AGE OF MACHINERY 



499 



Work, Whenever a person exerts force through any distance, 

 such as shoveling coal, lifting a stove cover, raising a window, walk- 

 ing upstairs, etc., work is accomplished. Work is measured in foot 

 pounds. A foot pound of work is accomplished when a pound is 

 raised a distance of one foot. A horse power is equal to 550 foot 

 pounds in one second. 



Friction and Mechanical Advantage. A great deal of work is 

 done to overcome friction. For that reason perpetual motion 



FIG. 381. Automobile transmission. 

 Find as many mechanical advan- 

 tages as possible. Tell why they 

 are mechanical advantages. 



FIG. 382. Dish-washing ma- 

 chine. 



machines can not exist, for more work always has to be put into 

 a machine than is actually obtained from the machine. Machines 

 do not save work, but permit a smaller force to be applied for a 

 longer time. 



Machines are used by men to gain some advantage, and this 

 advantage is called the mechanical advantage of the machine. Many 

 things may be moved with a crowbar which could not otherwise 

 be moved, A hammer will draw a nail which could not be drawn 



