If you put a ball on the ground, it will stay there. It does not move by itself. It will move only when you kick it. If you kick it hard, it moves faster. To move a heavy stone across a room lot of pushing has to be done. But to move a sheet of paper off your table requires a very little push. Can you think of a situation when a cart is moving without bullocks?Perhaps not (Fig. 8.1). It means something has to be done to move a body from rest or to make it move slow or fast.
You can also stop a moving ball by catching it or putting an obstacle in its path. It means something is done to stop a moving body.
Consider another example in which the volleyball players are hitting the ball from both sides (Fig. 8.2). You will observe that in each hit the direction of the ball is changed. In this case also something is done to change the direction of motion of the body.

 

 

 

 

What is this something that changes the state of rest, or of uniform motion of a body? This something is called force. Thus, we can say that the force is something which when applied on a body changes or tends to change the state of rest or uniform motion of the body.
Kick, push, pull and hit are some of the different ways of applying force on a body. Each one is called an action. You must note that force is a vector quantity, because it is always applied along a particular direction and has magnitude.