Friction

The force which opposes the relative motion of any body which is in contact with another body is called friction. Amount of friction can be different that depends on the movement of the body as follows :

• Static Friction : This is the force which restricts the movement when object is in resting state. This static friction increases when the applied force increases and reaches to a maximum point when body (mass/block) is about to move, this maximum force is called critical friction or the limiting friction.
• Kinetic friction : The friction force which is applied when the body is in motion. Kinetic friction is always less than the limiting or critical friction.

Key Factors –

1. Friction is proportional to the contact area between the body.
2. Friction depends on the nature of contact surfaces (roughness in creases friction).
3. Kinetic friction is independent of relative speed of bodies.
4. Kinetic friction is less than the limiting friction.

There are two different type of friction can be classified based on the kind of movement : Rolling and Centripetal friction.

Rolling friction acts when a body rolls over the surface of other body, while Centripetal force acts when body travels along a circular path.

Body in Equilibrium : When the resultant of all forces acting on a body is zero then the body is said to be in equilibrium. A equilibrium body must be in either rest or in a uniform motion. Equilibrium of the body can be of many types :-

• Stable equilibrium : If a body is in equilibrium position and a slight force is applied on it and body has tendency to regain it’s position, it is said to be in stable equilibrium. In this case the center of gravity should be at minimum height and vertical line passing through the center of gravity of the body should pass through the base of the body.
• Unstable equilibrium : If slight force is applied on the body which is in equilibrium and body moves in the direction of displacement and doesn’t regain its original position, the equilibrium is said to be unstable equilibrium. In this equilibrium, the center of gravity of the body is at the highest position.
• Neutral equilibrium : If on slight displacement from equilibrium position body has no tendency to come back to it’s original position or to move in the direction of displacement. In this case, the center of gravity is remains at the same height.