State what is meant by the terms 'mass' and 'weight', and explain why an astronaut's weight changes when travelling from Earth to the Moon, whilst their mass remains the same.

Cambridge International IGCSE Physics (0625) — 1.3 Mass and weight · State and Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Mass is a measure of how much matter is in an object.
Weight is the gravitational force acting on an object (W = mg).
An astronaut’s mass remains the same because mass is independent of location.
On the Moon the gravitational field strength g is smaller than on Earth, so the weight W = mg is reduced, giving a lower weight on the Moon.

Examiner tips

  • Use the formula W = mg to link weight to mass and g.
  • Mention that mass is a scalar property, weight is a force.
  • Show the difference in g between Earth and Moon explicitly.

Common mistakes

  • Confusing mass with weight or vice versa.
  • Forgetting to state that mass does not change with location.
  • Using the wrong symbol for gravitational field strength (e.g., using G instead of g).

Mark scheme (4 marks)

  1. Mass is a measure of how much matter is in an object
  2. Weight is the gravitational force acting on an object (due to a gravitational field acting on the object's mass)
  3. The gravitational field strength (g) is different / smaller on the Moon than on Earth
  4. Weight depends on gravitational field strength (W = mg), so weight changes; mass does not depend on gravitational field strength so it stays the same

Key terms in this question

mass · weight

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