Physics AS Materials Unit 2

The extension of a spring is directly proportional to the load or force acting upon it.

F = ke 

Mass / Volume

Force / Cross-sectional Area

Note: Cross sectional area = (pi x diameter^2) / 4 

It is measured in Nm^-2 or Pa (Pascals) 

Change in Length / Original Length

It has no units, it is just a number. 

Stress / Strain

If you increase the force (load) on a material past the Elastic Limit, the material will become permanently elastically deformed, meaning it will no longer return to its original shape.

If you increase the Force (load) on a material past the limit of proportionality, then it will no longer obey Hooke's Law, however it will return to its original shape because the limit of proportionality is reached before the elastic limit.

Here the material suffers a large amount of plastic deformation without an extra force (load).

..It snaps suddenly when the force reaches a certain size, without plastically deforming.

0.5 x stress x strain

The maximum stress a material can withstand.