Friction Coefficient Calculator

Created by Michael Darcy
Reviewed by Dominik Czernia, PhD candidate
Last updated: Aug 19, 2022

If you want to know the amount of resistance due to friction between two bodies, then our friction coefficient calculator can help you. Read on if you'd like to learn how to calculate the coefficient of friction and find out whether there's a separate equation for the static friction coefficient and the kinetic one. We will also explain the reason behind the coefficient of friction unit, or rather, the lack of it.

What is the coefficient of friction?

Why can you slide easily on ice but stumble if you try to repeat it on asphalt? The answer is friction. When you try to move two objects against each other, it acts as a resisting force. It varies for different surfaces - this is where solving for friction coefficient is helpful.
This quantity is the ratio between the friction force and the normal force between two bodies. It's constant for two given surfaces, meaning that no matter how much force you put into sliding a sled on snow, the coefficient of kinetic friction formula will always give you the same result.
Wait... kinetic friction? What if the objects don't move? Is there an equation for static friction coefficient too? The answer awaits below!

Formula for the coefficient of friction

How to calculate the coefficient of friction? The simplest way is to use the coefficient of friction equation:

μ=FN,\mu = \frac{F}{N},

where:

  • μ\mu - Friction coefficient;
  • FF - Friction force; and
  • NN - Normal force acting on the body.

Since dimensions on the right-hand side cancel out, we can see that the coefficient of friction has no units. So this is how to find the coefficient of friction; pretty easy, isn't it?

✅ Another pleasant fact about it: there's only one formula for the coefficient of friction, no matter if the problem is kinetic or static.

How to find coefficient of friction

Now that we know what solving for friction coefficient gives us, let's summarise the necessary steps along the way:

  1. Determine the magnitudes of normal force and friction.
  2. Substitute these values for NN and FF in the coefficient of friction equation, respectively.
  3. When noting the result, remember that the coefficient of friction unit is none!

Now you can use this number to predict what resistance you can expect when sliding these materials against each other!

To learn more about friction and how it makes pushing a fridge so difficult, check out our other tools:

For those of you interested in friction affecting fluids inside a pipe:

FAQ

Can a coefficient of friction be greater than 1?

Yes, although in most applications, the friction coefficient is between 0 and 1. An exception can be, for example, silicone rubber - you can see it by trying to rub an eraser against a piece of acrylic.

How does mass affect the coefficient of friction?

Mass doesn't affect the friction coefficient, regardless of whether we're considering the coefficient of static friction formula or the kinetic case. Since both friction and normal force are proportional to mass, it cancels out when we divide them to calculate the coefficient of friction.

What is the friction coefficient if the friction is 0.3 N and the normal force is 50 N?

Solving for friction coefficient:

  1. Note that the normal force is 50 N and the friction is 0.3 N.
  2. Divide the friction by the force: 0.3 N / 50 N = 0.006.
  3. The quotient, 0.006, is the friction coefficient.
Michael Darcy
Normal force (N)
lbf
Friction (F)
lbf
Friction coefficient (μ)
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