What causes motion?

In my previous posts, we have discussed motion, the different types of motion and some physical quantities associated with the motion of a body. All these have been discussed without regard for the actual cause of motion. Have you ever wondered why a body at rest would move, a moving body continues in uniform motion or why a body at rest remains at rest?

 

For example, a block would remain at rest on a plane table unless it is acted upon by an agent who can change its position. A body moving at uniform speed in a straight line would also continue until an agent pushes or pulls it away from its path. 

Therefore, the only agent known to change the position of a body at rest or a body moving in uniform motion in a straight line is the force.

Hence, force can be defined as an agent that changes or tends to change the state of rest or of uniform motion in a straight line of a body.

Effects of force;

• it can move a body
• it can change the direction of motion of a body
• it can make a moving body to slow down or stop moving
• it distorts or changes the shape of a body
• it can increase the length of a spring and also bend a rod etc.

Types of Force

1. Contact forces: These are forces which requires contact with the body to which they are applied. Examples are: push, pull, reaction, tension and frictional forces. 

2. Non contact forces (force fields): These are forces which do not require contact with the body to which they are applied. Their influence can only be felt on the body within the region of these forces. Their actions are felt at a distance. Examples are: gravitational force, electric force, magnetic force etc.