# Physics KS3/KS4: Hooke's Law

In this short video Professor Brian Cox highlights the effect of forces in changing the shape of an object. Hooke’s Law is described using the example of a spring.

The initial linear relationship between force and extension is described, illustrating that the extension is proportional to the force exerted on a spring. It also highlights that the spring returns to its original length when the force is removed.

The video then describes the effect of overstretching a spring and explains that the spring will no longer return to its original length if the bonds within its molecules have been permanently broken by overstretching.

### Teacher Notes

Points for discussion:
Investigation of Hooke’s Law is a Required Practical in AQA, Edexcel and OCR GCSE specifications.

This practical develops Apparatus and Techniques Physics 1 & 2 (DfE GCSE subject content guidance, Appendix 4).

At KS3, students need to be aware of Hooke’s Law, particularly the linear relationship between force and extension.

Students may not use a spring at KS3 but may investigate the stretching of, for example, elastic bands or sweet laces.

From previous experience, students will be aware that a force extends a spring and that the spring can be overstretched.

This video provides an explanation for these observations and uses key terminology that students should know, for example ‘proportional’.

Suggested activities:
This video could be used after students have investigated Hooke’s Law as a way of reinforcing the linear and non-linear relationships between force and extension, and to explain their observations in terms of molecular bonds.

Alternatively, it could be used as an opportunity to revisit the practical and the learning from it.

At KS4, students could progress to calculating a spring constant where the relationship is linear, or to calculate the work done in stretching.

At KS3, students may not need to explore the non-linear relationship between force and extension in over-stretching, but experience will have told them that we can overstretch an object and some students may find it helpful to have this explained.

### Curriculum Notes

Suitable for Combined Science and Physics GCSE in England, Wales and Northern Ireland and at National 4 and 5 in Scotland.

Also may be suitable for KS3. Although a spring may not be the example used at KS3, the idea that forces cause objects to stretch is explored and a linear relationship identified.