6 - Materials

Question 1

What is Hooke’s law?

Answer 1

The force (F) needed to stretch a spring is directly proportional to the direction (ΔX) of a spring from it’s natural length, provided the elastic limit has not been reached.

F ∝ Δx

F = k Δx
where k = spring constant (force required to produce an extension of one metre)
Unit (k) = Nm⁻¹

Question 2

What is the elastic limit?

Answer 2

Up to a certain extension, if the force is removed the spring will return to it’s original length. Spring is behaving elastically.

If the critical extension (elastic limit) is exceeded, the spring will become permanently stretched. Spring is behaving plastically and Hooke’s law is ignored.

Question 3

What is elastic strain energy?

Answer 3

When a spring or wire is stretched potential energy is stored.

This form of potential energy is called elastic strain energy.

Work done = average tensile force x extension
W = ½Fx

E = ½kx²