A cyclist wants to improve the efficiency of their bicycle. Explain how lubrication can improve the efficiency of the bicycle, and describe what happens to the energy that is wasted when no lubrication is used.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Friction acts between the moving metal parts of a bicycle's chain and gears. A cyclist applies oil to these parts before a long ride.
Model answer (4 marks)
Lubrication reduces the friction between the chain and the gears, so less of the cyclist’s input energy is lost as a waste energy transfer.
Because the frictional force is lower, less heat is produced at the contact surfaces.
Consequently a greater proportion of the cyclist’s input energy is converted into useful energy – mainly the kinetic energy of the bicycle and the rider.
If no lubrication is used, the high friction between the chain and gears turns the input energy into heat, which is transferred to the surroundings as thermal energy, reducing the efficiency of the bicycle.
Because the frictional force is lower, less heat is produced at the contact surfaces.
Consequently a greater proportion of the cyclist’s input energy is converted into useful energy – mainly the kinetic energy of the bicycle and the rider.
If no lubrication is used, the high friction between the chain and gears turns the input energy into heat, which is transferred to the surroundings as thermal energy, reducing the efficiency of the bicycle.
Examiner tips
- State the effect of lubrication on friction first, then link to heat loss and useful energy. Use terms like "waste energy transfer" and "thermal energy". Keep answer concise to fit 4 marks.
Common mistakes
- Confusing lubrication with a lubricant’s chemical composition rather than its effect on friction. Failing to mention that the wasted energy becomes heat or thermal energy.
Mark scheme (4 marks)
- Lubrication reduces the friction between moving parts / between chain and gears
- Less energy is transferred as a waste energy transfer (e.g. less heat produced at the surfaces)
- More of the input energy becomes useful energy transfer (e.g. kinetic energy of the bicycle)
- Without lubrication, wasted energy is transferred to the surroundings as heat / thermal energy (due to friction between the surfaces)
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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