GCSE Physics resources
AQA GCSE Forces
Add loads to a spring or wire, measure extension from the unloaded length and plot force against extension. Increase the load carefully, remove loads for repeats where appropriate and identify the straight-line region.
Start here
Add loads to a spring or wire, measure extension from the unloaded length and plot force against extension. Increase the load carefully, remove loads for repeats where appropriate and identify the straight-line region.
Before you revise
Choose an answer from memory. Your result tells you what to watch for in the guide.
Core revision guide
Force and Extension Required Practical questions become manageable when the central model, evidence and exam method are kept together. Read the explanation, test the misconception and then apply the idea without looking back.
Add loads to a spring or wire, measure extension from the unloaded length and plot force against extension. Increase the load carefully, remove loads for repeats where appropriate and identify the straight-line region.
Measure the unloaded length first, then subtract it from every loaded length to find extension. Add masses carefully and wait for oscillations to stop. A force-extension graph shows the proportional region; the first clear departure from a straight line is the limit of proportionality.
Hooke’s law: F = ke (N, N/m, m). Choose each relationship from the physical change described, convert quantities into compatible units and keep the unit beside the final answer.
Misconception clinic
Read each belief, say what is wrong with it, then compare your correction.
Tempting idea: Plotting total length rather than extension.
Use instead: Add loads to a spring or wire, measure extension from the unloaded length and plot force against extension. Increase the load carefully, remove loads for repeats where appropriate and identify the straight-line region.
Tempting idea: Adding masses without converting to force.
Use instead: Measure the unloaded length first, then subtract it from every loaded length to find extension. Add masses carefully and wait for oscillations to stop. A force-extension graph shows the proportional region; the first clear departure from a straight line is the limit of proportionality.
Tempting idea: Calling any curve the elastic limit.
Use instead: Explain zero reading, eye-level measurement, control of the apparatus and how the graph identifies the limit of proportionality.
Retrieval practice
Worked examples
These examples expose the difference between a secure find the limit of proportionality method and the common error “Plotting total length rather than extension.”.
Extension = 48 mm.
Force = 2.94 N.
Extension is proportional to force up to about 4 N, the limit of proportionality.
Exam precision
Do this: Explain zero reading, eye-level measurement, control of the apparatus and how the graph identifies the limit of proportionality.
Independent practice
Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.
Marking guidance: Award one mark for the precise statement shown in the model answer.
Model answer: Force/load applied.
Marking guidance: Award one mark for the precise statement shown in the model answer.
Model answer: Extension of the spring/wire.
Marking guidance: Award up to 3 marks for distinct physics points joined into a clear cause-and-effect chain.
Model answer: Extension is the change from original length, not total loaded length.
Marking guidance: Award one mark for the precise statement shown in the model answer.
Model answer: Keep the same spring, wait for oscillations to stop and read scale at eye level.
Marking guidance: Award up to 3 marks for distinct physics points joined into a clear cause-and-effect chain.
Model answer: To avoid damaging the spring and to obtain stable readings.
Marking guidance: Award one mark for the precise statement shown in the model answer.
Model answer: Use a pointer/set square or a scale with finer divisions and repeat readings.
Questions pupils ask
Add loads to a spring or wire, measure extension from the unloaded length and plot force against extension. Increase the load carefully, remove loads for repeats where appropriate and identify the straight-line region.
Plotting total length rather than extension. Measure the unloaded length first, then subtract it from every loaded length to find extension. Add masses carefully and wait for oscillations to stop. A force-extension graph shows the proportional region; the first clear departure from a straight line is the limit of proportionality.
Useful next steps