measured in seconds); :Lim T→0 is the limit as T tends towards zero. Force was so defined to explain the effects of superimposing situations: if in one situation, a force is experienced by a particle, and if in another situation another force is experienced by that particle, then in a third situation, which (according to standard physical practice) is taken to be a combination of the two individual situations, the force experienced by the particle will be the vector sum of the individual forces experienced in the first two situations. This superposition of forces, and the definition of inertial frames and inertial mass, are the empirical content of Newton's laws of motion. There are other ways to look at the above definition of force. First, the mass of a body multiplied by its velocity is called its momentum, p, so the above definition is equivalent to: :

\textbf=

If F is not constant over Δt, then this is the definition of average force over the time interval. To apply it at an instant we apply an idea from calculus. If we graph p as a function of time, the average force will be the slope of the line connecting the momentum at two times. Taking the limit as the two times get closer together gives the slope at an instant, which is called the derivative: :

\textbf=

Many forces are associated with a potential energy field. For instance, the gravitational force acting upon a body can be seen as the action of the gravitational field that is present at the body's location. The potential field is defined as that field whose gradient is equal and opposite to the force produced at every point: :

\textbf=-\nabla U

The derivative of force with respect to time is called yank. Higher order derivatives are sometimes used, but they lack names because of their rarity. In most explanations of mechanics, force is usually defined only implicitly, in terms of the equations that work with it. Some physicists, philosophers and mathematicians, such as Ernst Mach, Clifford Truesdell and Walter Noll, have found this problematic and sought a more explicit definition of force. According to the Special theory of relativity the mass of an object increases as it's velocity and therefore it's energy increases. The law of force must then be modified to the following: :

\textbf=

where :v is the mass's velocity :c is the speed of light. Note that the equation is undefined if the mass's speed is equal to c because one then has to divide by zero. This is one reason most physicists believe an object with nonzero rest mass can not be accelerated to the speed of light, as this would require an infinite force.

Units of measurement

The SI unit used to measure force is the newton (symbol N), which is equivalent to kg·m·s⁻².

Non-SI units of force and mass

The F=m·a relationship can be used with any consistent units (SI or CGS). If these units are not consistent, a more general form, F=k·m·a, can be used, where the constant k is a conversion factor dependent upon the units being used. For example, in imperial engineering units, F is measured in "pounds force" or "lbf", m in "pounds mass" or "lb", and a in feet per second squared. In this particular system, one needs to use the more general form above, usually written F=m·a/g_c with the constant normally used for this purpose g_c = 32.174 lb·ft/(lbf·s²) equal to the reciprocal of the k above. As with the kilogram, the pound is colloquially used as both a unit of mass and a unit of force. 1 lbf is the force required to accelerate 1 lb at 32.174 ft per second squared, since 32.174 ft per second squared is the standard acceleration due to terrestrial gravity. Another imperial unit of mass is the slug, defined as 32.174 lb. It is the mass that accelerates by one foot per second squared when a force of one lbf is exerted on it. When the standard gee (an acceleration of 9.80665 m/s²) is used to define pounds force, the mass in pounds is numerically equal to the weight in pounds force. However, even at sea level on Earth, the actual acceleration of free fall is quite variable, over 0.53% more at the poles than at the equator. Thus, a mass of 1.0000 lb at sea level at the equator exerts a force due to gravity of 0.9973 lbf, whereas a mass of 1.000 lb at sea level at the poles exerts a force due to gravity of 1.0026 lbf. The normal average sea level acceleration on Earth (World Gravity Formula 1980) is 9.79764 m/s², so on average at sea level on Earth, 1.0000 lb will exerts a force of 0.9991 lbf. The equivalence 1 lb = 0.453 592 37 kg is always true, by definition, anywhere in the universe. If you use the standard gee which is official for defining kilograms force to define pounds force as well, then the same relationship will hold between pounds-force and kilograms-force (an old non-SI unit is still used). If a different value is used to define pounds force, then the relationship to kilograms force will be slightly different—but in any case, that relationship is also a constant anywhere in the universe. What is not constant throughout the universe is the amount of force in terms of pounds-force (or any other force units) which 1 lb will exert due to gravity. By analogy with the slug, there is a rarely used unit of mass called the "metric slug". This is the mass that accelerates at one metre per second squared when pushed by a force of one kgf. An item with a mass of 10 kg has a mass of 1.01972661 metric slugs (= 10 kg divided by 9.80665 kg per metric slug). This unit is also known by various other names such as the hyl, TME (from a German acronym), and mug (from metric slug). Another unit of force called the poundal (pdl) is defined as the force that accelerates 1 lbm at 1 foot per second squared. Given that 1 lbf = 32.174 lb times one foot per second squared, we have 1 lbf = 32.174 pdl. The kilogram-force is a unit of force that was used in various fields of science and technology. In 1901, the CGPM improved the definition of the kilogram-force, adopting a standard acceleration of gravity for the purpose, and making the kilogram-force equal to the force exerted by a mass of 1 kg when accelerated by 9.80665 m/s². The kilogram-force is not a part of the modern SI system, but is still used in applications such as:
- Thrust of jet and rocket engines
- Spoke tension of bicycles
- Draw weight of bows
- Torque wrenches in units such as "meter kilograms" or "kilogram centimetres" (the kilograms are rarely identified as units of force)
- Engine torque output (kgf·m expressed in various word orders, spellings, and symbols)
- Pressure gauges in "kg/cm²" or "kgf/cm²" In colloquial, non-scientific usage, the "kilograms" used for "weight" are almost always the proper SI units for this purpose. They are units of mass, not units of force. The symbol "kgm" for kilograms is also sometimes encountered. This might occasionally be an attempt to disintinguish kilograms as units of mass from the "kgf" symbol for the units of force. It might also be used as a symbol for those obsolete torque units (kilogram-force metres) mentioned above, used without properly separating the units for kilogram and metre with either a space or a centered dot.

