17.0 HOOKE'S LAW

Hooke's Law describes the behaviour of elastic materials when they are stretched or compressed. It is fundamental to understanding springs, shock absorbers, and countless mechanical systems. This chapter covers the concept of elasticity, the law itself, the spring constant, and how springs behave when combined in series or parallel.

17.1 ELASTICITY

Elasticity is the property of a material that allows it to return to its original shape and size after the deforming force is removed. Materials that have this property are called elastic materials.

17.1.1 Stretching a Spring

When a force is applied to a spring, it stretches. The amount of stretch (or compression) is called the extension (x). Extension is defined as:

Extension = New length – Original length

For a spring that is compressed, the term compression is used, but the mathematics is similar.

17.1.2 Elastic Limit

If you hang increasing weights on a spring, it stretches more and more. However, there is a limit beyond which the spring will not return to its original length when the weights are removed. This point is called the elastic limit.

• Below the elastic limit: The spring behaves elastically – it returns to its original length when the force is removed.
• At the elastic limit: The spring is stretched to the point where it just begins to suffer permanent deformation.
• Beyond the elastic limit: The s