PhysicsMechanicsUniversity
IBUndergraduate

Kinetic friction Calculator

Kinetic friction is the resistive force that opposes the relative motion of two surfaces in contact.

Use the free calculatorCheck the variablesOpen the advanced solver
Open Advanced Calculator
This is the free calculator preview. Advanced walkthroughs stay in the app.
Result
Ready
Kinetic friction force

Formula first

Overview

This equation defines the magnitude of the kinetic frictional force as the product of the coefficient of kinetic friction and the normal force acting between the surfaces. It applies specifically when surfaces are already in motion relative to one another, distinguishing it from static friction. The force acts in the direction opposite to the velocity of the object relative to the surface.

Symbols

Variables

= Kinetic friction force, = Coefficient of kinetic friction, = Normal force

Kinetic friction force
Coefficient of kinetic friction
dimensionless
Normal force

Apply it well

When To Use

When to use: Use this equation when an object is sliding across a surface and you need to calculate the resistive force opposing that motion.

Why it matters: Understanding kinetic friction is essential for analyzing energy dissipation, mechanical efficiency, and the dynamics of moving systems in engineering and physics.

Avoid these traps

Common Mistakes

  • Assuming the normal force is always equal to mg, even on inclined planes.
  • Confusing the coefficient of kinetic friction with the coefficient of static friction.
  • Applying the formula to objects that are not yet moving.

One free problem

Practice Problem

A 10 kg block is sliding across a horizontal surface. If the coefficient of kinetic friction is 0.2 and the normal force is 98 N, what is the magnitude of the kinetic friction force?

Coefficient of kinetic friction0.2 dimensionless
Normal force98 N

Solve for:

Hint: Multiply the coefficient of kinetic friction by the normal force.

The full worked solution stays in the interactive walkthrough.

References

Sources

  1. Halliday, D., Resnick, R., & Walker, J. (2014). Fundamentals of Physics (10th ed.). Wiley.
  2. Young, H. D., & Freedman, R. A. (2020). University Physics with Modern Physics (15th ed.). Pearson.
  3. Halliday, D., Resnick, R., & Walker, J. (2013). Fundamentals of Physics.
  4. Young, H. D., & Freedman, R. A. (2015). University Physics.
  5. NIST CODATA
  6. IUPAC Gold Book
  7. University Physics (OpenStax)
  8. Halliday, Resnick, and Walker's Principles of Physics