IO FARM MACHINERY 



Farm Motors. The following definitions and explana- 

 tions will prove helpful : 



15. A force produces or tends to produce or destroy 

 motion. Forces vary in magnitude, and some means must 

 be provided to compare them. Unit force corresponds to 

 unit weight and is the force of gravitation on a definite 

 mass. This unit is arbitrarily chosen and is called the 

 pound. The magnitude of all forces, as the draft of an 

 implement, is measured in pounds. Forces also have 

 direction and hence may be represented graphically by a 

 line. For this reason a force is sometimes called a vector 

 quantity. Two or more forces acting on a rigid body act 

 as one force called a resultant. 



Thus in Fig. I, O A and O B rep- 

 resent in direction and magnitude 

 x \ two forces acting through the point 

 y'* O. O C is the diagonal of a paral- 

 lelogram of which O A and O B are 

 A' sides, and represents the combined 



action of the forces represented by 



O A and O B, or is the resultant of these forces. This 

 principle is known as the parallelogram of forces. 



16. Mechanics is the science which treats of the action 

 of forces upon bodies and the effect which they produce. 

 It treats of the laws which govern the movement and 

 equilibrium of bodies and shows how they may be util- 

 ized. 



17. Work. When a force acts through a certain dis- 

 tance or when motion is produced by the action of a 

 force, work is done. Work can therefore be defined as 

 the product of force into distance. Work can be defined 

 in another way as being proportional to the distance 

 through which the force acts, and also to the magnitude 

 of the force. 



