 # Friction Force Formula

Friction is a repelling force when one body is slipping through a surface. Friction is because of the contact between two surfaces. If the frictional force is great, the movement of objects through the surface is not smooth. All through this movement, the kinetic energy is transformed to heat energy. The friction force is a derived force and not like gravitation i.e. a fundamental force.

## Formula of Friction Force

The formula for friction force is,

$$\begin{array}{l}F_f = \mu F_n\end{array}$$

Where,

• Ff is the friction
• μ is the coefficient of friction force
• Fn is the normal force

It is a vector quantity.

### Friction Force – Solved Examples

Let us answer some problems with a friction force.

Problem 1: An object of mass 10 kg is moving through a surface. Compute the friction force if the coefficient of friction is 0.2?

Known variables are,
m = 10 kg and μ = 0.2
The friction force formula is,
Ff = μFn
Fn can be computed as,
Fn = mg
= 10×9.81 = 98.1 N
So, Ff = 0.2×98.1 = 19.62 N

Friction force Ff is 19.62 N

Problem  2: Calculate the friction force of a 5 kg body which is moving through a surface with a friction coefficient 0.3?

Known variables are,
m = 5 kg and μ = 0.3
The friction force formula is,
Ff = μFn
Fn can be computed as,
Fn = mg
= 5×9.81 = 49.05 N
So, Ff = 0.3×49.05 = 14.715 N

Friction force Ff is 14.715 N

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