. Practical physics. weights in causing them to descendthrough any distance (/ was equalto their weight W tinies this dis-tance. If the weights descendedslowly and uniformly, this workwas all expended in overcomingthe resistance of the water tothe motion of the paddle wheelsthrough it; that is, it was wastedin eddy currents in the measured the rise in thetemperature of the water andfound that the mean of his threebest trials gave 427 gram metersas the amount of work required to d-evelop enough heat to raise a gram of water one degree. This value,confirmed by modern experiments, is
. Practical physics. weights in causing them to descendthrough any distance (/ was equalto their weight W tinies this dis-tance. If the weights descendedslowly and uniformly, this workwas all expended in overcomingthe resistance of the water tothe motion of the paddle wheelsthrough it; that is, it was wastedin eddy currents in the measured the rise in thetemperature of the water andfound that the mean of his threebest trials gave 427 gram metersas the amount of work required to d-evelop enough heat to raise a gram of water one degree. This value,confirmed by modern experiments, is now generally accepted as then repeated the experiment, substituting mercury for water, andobtained gram meters as the work necessary to produce a calorie ofheat. The difference between these numbers is less than was to havebeen expected from the unavoidable errors in the observations. Hethen devised an arrangement in which the heat was developed by thefriction of iron on iron, and again obtained Fig. 108. Joules first experiment onthe mechanical eqvuvalent of heat 154 WORK AJsD HEAT ENERGY 184. Heat produced by collision. A Frenchman namedHirn was the first to make a careful cletermmation of therelation between the heat developed by collision and the kineticenergy which disappears. lie allowed a steel cylinder to fallthrough a known height and crush a lead ball by its impactupon it. The amount of heat developed in the lead was meas-ured by observing the rise in temperature of a small amount ofwater into which the lead was quickly plunged. As the meanof a large number of trials he also found that 425 gram metersof energy disappeared for each calorie of heat that appeared. 185. Heat produced by the compression of a gas. Another wayin which Joule measured the relation between heat and workwas by compressing a gas and comparing the amount of workdone in the compression with the amount of heat developed. Every bicyclist is aware of the fact tliat when he infla
Size: 1844px × 1356px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectphysics, bookyear1922
