# 7.1.1 Hooke's Law

### Tensile Force

• Forces don’t just change the motion of a body, but can change the size and shape of them too. This is known as deformation
• Forces in opposite directions stretch or compress a body
• When two forces stretch a body, they are described as tensile
• When two forces compress a body, they are known as compressive

Diagram of tensile and compressive forces

#### Tensile Strength

• Tensile strength is the amount of load or stress a material can handle until it stretches and breaks
• Here are some common materials and their tensile strength:

Tensile strength of various materials

#### Exam Tip

Remember to read the questions carefully in order to not confuse the terms ‘tensile stress’ and ‘tensile strain’.

### Hooke's Law

• A material obeys Hooke’s Law if its extension is directly proportional to the applied force (load)
• The Force v Extension graph is a straight line through the origin
• This linear relationship is represented by the Hooke’s law equation

Hooke’s Law

• The constant of proportionality is known as the spring constant k

#### Exam Tip

Double check the axes before finding the spring constant as the gradient of a force-extension graph. Exam questions often swap the load onto the x-axis and length on the y-axis. In this case, the gradient is not the spring constant but 1 ÷ gradient is.

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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