Mechanics of engineeringComprising statics and dynamics of solids: and the mechanics of the materials of constructions, or strength and elasticity of beams, columns, arches, shafts, etc . affecting the principle ofwork and energy in machines,take the simple case in Fig. helical spring at a given in-stant is acted on at each end bya force P in an axial direction(they are equal, supposing the Fig. 160. mass of the spring small). As the machine operates of whichit is a member, it moves to a new consecutive position B,suffering a further elongation dX in its length (if P is increas-ing). P o
Mechanics of engineeringComprising statics and dynamics of solids: and the mechanics of the materials of constructions, or strength and elasticity of beams, columns, arches, shafts, etc . affecting the principle ofwork and energy in machines,take the simple case in Fig. helical spring at a given in-stant is acted on at each end bya force P in an axial direction(they are equal, supposing the Fig. 160. mass of the spring small). As the machine operates of whichit is a member, it moves to a new consecutive position B,suffering a further elongation dX in its length (if P is increas-ing). P on the right, a working force, does the work Pdx;how is this expended 1 P on the left has the work Pdx doneupon it, and the mass is too small to absorb kinetic energy orto bring its weight into consideration. The remainder, Pdx— Pdx = PdX, is expended in stretching the spring an addi-tional amount dX, and is capable of restoration if the springretains its elasticity. Hence the work done in changing theform of bodies if they are elastic is said to be stored in theform of potential energy. That is, in the operation of ma-chines, the name potential energy is also given to the energy. 156 MECHANICS OF ENGINEERING. stored and restored periodically in the changing and regainingof form of elastic bodies. 149. Other Forms of Energy.—Numerous experiments with?various kinds of apparatus have proved that for eveiy 772(about) of work spent in overcoming friction, one Britishunit of heat is produced (viz., the quantity of heat necessary toraise the temperature of one pound of wTater from 32° to 33°Fahrenheit); while from converse experiments, in which theamount of heat used in operating a steam-engine was all carefullyestimated, the disappearance of a certain portion of it could onlybe accounted for by assuming that it had been converted intowork at the same rate of (about) 772 of work to eachunit of heat (or 425 kilogrammetres to each French unit ofheat). This number
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectenginee, bookyear1888
