Mechanical

# 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.

1. 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.

# Limiting 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 Basic Mechanical Engineering is a small endeavor for the mechanical engineering students and fresh graduates. All the articles are written by mechanical "rocking" engineers \m/