3.1.16Movement and Interactions

Breaking Force — AQA GCSE Combined Science Synergy 8465 - Physical Sciences Revision Notes & Topical Questions

5 min read 6 parts Lesson 17 of 59

0%read

Part 1 of 4Forces change shape

Stretching and compressing

Stretching and compressing A single force can only move an object; to change its shape, at least two forces must act,
- such as a pull at each end of a spring.
Pulling lengthens a spring (stretching) and pushing shortens it (compressing).

Elastic deformation

Elastic deformation An object that returns to its original shape when the forces are removed has been elastically deformed.

Inelastic deformation

Inelastic deformation If the shape stays changed after the force is removed, the object has been inelastically (plastically) deformed.

Quantity	Symbol	Unit
Force applied	F	newton, N
Spring constant	k	newton per metre, N/m
Extension	e	metre, m
Equation	F = k × e	valid only below the limit of proportionality

1Small load

Small load Extension is directly proportional to force and the spring returns to its original length.

2Limit of proportionality

Limit of proportionality Beyond this point the graph of force against extension curves;
- the spring is no longer following F = k × e.

3Permanent stretch

Permanent stretch Past the elastic limit the spring will not fully recover its original length.

4Breaking

Breaking At a high enough force the material fails and snaps; this force is the breaking force.

Stretched spring

Work done

Work done Work done in stretching a spring is stored as elastic potential energy if the spring behaves elastically.

Calculating energy

Calculating energy E_e = ½ × k × e², with energy in joules, k in N/m and e in m.
Area under a straight-line force–extension graph also gives this energy.

Comparing materials

Comparing materials A stiffer spring has a larger k, so it needs more force for the same extension.
A brittle material snaps with very little extension; a ductile one stretches a lot first.

Term	Meaning
Extension	The increase in length of a spring or material compared with its original length.
Spring constant	The force needed per unit extension; a measure of the stiffness of a spring.
Limit of proportionality	The point beyond which extension is no longer directly proportional to force.
Elastic deformation	A change of shape that is reversed when the force is removed.
Breaking force	The force at which a material or object snaps or fails.

Using the total length of a spring as e; e is the extra length beyond its original length.

Applying F = k × e to a spring that has gone past its limit of proportionality.

Leaving extension in centimetres when k is in N/m.

Confusing elastic deformation (shape returns) with inelastic deformation (shape stays changed).

Last updated: 20 October 2026