A student takes an object to the Moon, where the gravitational field strength is weaker than on Earth. State and explain what happens to the mass and the weight of the object when it is on the Moon compared to when it is on Earth.

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

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

Model answer (4 marks)

The mass of the object remains unchanged on the Moon.
Mass is a measure of the amount of matter in the object and does not depend on the gravitational field.
The weight of the object decreases on the Moon.
Weight is the force of gravity on the object (W = m·g) and the gravitational field strength g is smaller on the Moon.

Examiner tips

  • State the mass stays the same first, then explain why; then state weight decreases and give the formula W = m·g with g smaller.
  • Use the exact terms ‘mass’, ‘weight’, ‘gravitational field strength’, and ‘W = m·g’.
  • Keep the answer to two short sentences – one for mass, one for weight.

Common mistakes

  • Confusing mass with weight and saying mass changes.
  • Using the wrong formula for weight (e.g., W = g only).
  • Omitting the reason that g is smaller on the Moon.

Mark scheme (4 marks)

  1. Mass stays the same / is unchanged on the Moon
  2. Because mass is a measure of the amount of matter in the object / mass does not depend on gravitational field strength
  3. Weight decreases / is less on the Moon
  4. Because weight depends on gravitational field strength / weight = mass × gravitational field strength, and g is smaller on the Moon

Key terms in this question

mass · weight · gravitational field strength

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