Skip to content
Know.itKnow.it
Create an animated lesson
On request

This article is free to read. Creating a lesson uses your daily or stored credits; review the language and settings before starting.

What is friction?

ScienceLesson on requestFree to read

Quick answer

Friction is the force that resists motion when two surfaces rub against each other. It's why a sliding book slows and stops, why we can walk without slipping, and why rubbing your hands makes heat. No surface is perfectly smooth, so friction is everywhere.

Key things to understand

  1. A force that resists surfaces sliding past each other.
  2. Caused by tiny roughness and grip between surfaces.
  3. Lets us walk, grip, and brake.
  4. Turns motion energy into heat.

People also ask

What causes friction?
Microscopic roughness and molecular attraction between two touching surfaces resist their sliding.
Is friction useful or harmful?
Both — it lets us walk and brake, but also wears parts and wastes energy as heat, which is why machines use lubricants.
How do you reduce friction?
Smooth the surfaces, add a lubricant like oil, or use wheels and ball bearings to roll instead of slide.

Part of the guide: Everyday Machines →