Friction

 

When you rub two solids together usually with rough surfaces, you will observe that they will not slide freely over each other. This is as a result of the roughness of their surfaces which tends to oppose the motion of one surface over the other. This is as a result of the effect of friction.

Friction can be defined as a force which acts between the surface of two solids in contact. It tends to hinder the movement of one of the solids over the other.

Friction can also be said to be a force of opposition which acts tangentially to the surface of separation between the two bodies in contact.

Thus, for the two bodies to be able to move one over the other, frictional forces must be overcome. Friction also slows down the moving body or even bring it to a stop when the force producing the motion is withdrawn.

Types of friction

Consider the diagram above, an amount of force is needed to move the above body over the other depending on the weight of the body on top, the maximum force that must be overcome (usually the weight of the body) before the body can just begin to move over the other is called Static or Limiting Friction.

Now, when the body begins to move over the other with uniform speed, the force of friction that tends to oppose its motion must be overcome. This force of friction that must be overcome in order to keep the body with uniform speed is called Kinetic or Dynamic Friction.

Laws of Friction

1. Friction tends to hinder the motion between two surfaces in contact. Its also acts in an opposite direction to the motion.

2. Frictional force acts in the same extent as the force which starts the motion.

3. It depends on the nature of the surfaces in contact such as; the type of surface- rough, smooth, polished, wet, dry, etc.

4. Friction does not depend on the area of the surfaces in contact.

5. Frictional force, F varies with the normal force acting on the two surfaces together, i.e. it is proportional to the normal reaction, R

F α R

Or F = μR

The constant μ is known as the coefficient of friction.

Thus, μ = F/R

Coefficient of friction (μ) is defined as the ratio:

μ = frictional force F/ Normal reaction R