Enter the coefficient of friction and the normal force between two objects to calculate the force due to friction. This calculator is for static or kinetic friction; use the correct coefficients.

Friction Formula

The following formula can be used to calculate a friction force.

Force of Friction (F) = U * N
  • Where U is an empirical measurement of the two contacting properties, known as the coefficiency of friction.
  • N is the normal force between the two objects. The normal force acts perpendicular to the surfaces.

To calculate the friction force, multiply the coefficient of friction by the normal force.

What causes friction?

Another factor that influences the coefficient of friction is the fractality of it, which is a parameter that looks at the asperities of the surfaces. This subject is a little beyond our expertise, and we will leave that to research further if you are interested.

The coefficient of friction ranges from just above 0 to above 1 for very “sticky” materials. For most dry materials, this value is between .3-.6. A value of 0 is impossible to achieve because that means there would be no friction at all, which is not something that scientists have found in nature yet.

This value also relies on variables like temperature, velocity, and atmosphere, along with many others.

How to calculate the friction force between two objects

The following example is a step-by-step guide on how to calculate the force due to friction between two objects or surfaces.

How to calculate friction force

  1. First, the normal force between the two surfaces must be calculated.

    For this example, we are going to assume the friction we are calculating is between a flat block and the ground. Therefore, the normal force is going to simply be the gravitational force on the object. Let’s say the block weighs 30 newtons.

  2. Next, the coefficient of friction between the surfaces must be determined.

    The coefficient of friction between two surfaces is a difficult value to measure. In most cases, it’s done empirically, or in other words, through physical experiments. This example won’t go into detail about how that is done. Instead, it will just assume that this value is .5.

  3. Finally, enter information into the formula or calculator presented above.

    F = u * N = .5 * 30 = 15 N. The force due to friction between these surfaces is 15 newtons.

  4. Analyze the results

    The last step in this process is to analyze the results. This is a key step in any science problem or question. Analyzing the result to see if it make sense will help catch many errors in the future.


What is Friction?

The force of friction is a measure of the total force that arises from the phenomena described above. Friction is directly proportional, also known as linearly proportional, to both the coefficient of friction and the normal force.

What is a coefficient of friction?

The coefficient of friction is a scalar quantity, and the science behind how it’s measured is quite interesting. This coefficient depends on material deformation characteristics, surface roughness, and chemical bonding between atoms in the materials.