314 AGRICULTURAL ENGINEERING 



in the form of food, fuel, or wind and convert it into mechan- 

 ical energy, which may be used in driving machinery. The 

 electric motor is driven by electric energy, furnished either 

 by an electric generator, driven by a prime mover, or by 

 chemical action, like the electricity from an electric battery. 

 Forces. A force is that which produces, or tends to pro- 

 duce or destroy, motion. A force has two 

 characteristics, magnitude or size, and direc- 

 tion. The unit by which the magnitude 

 FtrceA of a force is designated or measured is the 



Fig. 195. pound. The pound is the action of the force 

 of gravity on a definite mass. When two or 

 more forces act at a point their combined 

 action is equal to the action of one force, 

 called the resultant. In a reverse manner a 

 force may be divided into components, which act in different 

 directions from that of the force. 



Work. When a force acts through a certain distance, or 

 when motion is produced by the action of a force, work is 

 done. Work is often defined as the product of force times 

 distance. 



The Unit of Work. The unit of work is the foot pound, 

 or the equivalent of the force of one pound acting through a 

 distance of one foot. Thus, for example, the work done in 

 raising a weight of one pound five feet or five pounds one foot 

 would be five foot pounds. 



Power. Power is the rate of work. In determining the 

 rate of work time is a factor. Thus the measurement of 

 power consists in determining the number of foot pounds of 

 work done in a certain time. 



The Unit of Power. The unit of power in common use is 

 the horsepower. It was established arbitrarily, and is 

 equal to 33,000 foot pounds of work per minute. Thus if the 



