GCSE Physics · Edexcel 1PH0 · Topic 15A

Elastic and inelastic deformation

Key points

To change the shape of an object you need more than one force (stretching, compressing or bending).
Elastic deformation: the object returns to its original shape when the forces are removed. Inelastic (plastic): it does not.
Hooke's law: $F = kx$ , where $k$ is the spring constant (N/m) and $x$ is the extension (m). It applies up to the limit of proportionality.
A force–extension graph is a straight line through the origin while Hooke's law holds; the gradient is $k$ .
Energy stored in a stretched spring: $E = \frac{1}{2}kx^2$ , which equals the area under the force–extension graph.
Core practical: hang masses on a spring, measure extension with a ruler at eye level, and plot force against extension.

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Stretch a spring gently and it springs back; stretch it too far and it stays longer for good. This sub-topic explains the difference, introduces Hooke's law and shows how to calculate the energy a stretched spring stores.

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