Lesson 5 of 8

Stretching springs

Goal: Describe how a spring stretches as the force on it increases.

Puzzles for this lesson

The bigger the force on a spring, the more it stretches. Up to a limit, doubling the force doubles the extension.

Extension is how much longer the spring has become. Extension = stretched length − original length.
Hooke’s law: the extension is directly proportional to the force. A graph of extension against force is a straight line through the origin.
There is a limit. Past the limit of proportionality the extension is no longer proportional to the force, and the line curves. A spring pulled much too far does not go back to its original length.

Hooke’s law is why the scale on a newton meter is evenly spaced.

Your turn

This lesson’s activity starts here in a moment.

I can measure an extension.I can say that extension is proportional to force and read this from a graph.

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Extension How much longer a spring gets when it is stretched

Hooke’s law The extension of a spring is proportional to the force on it

Limit of proportionality The point past which a spring no longer follows Hooke’s law

Directly proportional Doubling one quantity doubles the other: the graph is a straight line through the origin

For teachers: AQA 3.1.3 · Pearson Edexcel 43.1