Stress and strain
Cambridge A-Level Physics (9702) · Unit 6: Deformation of solids · 8 flashcards
Stress and strain is topic 6.1 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 6 — Deformation of solids , alongside Elastic and plastic behaviour. In one line: A tensile force is a force that tends to stretch or lengthen an object, while a compressive force is a force that tends to squash or shorten it. Dividing either force by the cross-sectional area gives the tensile or compressive stress.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 8 flashcards — 6 definitions, 1 key concept and 1 calculation — covering the precise wording mark schemes reward. Use the 6 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
'tensile force' and 'compressive force'
A tensile force is a force that tends to stretch or lengthen an object, while a compressive force is a force that tends to squash or shorten it. Dividing either force by the cross-sectional area gives the tensile or compressive stress.
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Understand that tensile (stretching) or compressive (squashing) forces cause deformation; forces and deformations are treated in one dimension only.
- Understand the meaning of load, compression, extension and the limit of proportionality, and use these terms.
- Recall Hooke's law and use it.
- Recall the spring constant formula k = F / x and use it.
- Define the Young modulus, stress and strain, and use these terms.
- Describe an experiment that measures a metal's Young modulus using a wire made of the metal.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Stress and strain
- › Use the exact syllabus terminology for definitions: stress is force per unit cross-sectional area; strain is extension per unit original length.
- › For identical springs in parallel, divide the total force by the number of springs to find the force acting on, and extension of, each.
Define 'tensile force' and 'compressive force'.
A tensile force is a force that tends to stretch or lengthen an object, while a compressive force is a force that tends to squash or shorten it. Dividing either force by the cross-sectional area gives the tensile or compressive stress.
Define 'load' and 'extension'. How are they related?
Load refers to the force applied to an object. Extension refers to the increase in length of an object due to the applied load. Load is directly proportional to extension within the limit of proportionality.
State Hooke's Law.
Hooke's Law states that the extension (or compression) of a spring is directly proportional to the force applied to it, provided the limit of proportionality is not exceeded. Mathematically, F = kx, where F is force, k is the spring constant, and x is the extension.
What is the formula for calculating the spring constant (k)?
The spring constant (k) is calculated using the formula k = F / x, where F is the force applied to the spring and x is the resulting extension (or compression). It measures the stiffness of a spring.
Define 'stress' and 'strain'.
Stress is the force per unit area acting on a material (σ = F/A). Strain is the fractional change in length of a material due to stress (ε = ΔL/L). Both are important in characterizing material behavior.
Define 'Young modulus'.
The Young modulus (E) is a measure of a material's stiffness or resistance to elastic deformation under stress. It is defined as the ratio of stress to strain in the elastic region: E = stress/strain.
Outline the key steps in an experiment to determine the Young modulus of a metal wire.
Measure the original length (L) and diameter (d) of the wire. Apply increasing loads (F) and measure the corresponding extensions (ΔL). Calculate stress (F/A) and strain (ΔL/L) for each load. Plot a stress-strain graph; the gradient of the linear region gives the Young modulus (E).
What is the 'limit of proportionality'?
The limit of proportionality is the point beyond which Hooke's law is no longer obeyed. Beyond this point, the extension of a material is no longer directly proportional to the applied load, and the material may experience permanent deformation.
Review the material
Read full revision notes on Stress and strain — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 6 — Deformation of solids
Stress and strain sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Stress and strain deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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