Materials

AQA A level Physics

Breaking Stress

The maximum stress that an object can withstand before failure occurs

Brittle

An object that shows very little strain before reaching its breaking stress

Elastic Behaviour

Object returns to its original shape when the deforming forces are removed. The object will not be permanently deformed

Elastic Limit

The force beyond which an object will no longer deform elastically, and instead deform plastically. Beyond the elastic limit, when the deforming forces are removed, the object will not return to its original shape

Hooke’s Law

The extension of an elastic object will be directly proportional to the force applied to it up to the object’s limit of proportionality

Plastic Behaviour

Object will not return to its original shape when the deforming forces are removed. The object will be permanently deformed

Spring Constant

The constant of proportionality for the extension of a spring under a force. The higher the spring constant, the greater the force needed to achieve a given extension

Stiffness

A measure of how difficult it is to stretch a given object

Tensile Strain

The ratio of an object’s extension to its original length. It is a ratio of two lengths and so has no unit

Tensile Stress

The amount of force acting per unit area. Its unit is the Pascal (Pa)

Young Modulus

The ratio of stress to strain for a given material. Its unit is the Pascal (Pa)

Springs in series

K_T = K₁ + K₂

(opposite to resistors in series)

Springs in parallel

1/K_T = 1/K₁ + 1/K₂

(opposite to resistors in parallel)

Elastic strain energy per unit volume equation

½ stress x strain

(area under stress-strain graph)

Yield Point

Beyond the elastic limit this point is reached where a small increase in stress causes a massive increase in extension (strain)

Material now behaves plastically

Ductile

Easily and permanently stretched (e.g. copper)

Tough

Stores a lot of energy when deformed (e.g. kevlar)

Strong

A material with a high UTS

Hard

Can scratch or indent, and withstands being scratched

Soft

Can be easily crushed, cut, bent, or scraped