Grade 11 · Physics
Friction
Why it matters
Static and kinetic resistive forces.
Core20m readingPrerequisite: Gravity & Universal Gravitation
What is friction in physics?
Short answer
Friction is a force that opposes the relative motion or attempted motion between two surfaces in contact. Static friction prevents an object from starting to move and can vary up to a maximum; kinetic friction acts on a sliding object and is roughly constant. Its size depends on the normal force and the roughness of the surfaces, expressed by a coefficient of friction.
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Frequently asked questions
- What is the difference between static and kinetic friction?
- Static friction resists the start of motion and varies up to a maximum; kinetic friction acts once sliding begins and is roughly constant.
- What does friction depend on?
- The normal force pressing the surfaces together and the coefficient of friction set by their materials and roughness.