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mass

mass  

A measure of a body's inertia, i.e. its resistance to acceleration. According to Newton's laws of motion, if two unequal masses, m1 and m2, are allowed to collide, in the absence of any other forces ...
radon

radon   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
113 words

...to group 18 of the periodic table (the noble gases); a.n. 86; r.a.m. 222; d. 9.73 g dm −3 ; m.p. −71°C; b.p. −61.8°C. At least 20 isotopes are known, the most stable being radon–222 (half-life 3.8 days). It is formed by decay of radium–226 and undergoes alpha decay. It is used in radiotherapy. Radon occurs naturally, particularly in areas underlain by granite, where it is thought to be a health hazard. As a noble gas, radon is practically inert, although a few compounds, e.g. radon fluoride, can be made. It was first isolated by William Ramsey and Robert...

americium

americium   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
59 words

...americium Symbol Am. A radioactive metallic transuranic element belonging to the actinoids; a.n. 95; mass number of most stable isotope 243 (half-life 7.95 × 10 3 years); r.d. 13.67 (20°C); m.p. 994 ± 4°C; b.p. 2607°C. Ten isotopes are known. The element was discovered by G. T. Seaborg and associates in 1945 , who obtained it by bombarding uranium–238 with alpha...

deuterium

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A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
102 words

...or fractional distillation. Its chemical behaviour is almost identical to hydrogen although deuterium compounds tend to react rather more slowly than the corresponding hydrogen compounds. Its physical properties are slightly different from those of hydrogen, e.g. b.p. 23.6 K (hydrogen 20.4...

mass

mass   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
547 words

...it produces. Thus, according to Newton’s law of gravitation, m g = Fd 2 / MG , where M is the mass of a standard body situated a distance d from the body of mass m g ; F is the gravitational force between them and G is the gravitational constant . The mass defined in this way is the gravitational mass . In the 19th century Lóránd Eötvös ( 1848–1919 ) showed experimentally that gravitational and inertial mass are indistinguishable, i.e. m i = m g . Experiments performed in the 20th century have confirmed this conclusion to even greater...

radiography

radiography   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
864 words
Illustration(s):
1

...of the attenuation with the atomic number (Z) of the medium substance Energy range in which this kind of attenuation is dominant simple scattering ∝ 1/ E ∝ Z 2 1–20keV photoelectric effect ∝ 1/ E 3 ∝ Z 3 1–30keV Compton scattering falls gradually with E independent 30keV–20MeV pair production rises slowly with E ∝ Z 2 above 20 MeV Air has a higher average Z than soft tissue, which consists of mostly carbon ( 6 C) and hydrogen ( 1 H). However, the low average density of air means that it does not attenuate...

quantum mechanics

quantum mechanics   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
1,612 words
Illustration(s):
3

...based on quantum theory , which arose out of the failure of classical mechanics and electromagnetic theory to provide a consistent explanation of both electromagnetic waves and atomic structure. Many phenomena at the atomic level puzzled physicists at the beginning of the 20th century because there seemed to be no way of explaining them without making use of incompatible concepts. One such phenomenon was the emission of electrons from the surface of a metal illuminated by light. Einstein realized that the classical description of light as a wave on...

mega-

mega-   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...[Gk: ‘great’] Symbol M-. Metric The 10 6 multiplier, e.g. 1 megajoule = 1 MJ = 10 6 J; contractable to meg- before a vowel, e.g. 1 megohm = 1 MΩ = 10 6 Ω. informatics . Sometimes 1 048 576 = 2 20 , but see mebi- then kibi-...

poise

poise   Quick reference

A Dictionary of Weights, Measures, and Units

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Subject Reference
Current Version:
2004

