A level revision

Key terms

You need to be familiar with the following key terms:

Stiffness

Stiffness is the resistance of a material to deformation. The stiffer a material is the less it will stretch for a given force.

Elastic and plastic

A material is said to be elastic if it returns to its original shape and size when the force is removed. Conversely, a material is said to be plastic if it does not return to its original dimensions.

Most materials are elastic up to a point, known as their elastic limit. Beyond this point they become plastic.

Ductile

A material is ductile if it can be shaped without breaking. A ductile material will undergo deformation before breaking.

Hardness

A material is said to be hard if it cannot easily be scratched or damaged.

Brittle

A material is brittle if it fractures when under stress with little or no deformation, for example glass when dropped onto the floor shatters as it is brittle. Brittle materials obey Hooke's law until they snap. A stress-strain graph of a brittle material is therefore just a straight line.

Toughness

Toughness descirbes how well a material resists fracturing when under stress. It is the area under a stress-strain graph.