Friction and drag
Friction is a force that opposes sliding between two surfaces. Drag is the force that opposes movement through air or water.
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Analogy
Rub your hands together and they warm up. Hold your hand out of a car window and you feel the air push back.
In practice
Brakes use friction to slow a wheel. Streamlined shapes cut drag.
Practice
Flashcards
- Name one use of friction.Tyres gripping the road, or brakes slowing a wheel.
Questions people ask
Is friction always bad?
No. Friction lets tyres grip the road, lets you walk without slipping, and lets brakes work. It becomes a problem when it wastes energy as heat or wears parts out, which is why machines use oil to reduce it. Without any friction you could not even hold a pencil.
What makes air resistance bigger?
Higher speed and a larger, less streamlined shape both increase it. Doubling a car's speed more than doubles the drag. This is why cyclists crouch and cars have smooth curved shapes. A smaller front area means less air to push out of the way.