Elasticity

You should be able to give examples of the forces involved in stretching, bending

or compressing an object.

You should be able to explain why, to change the shape of an object (by stretching,

bending or compressing), more than one force has to be applied – this is limited to

stationary objects only.

You should be able to describe the difference between elastic deformation and

inelastic deformation caused by stretching forces.

The extension of an elastic object, such as a spring, is directly proportional to the

force applied, provided that the limit of proportionality is not exceeded:

force = spring constant × extension

F = ke

force, F, in newtons, N

spring constant, k, in newtons per metre, N/m

extension, e, in metres, m

This relationship also applies to the compression of an elastic object, where ‘e’

would be the compression of the object.

A force that stretches (or compresses) a spring does work and elastic potential

energy is stored in the spring. Provided the spring is not inelastically deformed,

the work done on the spring and the elastic potential energy stored are equal.

You should be able to:

 describe the difference between a linear and non-linear relationship

between force and extension

 calculate a spring constant in linear cases

You should be able to interpret data from an investigation of the relationship

between force and extension.

You should be able to calculate work done in stretching (or compressing) a spring

(up to the limit of proportionality) using the equation:

elastic potential energy =

1

2

× spring constant × extension2

Ee =

1

2

ke

2

You should be able to calculate relevant values of stored energy and energy

transfers.