Force de frottement - Qu'est-ce que le frottement ?

In this article, you will learn the definition of friction, laws of friction, types and effects of friction, advantages and disadvantages of friction or frictional force.


When a solid slides over another solid surface, there is always resistance in motion. The resistance is called Friction. Friction is, therefore, the resistance that is experienced when two surfaces come in contact and move relative to each other. It can hinder the motion of an object or prevent it from moving at all.



  1. Friction opposes motion.
  2. It does not depend on the area of the surfaces in contact.
  3. It depends on the nature of the surfaces.
  4. Friction force F is proportional to the normal reaction N

The force of friction between an object and a surface is equal to a constant number multiplied by the force the object exerts directly on the surface. The constant number is called the coefficient of friction between the two materials. The force the object exerts directly on the surface is called the Normal force and it is abbreviated N.

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In the case of a level surface, the normal force is equal to the weight of the object. i.e.  N = W = Mg


  1. Static Friction – This friction occurs between stationary objects.
  2. Sliding or Dynamic Friction – This type of friction exists between two objects as they move relative to each other.


Friction serves both as an advantage and disadvantage to society. Ever wondered why tires of our automobile are threaded? It is for traction.


  1. The effect of friction enables us to safely walk, run, and drive or ride a car, motorcycles, and bicycles.
  2. Friction between nails and woods will prevent the nail from sliding out and keeps the building standing.
  3. Friction between a matchstick and a matchbox enables the match to light up when it is struck.
  4. The sharpening of a knife-edge with a file or grinding stone is made possible as a result of friction.
  5. Friction helps brake system of our automobile to function.
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  1. Friction opposes motion and therefore slows down movement.
  2. It causes a gradual wearing off of machine parts when they rub against themselves thereby reducing the efficiency of the machine.
  3. It causes heating.


Why Friction cannot be practically eliminated, it can be reduced greatly. Two major ways by which friction can be reduced are;

  • Through the lubrication of machine parts.

A lubricant, whether in the form of oil or grease, when applied in between two surfaces in contact, reduces the roughness between them. This prevents excessive heat generation that could have resulted in wear and tear.

  • Through the use of rollers or ball bearings.
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Rollers or Ball bearing are sometimes attached to the base of some heavy machines to aid the movement of such machine easily. This also helps the frictional force between these objects and the ground.

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