24 APPLIED SCIENCE 



The unit of work is the product of the unit of weight and the 

 unit of distance. When one pound is raised one foot (against 

 the force of gravity) it is called a foot-pound. 



Therefore the weight in pounds multiplied by the distance in 

 feet gives the number of foot-pounds. By this means the energy 

 expended in lifting a weight is measured. 



Pounds X Feet = Foot-Pounds 

 1 Ib. X 1 ft. = 1 ft.-lb. (one unit of work) 



When 847 Ibs. is raised 12 ft., the work done is 847x12 = 

 10,164 ft.-lbs. 



Power is the rate of doing work, or work done in unit time. 

 In other -words, power is the number of foot-pounds of work 

 that can be done per minute or per second. 



To illustrate: If a man exerts a force of 80 Ibs. in pushing a wagon 

 60 ft. in one minute, the rate of doing work during that minute is 

 80 X 60 = 4800 ft.-lbs. If the same amount of work is performed 



4800 

 in two minutes, then the rate of doing work is - = 2400 ft.-lbs. 



per minute. The unit of power is the horse-power (H. P.) 33,000 

 ft.-lbs. per minute, or 550 ft.-lbs. per second. Watt, years ago, 

 found this to be the rate at which an average horse can work, hence 

 the name. 



Energy is the ability to do work, and is classified according 

 to its source animal energy, mechanical energy, electrical 

 energy, etc. 



26. Mechanical Principles. A tool or machine is com- 

 posed of one or more of the following mechanical elements.: 

 a lever, wheel and axle, pulley, inclined plane, wedge and 



