Limiting Friction Explained – Laws of Limiting Friction
a force acting on the opposite direction to the motion of the body is known as friction or force of friction. Friction can be of the following two types.
- Static Friction 2. Dynamic Friction
The friction experienced by a body when at rest is known as static friction. The friction experienced by a body when at is known as dynamic friction. It is also known as kinetic friction. Kinetic friction are of the following two types :
a. sliding friction b. rolling friction
In this article we will discuss about the limiting friction. The friction experienced by a body , when its sliding over another body is known as sliding friction.
The friction experienced by a body , when balls or roller are interposed between two surfaces is known as rolling friction.
When a body just starts to slide over the surface of another one , the frictional force is developed between the surfaces. The maximum value of that frictional force is known as the limiting friction or static friction.
Laws of Limiting Friction
- The direction of limiting friction force is always the opposite of the motion of the body.
- The magnitude of the friction force is equal to the force that tends to move the body.
- The magnitude of the limiting friction always have a constant ratio with the normal reaction force which acts between the two surfaces.
- Limiting friction force depends on the roughness of the surface.
- Area between the surfaces is not responsible for the magnitude of the frictional force.
Angle of Limiting Friction
Say , a body ‘A’ is resting on a surface B. Now force P is applied to the body. The will not move untill the force P is equal to the limiting friction force F . Here
F = µ W = µ.Rn ( Here Rn is the normal reaction force. )
No relative motion will take place if P is not equals to F . And the force F will work opposite to the force P.
In the case limiting force – It will be in equilibrium under the actions of these three forces
- Weight of the body , W , Applied Force , P (horizontal), and Reaction force between surfaces A & B .
So for the equilibrium condition the reaction R will be equal to the weight W . P will be inclined at an angle ϕ to the reaction force Rn. Here ϕ is called the limiting angle of friction. The mathematical relation between the angle and the force is