Calculate the force of friction between two surfaces given the normal force and the coefficient of friction.
Ratio
Friction Force (F)
50N
How is this calculated?
Friction Formula: F = μ × N
Where μ is the coefficient of friction and N is the normal force.
F = 0.5 × 100 N
F = 50 N
Share this result
About the Friction Calculator
Friction is the force that resists things sliding past each other. Whether you are dragging a heavy box across the floor or relying on your car's tires to stop on a wet road, friction is at work.
Mathematical Formula & Logic
Friction Force
F = mu * N
- F = Force of Friction (N)
- mu = Coefficient of Friction ()
- N = Normal Force (N)
Normal Force (Horizontal Surface)
N = m * g
- N = Normal Force (N)
- m = Mass (kg)
- g = Acceleration due to gravity (m/s^2)
Step-by-Step Example
A 500 N wooden crate on a wooden floor (coefficient of 0.3) requires 500 × 0.3 = 150 Newtons of force to keep sliding.
A car tire pressing into asphalt with 4,000 N of force (coefficient of 0.8) generates 4,000 × 0.8 = 3,200 Newtons of grip.
Reference Data & Values
normal force
coefficient
friction force
100
0.5
50
500
1.2
600
1000
0
0
0
0.8
0
9.80665
0.3
2.941995
Frequently Asked Questions
The formula for dry friction is F = μN, where F is the friction force, μ (mu) is the coefficient of friction, and N is the normal force.
Static friction is the force holding a stationary object in place. It is usually stronger. Kinetic friction is the force resisting an object that is already sliding. It is usually weaker.
Yes! A coefficient greater than 1 simply means the friction force is stronger than the normal force pressing the objects together. Silicone rubber on asphalt can have a coefficient greater than 1.
The normal force is the perpendicular force a surface exerts to support an object resting on it. On a flat horizontal floor, it is exactly equal to the object's weight (mass × gravity).
In standard high-school physics (the Coulomb model), no. The friction force depends only on the normal force and the materials, not on how large the contact area is.
It has no units! It is a dimensionless ratio of two forces (Friction Force divided by Normal Force).
The coefficient depends primarily on the materials of the two surfaces in contact and their roughness or smoothness.
Lubrication introduces a fluid layer between the surfaces, drastically lowering the coefficient of friction and reducing the resistance to motion.