A text book of elementary mechanics, for the use of colleges and schools . which could be revolvedby means of a string passing over two pulleys C and D,and attached to two known weights E and F. If now * The experiments of Dr. Joule were carried on between 1843and 1849. He employed several different methods for determin-ing the mechanical equivalent of heat, but that which led tothe most satisfactory results is the one here described. i 111.] MECHANICAL ENERGY AND HEAT. 117 these weights (E + F = W) are allowed to descendfreely through a distance //, marked on the verticalscales, the work done
A text book of elementary mechanics, for the use of colleges and schools . which could be revolvedby means of a string passing over two pulleys C and D,and attached to two known weights E and F. If now * The experiments of Dr. Joule were carried on between 1843and 1849. He employed several different methods for determin-ing the mechanical equivalent of heat, but that which led tothe most satisfactory results is the one here described. i 111.] MECHANICAL ENERGY AND HEAT. 117 these weights (E + F = W) are allowed to descendfreely through a distance //, marked on the verticalscales, the work done is Wk; but this is expended inturning the paddle in the water, and, owing to the fric-tion of the water (Art. 87), is all transformed into if the amount of water is known, and its tempera-ture before and after the experiment, the number offoot-pounds of work required to produce one heat-unit—that is, to raise 1 lb. of water 1° C.—can be readilycalculated. In the actual experiment it was necessaryto make corrections for the loss of energy in the friction. Fig. 44. Fig. 45. of the pulleys, the radiation of heat from the box, andseveral other points which need not be explained result obtained was this: That an expenditure of1390 foot-pounds of work produce one unit of heat on theCentigrade scale (772 on the Fahrenheit scale).Many other experiments have been made in various wayshaving as their object jbhe determination of this samerelation; for example, the amount of heat produced bythe friction of two iron plates in mercury, that causedby the collision of two heavy bodies one of which has 118 DYNAMICS. fallen through a known height, and so on. All theseexperiments have confirmed the relation obtained byJoule. 112. Conversion of Heat into Work. Since a definiteamount of mechanical work is equivalent to a certainamount of heat energy, the converse must also be true:that heat is convertible into mechanical Avork. Thisconversion of the former kind of
Size: 2263px × 1104px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, booksubjectmechanics, bookyear18
