36 FORCE AND THE LAWS OF MOTION 



law as applied to particles we shall be able to deduce laws which 

 shall apply to bodies of finite size. This problem will be treated 

 in a later chapter. Although, however, in strictness, the laws 

 ought to be applied only to particles, it is obvious that there may 

 be many problems in which we can treat bodies of finite size as 

 particles without introducing any appreciable error. Such a case 

 occurred when we discussed the flight of the bullet in 18 : the 

 size of the bullet did not come into the question, as we could 

 imagine all the points of the bullet to have the same acceleration. 

 Many cases will occur in which a body of finite size may be treated 

 as though it were a particle. In the next chapter we shall con- 

 sider the application of forces to particles and to bodies which we 

 find it is permissible to treat as particles. 



