Elastic And Plastic Behaviour (T1)

Question 1

What is elastic behaviour?

Answer 1

It is a change in shape of an object that is completely reversible.

Elastic material do not break easily and tend to return to their original shape when the forces acting on them are removed.

Question 2

Describe plastic behaviour..

Answer 2

When an object changes shape permanently when a force is removed from it.

Question 3

Give some examples of elastic materials..

Answer 3

• the springs in a cars suspension

- the springs in a mattress

Question 4

Give some examples of plastic behaviour..

Answer 4

• when a can is crushed
• when a car is permanently dented after a collision
• when putty or plasticine is squashed

Question 5

Who was Robert Hooke and what is he well known for?

Answer 5

Robert Hooke was an English scientist who lived from 1635-1703.

He conducted a series of experiments measuring the increase in length (extension) produced by different load forces on springs.

He discovered that the extension of the spring is proportional to the load force.

This became known as “Hooke’s Law”.

Question 6

Define Hooke’s Law..

Answer 6

The extension of a spring is proportional to the load force

Question 7

What is the elastic limit of a spring?

Answer 7

When a spring reaches a point where Hooke’s Law no longer applies and it has changed shape permanently, it has reached its elastic limit. Its behaviour has gone from elastic to plastic.

Question 8

Why do rubber bands not follow Hooke’s Law?

Answer 8

Elastic bands are usually made from rubber.

If you stretch a rubber band with increasing load forces you get a graph that is not a straight line.

This shows that rubber bands do not obey Hooke’s Law.