Conversions

Below are several coversion factors between various mesurements of force:
- 1 kgf (kilopond kp) = 9.80665 newtons
- 1 metric slug = 9.80665 kg
- 1 lbf = 32.174 poundals
- 1 slug = 32.174 lb
- 1 kgf = 2.2046 lbf

Forces in everyday life

Forces are part of everyday life, with examples such as:
- gravity: objects fall, even after being thrown upwards, or slide and roll down
- friction: floors and objects that are not extremely slippery
- spring force, objects resist tensile stress, compressive stress and/or shear stress, objects bounce back.
- electromagnetic force: attraction of magnets
- movement created by force: the movement of objects when force is applied.

Forces in the laboratory

Founding experiments

- Galileo Galilei used rolling balls to disprove the Aristotelian theory of motion (1602 - 1607)
- Henry Cavendish's torsion bar experiment measured the force of gravity between two masses (1798)

Instruments to measure forces

- spring balance
- pivot balance
- forcemeter

History

Force was first described by Archimedes.

References

-
-
-

External links

- [http://jumk.de/calc/force.shtml Calculation: force F - English and American units to metric units]
- [http://calc.skyrocket.de/en/ Online Unit Converter - Conversion of many different units]
- [http://www.patbelford.com/gallery/web3d/education/forceworkpower/index.html Interactive demonstration of Force-Work-Power Relationship] Category:Introductory physics ko:힘 ms:Daya (fizik) ja:力 simple:Force (physics)

Zadok scale

The Zadoks scale is a cereal development scale proposed by the Dutch phytopathologist Jan C. Zadoks that is widely used in cereal research and agriculture. Knowing the stages of development of a crop is critical in many management decisions that growers make. They are represented on a scale from 10 to 92. For example, in some countries, nitrogen and herbicide applications must be completed during the tillering stage. In France, the recommendation for the first nitrogen application on wheat is 6 weeks before Z30, with the second application on Z30. Wheat growth regulators are typically applied at Z30. Disease control is most critical in the stem extension and heading stage (Z31, Z32, Z35), in particular as soon as the flag leaf is out (Z37). The crop is also more sensitive to heat or frost at some stages than others (for example, during the meiosis stage the crop is very sensitive to low temperature). Knowing the growth stage of the crop when checking for problems is essential for deciding which control measures should be followed. Examples of typical stages
- during tillering
- Z10: one leaf
- Z21: tillering begins
- during stem extension
- Z30: ear is one centimeter long in wheat
- Z31: first node visible
- Z32: second node visible
- Z37: flag leaf
- during heading
- Z55: the head is 1/2 emerged.
- during ripening
- Z92: grains are ripe Another cereal development scale is the Feekes scale.

Literature

- J.C. Zadoks, T.T. Chang, C.F. Konzak, "A Decimal Code for the Growth Stages of Cereals", Weed Research 1974 14:415-421.