...[ J. L. M. Poiseuille ; France 1799–1869 ] dynamic viscosity . Symbol P. Metric-c.g.s. Identically dyne⋅second per square centimetre (dyn⋅s⋅cm -2 ) = 10 -1 N⋅s⋅m -2 = 10 -1 Pa⋅s(= cm -1 ⋅g⋅s -1 in c.g.s. base terms). Hence • P⋅(g⋅cm -3 ) -1 = stokes for kinematic viscosity. The poise is a large unit for most purposes, water at 20°C having a viscosity of 10.020∼ mP and most free-flowing liquids typically being similar; gases are around 1 μP. There is no equivalent special term in the...

gallon

gallon   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...L (0.832 674 2∼ BI gal). See Table 17(b). US-C dry There is no gallon for dry goods; see bushel . Table 17(a) BI, Australia, Canada, New Zealand, etc., SI US-C liq fl oz … … … … … 28.4∼ mL 0.961∼ oz 5 gill … … … … 142∼ mL 4.80∼ oz 20 4 pint … … … 568∼ mL 1.20∼ pt 40 8 2 quart … … 1.14∼ L 1.20∼ qt 160 32 8 4 gallon … 4.55∼ L 1.20∼ gal 2 peck 9.09∼ L 2.40∼ gal 8 4 bushel 36.4∼ L 9.61∼ gal For downward extension, see fluid ounce . Table 17(b) US-C for liquids SI liq oz … … … … … 29.6∼ mL 4 gill … … … … 118.∼ mL 16 4 pint … … … 473.∼ mL 32 8 2 quart … … 946.∼...

apothecaries' scale

apothecaries' scale   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...the UK, e.g. oz ap. Unlike the more usual avoirdupois scale with its pound of 16 ounces and 7 000 grains (making its ounce 437.5 gr), the apothecaries' scale, like the troy scale , has a pound of only 12 ounces each of 480 grains, giving a total of 5 760 grains, the grain being the one unit common to all three scales. The distinctive scale for apothecaries' units is shown in Table 2. Table 2 BI-apoth, US-C-ap Internat values: SI US-C-av grain … … … 64.8∼ μg 1 gr 20 scruple … … 1.30∼ g 20 gr 60 3 drachm, dram … 3.89∼ g 60 gr 480 24 8 ounce 31.1∼ g 1.10∼ oz...

poiseuille

poiseuille   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...metre or kilogram per metre⋅second, = N⋅s⋅m -2 = Pa⋅s; there is no use of it else any equivalent term in the SI (= m -1 ⋅kg⋅s -1 in m.k.s. base terms). It has rarely been used outside of France. Even more than its predecessor, the poise of c.g.s., the poiseuille is a large unit for most purposes, water at 20°C having a viscosity of 1.002 0∼ mPl and most free-flowing liquids typically being similar, with gases being below 1...

windchill (factor)

windchill (factor)   Quick reference

A Dictionary of Weights, Measures, and Units

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Subject Reference
Current Version:
2004

...to reflect the greater freezing effect, particularly on hairless human skin and flesh, of low temperatures when accompanied by significant wind. The initial form consisted merely of subtracting the Fahrenheit temperature from the wind speed measured in miles per hour, e.g. a wind of 20 m.p.h. and a temperature of -30°F gave a windchill of 50, equatable with -50°F in calm conditions. The real effect is far from linearly additive in such a simple (and convenient) manner. Careful study has produced more complex formulations, convertible to a rate of heat loss...

pound

pound   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...g, so 1 kg = 2.204 622 62∼ lb. Bigg P. H. Nature 194, 719–21 (1962) Canada 1951 453.592 43 g, so 1 kg = 2.204 622 33∼ lb.Canada: An Act respecting Weights and Measures assented to 20 June 1951 BI 1898 By Order-in-Council it was declared that, on the basis of comparative measurement of the prototype pound and the international prototype kilogram, 1 kg = 2.204 622 3 lb, so 1 lb = 453.592 436∼ g (making the prototype pound obsolescent, but not displacing it). US-C 1893 Defined by the Mendenhall Order , = 1 / 2.20462234 kg = 1 / 453.5924277 ∼ g,...

