What is the difference between mass and weight?

• A. Mass measures gravity; weight measures inertia.
• B. Weight is how much matter an object contains.
• C. Mass is the amount of matter in an object; weight is the gravitational force on that mass, which can vary with location.
• D. Mass equals weight on Earth only.

Answer: (A)

Mass is the amount of matter in an object. Weight is the gravitational force acting on that mass. Because gravity varies by location, weight can change while mass stays the same. The relationship is W = m × g, so your mass stays constant whether you’re on Earth, the Moon, or in space, but your weight changes with the local gravity.

For example, a 60 kg person on Earth experiences about 60 × 9.8 ≈ 588 newtons of weight, while on the Moon (where gravity is weaker) they’d weigh about 60 × 1.6 ≈ 96 newtons. Inertia—the resistance to changing motion—is related to mass, but weight is not inertia; weight is the gravitational pull on mass.