Topic 15 - Elasticity only

How can objects change shape?(3)

bending

stretching

compressing

How do forces act when an object is compressed?

In opposite directions

towards the object

How do forces act when an object is stretched?

In opposite directions

away from the object

How do forces act when an object is bent?

In opposing directions

at different points on the object

Two types of distortion?

elastic

inelastic

elastic distortion

When objects return to their original shape when the stretching force is removed

examples of elastic distortion

Rubber bands

Fabrics

Steel springs

inelastic distortion

When objects remain stretched and do not return completely to their original shape even when the stretching force is removed

examples of inelastic distortion

Plastic

Clay

Glass

Hooke’s law

The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality

limit of proportionality

the point beyond which the relationship between force and extension is no longer directly proportional

Hooke’s law equation

F = k × x

F = force in newtons (N)

k = spring constant in newtons per metres (N/m)

x = extension in metres (m) - the symbol x can represent either the extension or compression of an elastic object

What does the spring constant measure?

how stiff a spring is

What happens to stiffness as spring constant increases?

increases

Spring extension equation

final length - original length

elastic potential energy

the energy stored in an elastic object when work is done on the object

elastic energy equation

E = ½ kx2

E = elastic potential energy (energy transferred in stretching) in joules (J)

k = spring constant in newtons per metre (N/m)

x = extension in metres (m)

What are the conditions to use the elastic potential energy?

Only applicable to springs that have not been stretched past their limit of proportionality