# 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.*