Physics / Mechanics

# Frictional Force

Friction or frictional force is the force that is generated when two bodies or surfaces have relative motion with each other and this force opposes the relative motion between them. Friction depends on the nature of two surfaces.

## Types of Friction

There are three types of frictions namely, (i) Static friction (self sustaining force), (ii) Kinetic or Dynamic or Sliding friction and (iii) Rolling friction.

• The Static friction is the force that is exerted by one body on another when there is no motion in between them. In Static friction, the magnitude of frictional force increases with the magnitude of applying force. The maximum value of static friction that a surface can exert on the body with which it is in contact is called Limiting friction.

• Frictional force, F = μR, where 'μ' is coefficient of friction and 'R' is the normal reaction on the body from the surface on which it lies.

• Sliding friction is the frictional force that opposes the movement of a body which slides over another body. Sliding friction is always less than the limiting friction.

• Rolling friction is the frictional force that is generated when a body rolls over another body and this force opposes the rolling motion. Rolling friction is always less than the sliding friction.

• Friction is a necessary evil. We are able to walk on a surface because of friction. It is easy to walk on a rough surface than on a smooth surface because of higher frictional force exerted by the rough surface.

• Polishing reduces friction to a certain extent but if exceeded, the friction again increases. Friction can also be reduced to a great extent when proper lubricants are used.