Key learning points

1. Doubling the stiffness of a spring doubles the energy it has because it is stretched.
2. The spring constant is measured in newtons per metre (N/m).
3. Doubling the extension of a spring increases the energy it has because it is stretched by four times.
4. The energy a spring has because it is stretched equals 1/2 × spring constant × (extension)².

Keywords

• Elastic store - If an elastic object is stretched, compressed or bent out of shape, there is energy in the elastic store.

• Compress - To make something smaller using forces, e.g. a spring gets shorter when it is compressed.

• Extension - The increase in length from the original length of a spring when it is stretched.

• Spring constant - A measure of how stiff a spring is and how hard it is to stretch or compress.

Common misconception