If we increase the applied force, a stage comes, when the body is just at the verge of moving over the other.
The static friction at this stage is obviously maximum.
This maximum-value of static friction is called limiting friction.
When we increase the applied force slightly beyond limiting friction, the actual motion starts.
This does not mean that friction has disappeared.
It only means that the applied force is now greater than the force of limiting friction.. The force of friction at this stage is called kinetic friction or dynamic friction. Kinetic friction is always slightly less than the limiting friction.
This is because, once the motion starts actually, inertia of rest has overcome.
Also, when motion has actually started, irregularities of one surface have little time to get locked again into the irregularities of the other surface.
Friction is defined as the resistance offered by the surfaces that are in contact when they move past each other.
Types of Friction
There are four categories of Friction- static friction, sliding friction, rolling friction, and fluid friction.
Sliding Friction
In Sliding Friction, the weight of the sliding object calculates the amount of sliding friction present between the two objects. The sliding friction is supposed to be greater as the pressure exerted by the heavy object on the surface it slides over is comparably more.
Rolling Friction
Friction between a circular object and the surface is called as Rolling Friction. It is required to overcome sliding friction is more than the force required to overcome the rolling friction.
Static Friction
Friction that keeps an object at rest without initiating any relative motion between the body and the surface is termed as Static Friction. For example, a parked car resting on the hill, a hanging towel on the rack. The maximum force of static friction is directly proportional to the normal force.
Fluid Friction
Fluid Friction is the kind of friction that is exerted by the fluid on the object that is moving through a fluid.