External links

- [http://www.garfield.library.upenn.edu/classics1985/A1985ARS2000001.pdf Citation Classic of 1985] Category:Cereals

Mohs scale of mineral hardness

Mohs' scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. It was created, in 1812, by the German mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science. Mohs based the scale on ten minerals that are all readily available except the last one, diamond. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, and/or the softest material that can scratch the given material. For example, if some material is scratched by apatite but not by fluorite, its hardness on Mohs scale is 4.5. The table below shows comparison with absolute hardness measures by a sclerometer. Mohs' is a purely ordinal scale with, for example, corundum being twice as hard as topaz, but diamond, almost four times as hard as corundum. On the Mohs scale, fingernail has hardness 2; copper penny, about 3; a knife blade, 5; window glass, 5.5; steel file, 6.5. Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale. Some mnemonics traditionally taught to geology students to remember this table are "The Girls Can Flirt And Other Queer Things Can Do" or "To Get Candy From Aunt Fanny, Quit Teasing Cousin Danny". An alternative table is shown below which has been modified to incorporate additional substances that may fall in between two levels. Source: [http://www.amfed.org/t_mohs.htm American Federation of Mineralogical Societies: Mohs Scale of Mineral Hardness] Category:Materials science Category:Mineralogy Category:Scales ja:モース硬度

Fahrenheit scale

Fahrenheit is a temperature scale named after the German physicist Gabriel Fahrenheit (1686–1736), who proposed it in 1724. In this scale, the freezing point of water is 32 degrees (this is written "32 °F"), and the boiling point is 212 degrees Fahrenheit, placing the boiling and melting points of water 180 degrees apart. Thus the unit of this scale, a degree Fahrenheit, is 5/9ths of a kelvin (which is a degree Celsius), and minus 40 degrees Fahrenheit is equal to minus 40 degrees Celsius.

History

There are several competing versions of the story of how Fahrenheit came to devise his temperature scale. One states that Fahrenheit established the zero (0 °F) and 100 °F points on his scale by recording the lowest outdoor temperatures he could measure, and his own body temperature. He took as his zero point the lowest temperature he measured in the harsh winter of 1708 through 1709 in his home town of Gdańsk (Danzig) (-17.8 °C). (He was later able to reach this temperature under laboratory conditions using a mixture of ice, ammonium chloride and water.) Fahrenheit wanted to avoid the negative temperatures which Ole Rømer's scale had produced in everyday use. Fahrenheit fixed his own body temperature as 100 °F (normal body temperature is closer to 98.6 °F, suggesting that Fahrenheit was suffering a fever when he conducted his experiments or that his thermometer was not very accurate), and divided his original scale into twelve divisions; later dividing each of these into 8 equal subdivisions produced a scale of 96 degrees. Fahrenheit noted that his scale placed the freezing point of water at 32 °F and the boiling point at 212 °F, a neat 180 degrees apart. Another holds that Fahrenheit established the zero of his scale (0 °F) as the temperature at which an equal mixture of ice and salt melts (some say he took that fixed mixture of ice and salt that produced the lowest temperature); and ninety-six degrees as the temperature of blood (he initially used horse blood to calibrate his scale). Initially, his scale only contained 12 equal subdivisions, but later he subdivided each division into 8 equal degrees ending up with 96. He then observed that plain water would freeze at 32 degrees and boil at 212 degrees. A third well-known version of the story, as described in the popular physics television series The Mechanical Universe, holds that Fahrenheit simply adopted Rømer's scale, at which water freezes at 7.5 degrees, and multiplied each value by 4 in order to eliminate the fractions and increase the granularity of the scale (giving 30 and 240 degrees). He then re-calibrated his scale between the freezing point of water and normal human body temperature (which he took to be 96 degrees); the freezing point of water was adjusted to 32 degrees so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power). His measurements were not entirely accurate, though; by his original scale, the actual freezing and boiling points would have been noticeably different from 32 °F and 212 °F. Some time after his death, it was decided to recalibrate the scale with 32 °F and 212 °F as the exact freezing and boiling points of plain water. This resulted in the healthy human body temperature being 98.6 °F rather than 96 °F. That change was made to easily convert from Celsius to Fahrenheit and vice versa, with a simple formula. This change could also explain why the body temperature once taken as 100 °F by Fahrenheit is today taken by many as 98 °F—because that is a nice, round 37 °C—but more accurately yet in the neighborhood of 98°F. A fourth, not so well-known version of the origin of the Fahrenheit scale depends on Fahrenheit himself being a Freemason (of which there is no definitive evidence). In Freemasonry, there are 32 degrees of enlightenment, 32 being the highest. The use of the 'degree' as well is said to have been derived from the degrees of masonry. This may well be coincidence, but there is no conclusive evidence to the contrary, so the thought persists. In addition, a more humorous but very possible rumor regarding just how Fahrenheit chose his higher temperature involves a not-so-scientific approach to measuring the temperature of a human body. Supposedly, having no human volunteers from which to take his measurement, and not wanting to test it on himself (possibly for lack of an average between several bodies), he decided that the anal temperature of a common pig would closely match the internal body temperature of a human. He proceeded to mark the temperatures of several swine on a mercury tube, found the average, and claimed it to be correct. While the idea of a fairly esteemed scientist taking such a chance with measurement is questionable, given the fact that the body temperature of a pig is very close to that of a human, the logic behind this hasty decision would at least be fairly well placed. It is possible that, in a rush to meet a deadline determined by a boast or otherwise, it was his only option. This is, of course, only a rumor, though it could also account for the slight inaccuracy of Fahrenheit's 100 degree mark being the supposed internal body temperature of a human.

