# Friction and Types of Friction

### What is Friction ?

A force acting in the opposite direction to the motion of the body is called force of friction or simply friction.

### Different types of Friction

1. Static Friction
2. Dynamic Friction or Kinetic friction
1. Sliding friction
2. Rolling friction
1. Static Friction : The friction experienced by a body, when it is at rest is known as static friction.
2. Dynamic Friction : The friction experienced by a body, when it is in motion is called dynamic friction. It is also called as kinetic friction. Dynamic friction is further classified into two types.
1. Sliding Friction : The friction experienced by a body, when it slides over another body, is known as sliding friction.
2. Rolling friction : The friction experienced by a body, when balls or rollers are interposed between the two surfaces, is known as rolling friction.

1. It enables us to walk without slipping.
2. The breaks and tiers of our cars and bicycles depend on friction to function properly.
3. The ridges in the skin of our fingers and palms enable us to grasp and hold objects due to friction.
4. Nails and screws are held in wood by fiction.

1. The main disadvantage of friction is that it produces heat in various parts of machines. In this way some useful energy is wasted as heat energy.
2. Due to friction we have to exert more power in machines.
3. It opposes the motion.
4. Due to friction, engines of automobiles consume more fuel.
5. Friction reduces the efficiency of engine and other machines.

### Limiting Friction

The maximum value of frictional force, which comes into play, when a body just begins to slide over the surface of the other body, is known as limiting friction.

### Coefficient of Friction

It is defined as the ratio of limiting friction to the normal reaction between the two bodies.

1. Laws of Static Friction
1. The force of friction always acts in a direction opposite to that in which the body tends to move.
2. The magnitude of force of friction is exactly equal to the force, which tends the body to move.
3. The magnitude of the limiting friction bears a constant ratio to the normal reaction between the two surfaces.
4. The force of friction is independent of the area of content between the two forces.
5. The force of friction depends upon the roughness of the surfaces.
2. Laws of Dynamic Friction
1. The force of friction always acts in a direction, opposite to that which the body tends to move.
2. the magnitude of the kinetic friction bears a constant ratio to the normal reaction between the two surfaces.
3. For moderate speeds, the force of friction remains constant. But it decreases slightly with the increase in speed.