Friction is the force that opposes one object sliding over another. Various factors effect the friction between two surfaces including:

  • the type of materials in contact
  • the amount of pressure being applied that forces them together
  • the texture of the surfaces in contact
  • the area of the surfaces in contact
  • whether lubricated or dry.

Coefficient of Friction

The amount of resistance to sliding of one object over another is called the coefficient of friction. A high resistance to sliding results in a high coefficient of friction.

Friction force may be expressed as:

Ff = µ N


Ff = friction force (N, lb)

µ = static (µs) or kinetic (µk) frictional coefficient.

N = normal force

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Copyright Laszlo Lipot.


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