All About Engines

How a Modern Engine Works 19 of work. The next step is more easily put into a table : 2 lb. lifted through 1 ft. =2 ft-lb. 1 „ 2 ft = 2 ft.-lb. 3 lb. „ „ i ft. = 3 ft.-lb. 1 lb- » n 3 ft. = 3 ft.-lb. and so on, so that 10 lb. lifted through 25 feet repre- sents 250 ft.-lb. of work, and generally the work done in lifting x lb. through a vertical height of y feet is x x y ft.-lb. This statement is not only true in reference to lifting weights, but in all cases where a force applied to a body succeeds in moving it or deforming it—that is, altering its shape. Thus if a force of 10 lb. applied to a heavy table is sufficient to move it steadily across the room without leaving the floor, then 15 ft.-lb. of work will have been done when it has moved ij feet, 30 ft.-lb. when it has moved 3 feet, 70 ft.-lb. when it has moved 7 ft., and so on. Again, if a quantity of gas is enclosed in a long, uniform tube by a piston, and if the piston is forced slowly inwards so that the length occu- pied by the gas is half the original length, then the average force employed multiplied by the distance through which the piston has moved will give the work done in compressing the gas. Suppose, as another example, a force is applied to the handle of a grindstone, or the mangle used in the laundry. If the arm to which the handle is attached is 1 foot long and the force necessary to keep the grindstone or mangle moving steadily is