Elastic potential energy

Stretch or compress

A stretched or compressed spring stores elastic potential energy. Work done deforming it increases this store.

Extension is the increase in length

Extension = stretched length − original length. A spring growing from 10 cm to 14 cm has extension 4 cm = 0.04 m.

Worked example

A spring has k = 200 N/m and extension 0.10 m.

Square the extension. 0.10² = 0.01.

The equation applies when the limit of proportionality has not been exceeded: force and extension are proportional. Do not confuse this with a promise that every extension is safe.

Challenge · changes

At fixed spring constant, doubling extension makes the stored energy four times larger. At fixed extension, doubling k doubles stored energy.

When released, a spring can transfer energy mechanically to a moving object.