Friction Force Calculator

What Is Friction Force?

Friction is a force that opposes the relative motion or tendency of motion between two surfaces in contact. It is essential for everyday life — without friction, you could not walk, drive, or grip objects.

There are two main types of friction: static friction (which prevents an object from starting to move) and kinetic friction (which opposes ongoing sliding motion). You can find the coefficient of friction by dividing friction force by normal force.

How to Calculate Friction Force

Friction Force Formula

Where:

• F_f = friction force (N)
• μ = coefficient of friction (dimensionless)
• F_n = normal force (N)

On a flat, level surface, the normal force equals the weight of the object: F_n = mg, where m is the mass and g = 9.81 m/s². On an inclined surface at angle θ, the normal force is F_n = mg × cos(θ).

Worked Example

A 50 kg box sits on a concrete floor. The coefficient of kinetic friction between the box and floor is 0.6. What friction force resists sliding?

F_n = 50 × 9.81 = 490.5 N
F_f = 0.6 × 490.5 = 294.3 N

Friction on Inclined Surfaces

On an incline at angle θ, the normal force decreases to mg × cos(θ), reducing friction. Meanwhile, a component of gravity (mg × sin(θ)) pulls the object down the slope. The object slides when the gravitational component exceeds the maximum static friction force.