A rubber band and a steel rod are both described as elastic materials. Explain what the term elastic means in this context, and describe how the behaviour of the rubber band differs from that of the steel rod when a gradually increasing tensile force is applied to each.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Elastic means the material returns to its original shape/length when the force is removed.
The steel rod obeys Hooke’s Law: the extension is directly proportional to the applied tensile force within its proportionality limit.
The rubber band does not obey Hooke’s Law: its extension is not proportional to the applied force.
The steel rod has a much greater stiffness, so a much larger force is required to produce the same extension as the rubber band.
Both materials return to their original length/shape when the force is removed, provided the elastic limit has not been exceeded.
The steel rod obeys Hooke’s Law: the extension is directly proportional to the applied tensile force within its proportionality limit.
The rubber band does not obey Hooke’s Law: its extension is not proportional to the applied force.
The steel rod has a much greater stiffness, so a much larger force is required to produce the same extension as the rubber band.
Both materials return to their original length/shape when the force is removed, provided the elastic limit has not been exceeded.
Examiner tips
- Use the term ‘elastic’ to describe recovery of shape; mention Hooke’s Law for steel; contrast with non‑linear behaviour of rubber; note stiffness difference; remember the elastic limit clause.
Common mistakes
- Confusing elastic with plastic deformation; stating that rubber obeys Hooke’s Law; ignoring the elastic limit condition; not specifying proportionality for steel.
Mark scheme (5 marks)
- Elastic means the material returns to its original shape/length when the force is removed
- The steel rod obeys Hooke's Law / extension is directly proportional to force (within the limit of proportionality)
- The rubber band does not obey Hooke's Law / extension is not proportional to force
- The steel rod has a much greater stiffness / requires a much larger force for the same extension compared to the rubber band
- Both materials return to their original length / shape when the force is removed (provided the elastic limit has not been exceeded)
Key terms in this question
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain and Describe" question →
- Decode the mark scheme abbreviations →
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