Dec 112012
 

There are different types of force which are used by living beings in their day to day life. Force can be simply defined as the external agency that changes or tends to change the state of a body from rest to motion or from motion to rest. There are many types of force. Among them, frictional force or simply friction is also the one.

When a body is pulled on the surface of another body, then the opposite force which is developed in opposite direction of the applied force is called friction. Friction can be categorized into two major types which are:
1. Static or Limiting Friction
2. Dynamic or Kinetic Friction

  1. Static or Limiting Friction: Static or limiting friction is the type of friction which is the force of friction between a body and the surface of another body before actual motion of the body. This friction is represented by using Fs or Fl.
  2. Dynamic or Kinetic Friction: The force of friction between two surfaces when the body is in uniform or steady motion is called dynamic friction. It is also known as kinetic friction. This friction is constant during motion. It is represented by using Fd or Fk.

Coefficient of Static or Limiting Friction
Coefficient of static or limiting friction can be defined as the ration of static frictional force to the normal reaction between the two surfaces. It is represented by μs or μl.
If Fs represents the static frictional force, μs represents the coefficient of static frictional force and R is the normal reaction, then we can get the following expression:

If Fl represents the limiting frictional force, μl represents the coefficient of limiting frictional force and R is the normal reaction, then we can get the following expression:

Coefficient of Kinetic or Dynamic Friction
Coefficient of kinetic or dynamic friction can be defined as the ratio of dynamic frictional force or kinetic frictional force to the normal reaction. If Fk and R are kinetic frictional force and the normal reaction respectively, μk is the coefficient of kinetic friction. Then we can get the following expression:If Fd and R are the dynamic frictional force and the normal reaction respectively, μd is the coefficient of dynamic frictional force. Then we can get the following expression: