# A student presses down on a foam cushion and then removes the force. The foam returns to its original shape. The student then presses much harder and removes the force. This time the foam does not return to its original shape. Explain why the foam behaves differently in each case.

> AQA GCSE Physics (8463) — 4.5.3 Forces and elasticity · Explain · 4 marks

## Mark scheme (4 marks)

1. In the first case the foam undergoes elastic deformation
2. Elastic deformation means the foam returns to its original shape when the force is removed
3. In the second case the force applied exceeds the elastic limit
4. This causes plastic deformation, so the foam does not return to its original shape

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