Materials, Density, Pressure and Deformation
Relating bulk properties and force-extension behaviour to stress, strain, Young modulus, elastic energy, density and pressure.
How to study A-level Physics
Define the system, represent the physics, select a justified model, calculate transparently, then test the result against units, limits and evidence.
Core concepts
Concept 1
Stress and strain separate geometry from material response; Young modulus is the gradient in the linear elastic region.
Exam cue: Use original length and cross-sectional area unless the specification context states otherwise.
Concept 2
The area under a force-extension graph represents work done in deforming the sample.
Exam cue: Distinguish proportional limit, elastic limit and breaking point.
Concept 3
Density and pressure connect microscopic or structural features to measurable bulk behaviour.
Exam cue: Match each graph area or gradient to its variables and units.
Risk pitfalls and guardrails
Using extension where strain requires extension divided by original length.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Assuming elastic behaviour must be linear.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Confusing stiffness of a sample with Young modulus of a material.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Memory anchors
Stress
Stress is force divided by cross-sectional area.
Strain
Strain is extension divided by original length and has no unit.
Young Modulus
Young modulus is stress divided by strain in the linear elastic region.
Elastic Energy
Elastic energy transferred is the area under the force-extension graph.
Density
Density is mass divided by volume.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
A metal block has mass 0.54 kg and volume 2.0 × 10⁻⁴ m³. What is its density?
A material of density 800 kg m⁻³ occupies 0.015 m³. What is its mass?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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