All About Engines

3°& All About Engines 25 = 250 ft.-lb. of work. The work done in lifting is al- ways equal to the product of the weight lifted in pounds, and the height through which it is raised in feet. This is true not only of lifting, but in all cases where a force applied to a body succeeds in moving it. If a force of 10 lb. applied to heavy table is suffi- cient to move it steadily across a room, then 15 ft.-lb. of work will be done when it has moved feet. 30 ft.-lb. when it has moved 3 feet, 70 ft.-lb. when moved 7 ft., and so on. Again, if a force is applied to the handle of a grind- stone the same rule will apply. Suppose the arm on which the handle is fixed is 1 foot long, and the weight required to keep the grindstone moving steadily is 7 lb., then, since the diameter of the circle round which the force moves is 2 feet, the distance which the force moves in one revolution is 2 x 31 == 2 x 22 = 44 feet, 7 7 7 and the work done in one revolution is 7 lb. x 4Æft. = 44 ft.-lb. For twenty revolutions 44 x 20 = 880 ft.-lb. will be required. It will be evident that work can be stored up in a body which is lifted or set in motion. If a weight of 14 lb. is lifted 5 feet it will have 70 ft.-lb. stored up in it by reason of its position. And if in falling back to its lower position it drags a rope after it this rope may be made to lift another weight. But it would not lift 14 lb. through 5 feet because the pulley