GCSE Physics · AQA 8463 · Topic 4.5.1
Forces and their interactions
Key points
- A scalar has magnitude only; a vector has magnitude and direction. Vectors can be drawn as arrows.
- Contact forces need objects to touch (friction, air resistance, tension, normal contact force). Non-contact forces act at a distance (gravity, magnetic, electrostatic).
- Weight is the force of gravity on a mass: , where is the gravitational field strength (about 9.8 N/kg on Earth). Weight acts at the centre of mass.
- Weight and mass are directly proportional. Weight is measured with a newtonmeter.
- The resultant force replaces all forces on an object. Forces in the same line are added or subtracted.
- (Higher tier) Forces can be resolved into two perpendicular components with a scale drawing; forces in equilibrium form a closed triangle.
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Before you can predict how anything moves, you need to describe the forces on it: how big they are, which way they act and what they add up to. This sub-topic sets out that toolkit, from vectors and weight to free body diagrams.
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