Friction
TYPES OF FRICTION
There are three types of frictional forces
i. Static friction ii. Dynamic friction iii. Rolling friction
* STATIC FRICTION : The frictional force, which is effective before motion starts between two surfaces in contact with each other, is known as static friction
Note : 1) Static frictional force is a variable and self adjusting one
2) The maximum frictional force when the body is ready to start is called limiting frictional force
* DYNAMIC OR KINETIC FRICTION : The frictional force, which is effective when two surfaces in contact with each other are in relative motion with respect to each other, is known as dynamic friction.
* ROLLING FRICTION : The frictional force, which is effective when a body rolls or rotates on a surface is known as rolling friction.
It is due to deformation at the point of contact.
LAWS OF FRICTION
Prof.Coulomb, after extensive experiments, gave some laws of friction. It is known as laws of Coulomb friction or dry friction.
* Friction opposes relative motion between two surfaces in contact and is always tangential to the surface of contact.
* Friction depends on the nature of the two surfaces in contact i.e., nature of materials, surface finish etc.
* Friction is independent of the area of contact between the two surfaces
* Friction is directly proportional to the normal reaction acting on the body.
* F\(
\alpha
\)N \(
\Rightarrow
\) F = \(
\mu
\)N Where \(
\mu
\)= coefficient of friction