GCSE Physics · AQA 8463 · Topic 4.5.3
Forces and elasticity
Key points
- To stretch, squash or bend an object you need more than one force.
- Elastic deformation: the object returns to its original shape when the forces are removed. Inelastic (plastic) deformation: it does not.
- Hooke's law: the extension is directly proportional to the force, , as long as the limit of proportionality is not passed. is the spring constant in N/m.
- On a force–extension graph, the straight part shows Hooke's law; the curve after it shows the limit has been passed.
- Energy stored in a stretched spring: . It equals the work done in stretching it (below the limit of proportionality).
- Required practical: measure extension of a spring for different hanging weights, using a ruler level with a pointer.
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Springs, rubber bands, bungee cords and car suspensions all change shape when forces act on them. This sub-topic is about how much an object stretches for a given force, when it springs back, and how much energy it stores while stretched.
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