Science
What is Mass?
Mass is the amount of matter in an object — a measure of how much 'stuff' it contains. It stays the same everywhere in the universe, unlike weight, which is the force of gravity on that mass and changes with location.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains mass.
Key things to understand
- 1Mass measures how much matter an object contains, in kilograms (kg).
- 2It's constant — your mass is the same on Earth, the Moon, or in deep space.
- 3Mass resists changes in motion: more mass needs more force to accelerate it (inertia).
- 4Weight is different — it's the force of gravity on a mass, and it changes with location.
- 5Mass is measured with a balance (comparing masses), not a spring scale (which measures weight).
Frequently asked questions
- What's the difference between mass and weight?
- Mass is how much matter is in an object (constant everywhere); weight is the force of gravity pulling on that mass, which changes with location. You'd weigh less on the Moon but have the same mass.
- Does mass change on the Moon?
- No. Your mass stays the same anywhere. Only your weight changes — on the Moon you'd weigh about one-sixth of your Earth weight because its gravity is weaker.
- What unit is mass measured in?
- The kilogram (kg) is the standard scientific unit of mass; grams and tonnes are also common.