binary

binary   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...Relating to anything having just two alternatives, or based on such (see below), in contrast with the steps of 10 and its powers for decimal and its compounds, of 12 for duodecimal , 16 for hexadecimal , 20 for vigesimal , 60 for sexagesimal , etc. In both the material and the electrical worlds, from the presence or absence of an item (e.g. a hole in a card, the on/off of electricity) to the north/south polarity of magnetism, the binary state is of widespread natural significance. Hence, although efforts to mimic decimal notation have been made, the...

preferred numbers

preferred numbers   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...R10″, precise sub-sets of the denser set for the same level of rounding, specifically every second and every fourth, starting at 10. Any such methodical subset can be used, e.g. R20′/3 (10‥40) for every third value of R20′ running from 10 to 40, i.e. the values 10, 14, 20, 28, 40. The USA has an equivalent standard used worldwide for electronic components, but with the number of steps binary multiples of 6 rather than of 5, ranging up to 192 steps. (It has also had a standard using fractions of an inch. Van Dyck A. Proc. Inst. Radio Engrs 24, 159–79...

hundredweight

hundredweight   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...hundredweight ) in North America. See pound for more precise values, and Table 25 for scales. Table 25(a) BI, Australia, New Zealand SI lb … … … … 454.∼ g 14 stone … … … 6.35∼ kg 28 2 quarter … … 12.7∼ kg 112 8 4 hundredweight … 50.8∼ kg 2 240 20 ton 1016.∼ kg For downward extension, see ounce . Table 25(b) US-C, Canada SI lb … … … … 454.∼ g 25 quarter … … 11.3∼ kg 100 4 hundredweight … 45.4∼ kg 2 000 20 ton 907.∼ kg For downward extension, see ounce . The cwt was removed from official UK measures in 1985 .The UK Weights and Measures Act 1985 ...

calorie

calorie   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

...for any precise use, since the amount is dependent on starting temperature. This is denoted by a suffix, e.g. cal 15 denotes the rise from 14.5 to 15.5°C; cal mean denotes the mean per degree over the range 0 to 100°C. international steam calorie cal IT = 4.186 74∼ J, mean calorie cal mean = 4.190 02∼ J 4°C calorie cal 4 = 4.204 5∼ J (water at its densest) 15°C calorie cal 15 = 4.185 5∼ J (15°C = cool indoors) 20°C calorie cal 20 = 4.181 90∼ J (20°C = warm indoors) The cal 15 is usually meant by the mechanical equivalent of heat . The international steam...

normalized

normalized   Quick reference

A Dictionary of Weights, Measures, and Units

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Current Version:
2004

...mathematics . Applied to numbers expressed as a mantissa multiplied by an exponential expression, e.g. 8.97∼ × 10 20 , the term applies to having the mantissa within some defined range. The above is identically 0.897∼ × 10 21 , 89.7∼ × 10 19 , 897.∼ × 10 18 , 0.089 7∼ × 10 22 , and any other of the unlimited equivalent variants. Clearly any non-zero number can be written such that the mantissa is within some pre-set range that spans, multiplicatively, the size of the base. For base 10, as in the above example, we can fix the range to be from 1...

pitch

pitch   Quick reference

A Dictionary of Weights, Measures, and Units

Reference type:
Subject Reference
Current Version:
2004

... f 293.665∼ D 1.189 2∼ f 311.127∼ • (5 f /4 = 1.250 0 f ) 1.259 9∼ f 329.628∼ E (4 f /3 = 1.333 3∼ f ) 1.334 8∼ f 349.228∼ F 1.414 2∼ f 369.994∼ • (3 f /2 = 1.500 0 f ) 1.498 3∼ f 391.995∼ G 1.587 4∼ f 415.305∼ • (5 f /3 = 1.666 7∼ f ) 1.661 8∼ f 440. A 1.781 8∼ f 446.164∼ • (15 f /8 = 1.875 0 f ) 1.887 7∼ f 493.883∼ B (2 f /1 = 2 f ) 2.0 f 523.251∼...

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