Deformation of Solids

Hooke’s law
The amount by which an object is stretch is proportional to the amount of force applied, assuming the elastic limit has not been exceeded. An object stretched beyond its elastic limit will become permanently deformed.

Hooke’s Law (as long as the elastic limit has not been exceeded)

Force = Extension x Spring Constant

Spring Constant (Nm-1)




Graphical Solutions


Elastic and plastic materials

Brittle and Ductile materials


Spring Combinations


Experiment to give the Young Modulus of a wire.

Note this is the only experiment that could be asked about in the exam.

Diameter of wire
Micrometer in several places and an average used

Length of wire
Meter rule for a wire greater than 1 meter

Repeat on unloading as well as loading to ensure the material doesn’t exceed its elastic limit

Vernier scale repeated on loading/unloading and a mean used

The following will need to be calculated:

Final step
Plot a stress-Strain graph and draw a line of best fit. Calculate the gradient using a tangent to give the Young Modulus.