Usage

The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in most English-speaking countries until the 1960s. In the late 1960s and 1970s the Celsius (formerly centigrade) scale was phased-in by governments as part of the standardizing process of metrication. Fahrenheit supporters claim this is due to Fahrenheit's user-friendliness. The unit of measure, being only 5/9 the size of the Celsius degree, permits more precise communication of measurements without resorting to fractional degrees. Also, the ambient air temperature in most inhabited regions of the world tends not to go far beyond the range of 0 °F to 100 °F: therefore, the Fahrenheit scale would reflect the perceived ambient temperatures, following 10-degree bands that emerge in the Fahrenheit system:
- 10s Deep Frost.
- 20s Light Frost.
- 30s Cold. Close to freezing.
- 40s Cold. Heavy clothing needed.
- 50s Very cool. Moderate Clothing required.
- 60s Cool. Light clothing.
- 70s Comfortable. Summer clothing.
- 80s Warm. Bearable. Minimal clothing.
- 90s Hot.
- 100s Very hot. Take precautions against overheating. However, such a correlation is largely the result of habit: in the same way, Celsius supporters might indicate that 0–10 °C indicates cold, 10–20 °C mild, 20–30 °C warm and 30–40 °C hot, with the minus sign indicating frost. In the United States and Jamaica, where metrication has encountered greater resistance from industry and consumers, the Fahrenheit system continues to be very widely used for this purpose. In most parts of the United Kingdom Celsius has been adopted, although Fahrenheit is still occasionally used by older generations for everyday measurement of higher temperatures, while lower temperatures are more often measured in degrees Celsius. Younger generations in the UK and most other countries have adopted Celsius as the primary scale in use. In Canada, although the media is required to report temperatures in degrees Celsius, many older Canadians still describe temperatures in degrees Fahrenheit. In the United States of America Fahrenheit is popular in medicine too, it is well known that the normal body temperature in Fahrenheit is 98.6 degrees, and easy to remember that a temperature in excess of 100 degrees Fahrenheit requires medical attention. In the rest of the world, body temperature is measured in Celsius as being 37 °C.

Curiosities

The fire point, or kindling point, of paper is 451 °F (233 °C). This is why the title of the book by Ray Bradbury, an American, is Fahrenheit 451.

External links

- [http://www.straightdope.com/classics/a891215.html Alternate story at The Straight Dope] Category:Units of temperature Category:Imperial units Category:Customary units in the United States ko:화씨 ja:華氏

Kelvin scale

The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. It is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. A temperature given in kelvins, without further qualification, is measured with respect to absolute zero, where molecular motion stops. It is also common to give a temperature relative to the reference temperature of 273.15 K, approximately the melting point of water under ordinary conditions; this convention is the Celsius temperature scale. The kelvin is named after the British physicist and engineer William Thomson, 1st Baron Kelvin; his barony was in turn named after the River Kelvin, which runs through the grounds of the University of Glasgow.

