Machinery's Handbook, 31st Edition
US Customary Unit System 2835 The Treaty of the Meter was signed in 1875, and the International Bureau of Weights and Measures (BIPM) in Severs, France, created 30 prototype line standards of platinum iridium. In 1889, United States received Nos. 27 and 21 prototype meters from BIPM. No. 27 was used as a standard for the U.S. metric system from 1889 to 1960, but then a new standard was adopted, based not on an object whose dimensions could change over time but on a physical constant related the number of wavelengths krypton-86 emits during a specific energy level transition. In 1983 the meter was again redefined, described now in terms of the speed of light. In 2019, the standard was once more updated, based on an even more precise measurement of the speed of light. Prototype meter No. 27 is now kept in the NIST museum. According to U.S. 1988 Law on Metrification, the country would phase out the imperial and US customary unit, replacing them with their metric equivalents. As of 2018, the use of the metric system in trade and commerce was mandatory in all countries except the United States, Myanmar, and Liberia. The meter has gone through several restandardizations. In 1983, the modern base unit was set as that length equal to the path length traveled by light in a vacuum during a time interval of 3.3356410 × 10 –9 second. The new meter represents the most advanced ideas of physical measurement, much like the second is based on the Cs 133 atomic clock. Each new meter represented the most advanced ideas of standards, so it seemed that greater stability, as well as higher accuracy, would be secured by accepting the international meter as a fundamental standard of length. The director of national standard laboratory of the United States entered into agreement effective July 1, 1959, whereby the equivalent of 1 yard = 0.9144 meter and 1 avoirdupois pound = 0.45359237 kilogram, where adapted. In the United States, the SI metric system of units is predominantly used in the fields of physics, chemistry, and other sciences; however, U.S. customary units are still widely used in industry and by the general public. Fundamental Constants Name Symbol USCS units SI units Avogadro’s number N A 6.022 3 10 23 mol − 1 Boltzman constant k 5.65 3 10 − 24 ft · lb f / ° R 1.38065 3 10 − 23 J/K Faraday Constant F 96,485 C/mol Gravitational constant g 32.174 lb m -ft/lb f -sec 2 9.80667 m/sec 2 Gravitational constant G 5.65 3 10 − 24 ft · lb f / ° R 6.672 3 10 − 11 N · m 2 /kg 2 Specific gas constant R 53.3 ft · lb f /lb m · ° R 287 J/kg · K Universal gas constant R 1545 ft · lb f /lbmol · ° R 8314 J/kmol · K Volume (molal ideal gas) V 359 ft 3 /lbmol 22.41 m 3 /kmol Pressure, atmospheric P 14.696 lb f /in 2 101,330 Pa (N/m 2 ) Temperature, standard T 32 ° F 0 ° C Density Air at 32 ° F (0 ° C) 0.0805 lb m /ft 3 1.29 kg/m 3 Air at 70 ° F (20 ° C), 1 atm 0.0749 lb m /ft 3 1.20 kg/m 3 Sea water 64 lb m /ft 3 1025 kg/m 3 Fresh water 62.4 lb m /ft 3 1000 kg/m 3 Mercury 849 lb m /ft 3 13600 kg/m 3 Earth 345 lb m /ft 3 5520 kg/m 3
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