Physics and Chemistry

Energy, Motion, and Force

Why is a lubricant, such as oil, often used to counter the force of friction?

What is friction?

Friction is defined as the force that resists motion when the surface of one object slides over or comes in contact with the surface of another object. The three laws that govern the friction of an object at rest and the surface with which it is in contact state:

  • Friction is proportional to the weight of an object.
  • Friction is not determined by the surface area of the object.
  • Friction is independent of the speed at which an object is moving along a surface provided the speed is not zero.

Although friction reduces the efficiency of machines and opposes movement, it is an essential force. Without friction it would be impossible to walk, drive a car, or even strike a match.

Lubricants, such as oil, are used to reduce friction. For example, in machines consisting of metal parts, the continuous rubbing of the parts together increases the temperature and creates heat. To prevent serious wear and damage to the machines, grease and oil are applied to reduce the friction.


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