Why does weight change with location (e.g., Moon) while mass does not?

• A. Mass remains constant; weight changes with gravitational field strength; on the Moon gravity is weaker, so weight is less.
• B. Mass changes with location; weight remains constant.
• C. Mass increases with altitude; weight stays the same.
• D. Mass and weight both change with location equally.

Answer: (A)

Mass is the amount of matter in an object, so it stays the same wherever you are. Weight, on the other hand, is the force of gravity acting on that mass, which depends on how strong gravity is at your location. The relationship is W = m × g, where g is the local gravitational acceleration. On the Moon, g is weaker than on Earth, so the same mass experiences a smaller gravitational pull and thus a smaller weight. For example, a person with a mass of 70 kg has a weight that’s about 70 × 1.6 ≈ 112 Newtons on the Moon versus about 70 × 9.8 ≈ 686 Newtons on Earth. So weight changes with location because gravity changes, while mass remains constant.