SI multiples

Typographical conventions

The word kelvin as an SI unit is correctly written with a lowercase k (unless at the beginning of a sentence), and is never preceded by the words degree or degrees, or the symbol °, unlike degrees Fahrenheit, or degrees Celsius. This is because the latter are adjectives, whereas kelvin is a noun. It takes the normal plural form by adding an s in English: kelvins. When the kelvin was introduced in 1954 (10th General Conference on Weights and Measures (CGPM), Resolution 3, CR 79), it was the "degree Kelvin", and written °K; the "degree" was dropped in 1967 (13th CGPM, Resolution 3, CR 104). Note that the symbol for the kelvin unit is always a capital K and never italicised. There is a space between the number and the K, as with all other SI units. Unicode includes the "kelvin sign" at U+212A (in your browser it looks like K). However, the "kelvin sign" is canonically decomposed into U+004B, thereby seen as a (preexisting) encoding mistake, and it is better to use U+004B (K) directly.

Conversion factors

Kelvins and Celsius

The Celsius temperature scale is now defined in terms of the kelvin, with 0 °C corresponding to 273.15 kelvins.
- kelvins to degrees Celsius
- :

\mathrm = \mathrm - 273.15

Temperature and energy

In a thermodynamic system, the energy of the particles of a perfect gas is proportional to the absolute temperature, where the constant of proportionality is the Boltzmann constant. As a result, it is possible to determine the average kinetic energy

\overline

of the gas particles at the temperature T or to calculate the temperature of the gas from the average kinetic energy of the particles: :

\overline = \frac \cdot k_B \cdot \mathrm

External link

- [http://www1.bipm.org/en/si/si_brochure/chapter2/2-1/2-1-1/kelvin.html BIPM brochure on the kelvin] Category:SI base units Category:Units of temperature ko:켈빈 ja:ケルビン simple:Kelvin th:เคลวิน

Saffir-Simpson Hurricane Scale

:Category 1, Category 2 and Category 4 redirect here. For other meanings of Category 4, see Category 4 (disambiguation). The Saffir-Simpson Hurricane Scale is a scale classifying most Western Hemisphere tropical cyclones that exceed the levels of "tropical depression" and "tropical storm" and thereby become hurricanes. The "categories" it divides hurricanes into are distinguished by the intensities of their respective sustained winds. The classifications are intended primarily for use in gauging the likely damage and flooding a hurricane will cause upon landfall. The Saffir-Simpson Hurricane Scale is used only to describe hurricanes forming in the Atlantic Ocean and northern Pacific Ocean east of the International Date Line. Other areas label their tropical cyclones as "cyclones" and "typhoons", and use their own classification schemes.

History

It was developed in 1969 by civil engineer Herbert Saffir and Bob Simpson, at that time the director of the U.S. National Hurricane Center. The initial scale was developed by Saffir while on commission from the United Nations to study low-cost housing in hurricane-prone areas. While performing the study, Saffir realized there was no simple scale for describing the likely effects of a hurricane. Knowing the utility of the Richter magnitude scale in describing earthquakes, he devised a 1–5 scale based on wind speed that showed expected damage to structures. Saffir gave the scale to the NHC, and Simpson added in the effects of storm surge and flooding. It does not take into account rainfall or location, which means a Category 3 hurricane that hits a major city will likely do far more damage than a Category 5 hurricane that hits a rural area.

External links

- [http://www.nhc.noaa.gov/aboutsshs.shtml Descriptions of the likely damage and flooding caused by each category of hurricane] - The National Hurricane Center
- [http://www.novalynx.com/simpson-interview.html An Interview with Dr. Robert Simpson] - The Mariners Weather Log, April 1999
- [http://www.novalynx.com/saffir-interview.html Q&A with Herbert Saffir] - The South Florida Sun-Sentinel, June 2001 Category:Tropical cyclone meteorology Category:Scales ko:사피어-심프슨 허리케인 등급

Fujita scale

__NOTOC__ The Fujita scale, or Fujita-Pearson scale, rates a tornado's intensity by the damage it inflicts on human-built structures. Wind speed ranges were approximated to what was thought would cause the damage largely as educated guesses and have been found to be higher than the actual wind speeds required to incur the damage at each respective category (to an increasing degree as the category increases). It was introduced in 1971 by Tetsuya "Ted" Fujita of the University of Chicago who developed the scale together with Allen Pearson (path length and width additions in 1973), head of the National Severe Storms Forecast Center (predecessor to the Storm Prediction Center) in Kansas City, Missouri. Fujita scale ratings are issued after a tornado has passed through an area, not while it is on the ground. The official Fujita scale category is determined after meteorologists (and engineers) examine damage, ground-swirl patterns, radar tracking, eye-witness testimonies, media reports and damage imagery, and sometimes photogrammetry / videogrammetry. A tornado will be assigned the rating of the most severe damage to any well-built frame home or comparable level of damage from engineering analysis of other damage.

