1.31 Describe elastic behaviour as the ability of a material to recover its original shape after the forces causing deformation have been removed.

Elastic behavior is the ability of a material that can return to its normal shape after forces that caused deformation have been removed.

Eg when an (initially elastic) object no longer does this, it has reached elastic limit.

Figure 1: A spring, for example, shows elastic behavior.

Figure 2: A spring that has been stretched past its elastic limit. This will not return to its original shape :(

1.30 Understand that the initial linear region of a force-extension graph is associated with Hooke’s law

In a force extension graph, like the one shown below, the linear region demonstrates Hooke's Law. It shows that there is a direct correlation between extension and force applied; they increase at the same rate.

The elastic limit is where the graph curves. It means that when the object reaches this point, it will no longer spring back into its original shape.

1.29 Describe experiments to investigate how extension varies with applied force for helical springs, metal wires and rubber bands

When a force is applied to a wire, rubber band or spring, they extend (and usually spring back into shape). To investigate how the force applied affects extension, you could conduct the following experiment, or something similar:

1. Attach a spring to a newton meter. Measure the length of the spring.
2. Attach a 10g mass and measure the spring length again.
3. Keep increasing the mass attached to the spring by 10g until you reach a given amount (for this example, let's say 80g) and measuring the new spring length.
4. Calculate the extension (how long the spring stretched by subtracting the original length from the new length)
5. Plot a graph

When you plot the graph, you should see that the extension increases with the force applied (which would've been shown by the newton meter)

Note that when the graph curves, the elastic limit of the object (in this case, the spring) has been reached.