b'\x1b\x1a\x19 \x1f\x18\x1d\x17\x16Metric MattersJOULE, WATT AND COULOMBBy Edmund IsakovO nOct.21,1948,theninthThis is thefth in a series of articles about the metric system.meeting of the General Con-ference on Weights and Measures, also known as CGPM, adopted theConversion of units of energy, work or amount of heat from the metric system to the joule as a unit of energy, work andU.S. customary system and vice versaamount of heat from the force of a newton acting to move an object1 J = 0.73756 ft-lbf 1 ft-lbf = 1.35582 Jthrough a distance of 1 m in the di- 1 J = 0.23892 cal(15 C) 1 cal= 4.1855 Jrection in which the force is applied. 15 15Mathematical expression of the joule is: J = Nm = (kgms 2 )mmetric unit of energy. Calis thepower rate of 1 J of work per sec-15= kgm 2 s 2 . Expression of the jouleamount of energy needed to warmond. In the latter, a watt is the power in terms of SI base units is: m 2 kg 1 g of water from 14.5 C to 15.5 Cproduced by the current of an am-s -2 . Expression of the joule in terms ofat the standard atmospheric pres- pere flowing through the electric SI-derived and base units is: Nm. sure of 760 mm of mercury. potential of a volt.James Prescott Joule (1818-1889)On Oct. 21, 1948, the ninth CGPMMathematical expression of the was an English physicist. His ex- adopted the watt as a unit of power.watt is: W = Js = (Nm)s = [(kgperiments and measurements al- Power is the rate at which work isms 2 m)]s = kgm 2 s 3 . Expres-lowed him to estimate the mechani- done or the rate at which energy ission of the watt in terms of SI base cal equivalent of heat. The joule isexpended. This unit is used in bothunits is: m 2 kgs -3 . Expression named after him. mechanical and electrical terms.of the watt in terms of SI-derived Note that the calorie is a pre-SIIn the former, a watt is equal to aand base units is: Js -1 ; NmJoule Watt CoulombUnit: joule Unit: watt Unit: coulombMeasure: energy, work, amount of heat Measure: power Measure: electric charge, amount of electricitySymbol: J Symbol: W Symbol: C18SEPTEMBER 2020MetricMatters.indd 18 8/14/20 4:13 PM'