Fujita Scale Parameters

The seven categories are, in order of increasing intensity (F6 is not in use): (
- ) Relative frequency is of tornadoes in the United States. Frequencies of strong tornadoes are significantly less anywhere else in the world save Canada, Bangladesh and adjacent areas of eastern India. Also, due to many tornadoes never inflicting damage, the F0 numbers are somewhat inflated, compared to what damage some of the tornadoes are capable of producing.

External links

- [http://www.tornadoproject.com/fscale/fscale.htm The Fujita Scale of Tornado Intensity (Tornado Project)]
- [http://www.spc.noaa.gov/faq/tornado/f-scale.html Fujita Tornado Damage Scale (SPC/NOAA)]
- [http://www.ncdc.noaa.gov/oa/satellite/satelliteseye/educational/fujita.html The Fujita Tornado Scale (NCDC/NOAA)]
- [http://www.wind.ttu.edu/F_Scale/ Fujita Scale Enhancement Project (Wind Science and Engineering Research Center)] Category:Scales Category:Tornadoes

Scale factor (Universe)

The scale factor, parameter of Friedmann-Lemaître-Robertson-Walker model, is a function of time which represents the relative expansion of the universe. It relates physical coordinates (also called proper coordinates) to comoving coordinates. :

L = \lambda \; a(t)

where

L

is the physical distance,

\lambda

is the distance in comoving units, and

a(t)

is the scale factor. The scale factor could, in principle, have units of length or be dimensionless. Most commonly in modern usage, it is chosen to be dimensionless, with the current value equal to one:

a(t_0) = 1

, where t is counted from the birth of the universe and

t_0

is the present age of the universe: 13.7+/-0.2 Gyr. The evolution of the scale factor is a dynamical question, determined by the equations of general relativity, which are presented in the case of a locally isotropic, locally homogeneous universe by the Friedmann equations. The Hubble parameter is defined: :

H =

where the dot represents a time derivative. Category:Cosmology

Large-scale structure of the cosmos

Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. Currently, many large structures have been found; stars are organised into galaxies which in turn appear to form clusters and superclusters, separated by voids. Prior to 1989 it was commonly assumed that the superclusters were the largest structures in existence, and that they were distributed more or less uniformly throughout the universe in every direction. However, based on redshift survey data, in 1989 Margaret Geller and John Huchra discovered the "Great Wall", a sheet of galaxies more than 500 million light years long and 200 million wide, but only 15 million light years thick. The existence of this structure escaped notice for so long because it requires locating the position of galaxies in three dimensions, which involves combining location information about the galaxies with distance information from redshifts. redshift In more recent studies the universe appears as a collection of giant bubble-like voids separated by sheets and filaments of galaxies, with the superclusters appearing as occasional relatively dense nodes. At the centre of the local supercluster there is a gravitational anomaly, known as the Great Attractor, which is drawing in galaxies over a region hundreds of millions of light years across. These galaxies are all redshifted, in accordance with Hubble's law, as if they were receding from us and from each other, but the variations in their redshift are sufficient to reveal the existence of a concentration of mass equivalent to tens of thousands of galaxies. The Great Attractor, discovered in 1986, lies at a distance of between 150 million and 250 million light years (250 million is the most recent estimate), in the direction of the Hydra and Centaurus constellations. In its vicinity there is a preponderance of large old galaxies, many of which are colliding with their neighbours, and/or radiating large amounts of radio waves. Another indicator of large-scale structure is the 'Lyman alpha forest'. This is a collection of absorption lines which appear in the spectral lines of light from quasars, which are interpreted as indicating the existence of huge thin sheets of intergalactic (mostly hydrogen) gas. These sheets appear to be associated with the formation of new galaxies. Finally, there have been occasional claims of the quantisation of redshift. Although there have been numerous studies investigating this phenomenon, it is not widely regarded as valid, and remains the subject of considerable controversy. Some caution is required in describing structures on a cosmic scale because things are not always as they appear to be. Bending of light by gravitation (gravitational lensing) can result in images which appear to originate in a different direction from their real source. This is caused by foreground objects (such as galaxies) curving the space around themselves (as predicted by general relativity), deflecting light rays that pass nearby. Rather usefully, strong gravitational lensing can sometimes magnify distant galaxies, making them easier to detect. Weak lensing (gravitational shear) by the intervening universe in general also subtly changes the observed large-scale structure. As of 2004, measurements of this subtle shear show considerable promise as a test of cosmological models. The large-scale structure of the Universe also looks different if one only uses redshift to measure distances to galaxies. For example, galaxies behind a galaxy cluster will be attracted to it, and so fall towards it, and so be slightly blueshifted (compared to how they would be if there were no cluster); on the near side, things are slightly redshifted. Thus, the environment of the cluster looks a bit squashed, if using redshifts to measure distance. An opposite effect works on the galaxies already within the cluster: the galaxies have some random motion around the cluster centre, and when these random motions are converted to redshifts, the cluster will appear elongated. This creates what is known as a finger of God: the illusion of a long chain of galaxies pointed at the Earth. There is much work in cosmology which attempts to model the large-scale structure of the universe. Using the big bang model and assumptions about the type of matter that makes up the universe, it is possible to predict the expected distribution of matter, and by comparison with observation work backward to support and refute certain cosmological theories. Currently, observations indicate that most of the universe must consist of cold dark matter. Models which assume hot dark matter or baryonic dark matter do not provide a good fit with observations. The irregularities in the cosmic microwave background radiation and high redshift supernovae give complementary approaches to constraining the same models, and there is a growing consensus that these approaches together are giving evidence that we live in an accelerating universe. In the quasi-steady state model of Hoyle, Burbidge and Narlikar, the process of structure formation has been studied in the context of a "toy model" which may be a viable alternative to the standard hot big bang model of structure formation. ja:宇宙の大規模構造

