Friction

What is Friction?

Within Physics, which covers forces, energy, waves, electricity, magnetism, light and space explained through motion and experiments, this topic explains Friction. Physics topics explain how things move, push, heat up and carry energy, so each one here pairs a definition with a live model you can change.

Check that you can explain Friction in your own words and give one example from everyday life. If you can do that, you have understood the core idea.

Understanding Friction explains how the physical world behaves, from sport and transport to electricity and medicine.

Friction in detail

Friction is a contact force that opposes the relative motion, or the tendency of motion, between two surfaces. It arises from microscopic roughness and bonding between surfaces and acts parallel to them. Static friction prevents sliding up to a limit, and kinetic friction acts once sliding begins.

Friction produces heat and wear but is also essential for walking, gripping and braking. It can be reduced by lubrication, smoother surfaces or wheels, and increased by rougher tyres or treads. Friction does work against motion, which is why moving objects slow down unless a force keeps them going.

How the interactive helps you understand Friction

Watch the force arrows in the interactive. Use any sliders or buttons it offers to change the values and see how the force arrows responds.

Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Friction.

Real-life uses and examples

• Use Friction to make sense of a practical and its results.
• Answer “explain” questions by linking Friction to a clear cause and effect.
• Predict what a ball, car or circuit will do with Friction before you do the calculation.

Common mistakes to avoid

• Mixing up Friction with a related quantity that has different units.
• Forgetting that some quantities, such as force or velocity, also have a direction.
• Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.