Palermo Technical Impact Hazard Scale

The Palermo Technical Impact Hazard Scale is a logarithmic scale used by astronomers to rate the potential hazard of impact of a near-earth object. It combines two types of data—probability of impact, and estimated kinetic yield—into a single "hazard" value. A rating of 0 means the hazard is as likely as the background hazard (defined as the average risk posed by objects of the same size or larger over the years until the date of the potential impact). A rating of +2 would indicate the hazard is 100 times more likely than a random background event. A similar but less complex scale is the Torino scale, which is used for simpler descriptions in the non-scientific media. The Palermo Scale value, P, is defined as the base 10 logarithm of the ratio of the impact probability p_i to the background impact probability over the time T to the event: :

P = \log_ \frac

The annual background impact frequency is defined for this purpose as: :

f_B = 0.03 E^ \;

where the energy threshold E is measured in megatons. The near-Earth object was the first near-Earth object detected by NASA's latest NEO programme to be given a positive rating on the scale of 0.06, indicating a higher than background threat. The value was subsequently lowered to −0.25 after more measurements were taken. On December 27, 2004, asteroid 99942 Apophis (then known only by its provisional designation ) briefly held the record for Palermo scale values, with a value of 1.10 for a possible collision in the year 2029. The 1.10 value indicated that a collision with this object was considered to be almost 12.6 times more likely than a random background event: 1 in 37 instead of 1 in 472. With further observations, the possibility of a 2029 impact was eliminated, but as of 2005 a cumulative Palermo rating of about −1.3 applies, largely due to possible events in 2035 and 2036. Before Apophis, asteroid (29075) 1950 DA held the record for Palermo scale values, with a value of 0.17 for a possible collision in the year 2880.

External links

- NASA NEO Programme http://neo.jpl.nasa.gov/index.html
- Description of the scale http://neo.jpl.nasa.gov/risk/doc/palermo.html
- (89959) 2002 NT₇ is the [http://news.bbc.co.uk/2/hi/science/nature/2147879.stm first object discovered with a positive measurement on the Palermo scale] Category:Scales

Mulliken scale

The Mulliken scale (also called Mulliken-Jaffe scale) is a scale for the electronegativity of chemical elements. It was developed by Robert S. Mulliken in 1934. It is based on the Mulliken electronegativity, c_M, which is related to the electron affinity EA_v (the tendency of an atom to become negatively charged) and the ionization potential IE_v (the tendency of an atom to become positively charged): :c_M = (IE_v + EA_v)/2 Some example values:

Element	Al<