Weight and mass
Mass is the amount of matter in an object, in kg. Weight is the pull of gravity on it, in N. Weight = mass x gravitational field strength (W = mg).
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Analogy
Mass is how much stuff you are made of. Weight is how hard a planet pulls on it.
Example
mass = 60 kgg on Earth = 10 N/kgW = 60 x 10 = 600 Ng on Moon = 1.6 N/kgW = 60 x 1.6 = 96 N
In practice
On the Moon your mass is the same but your weight is about one sixth as big.
Practice
Flashcards
- What is weight and how is it calculated?Weight is the pull of gravity on a mass. W = mg.
- Why can mass and weight not be swapped?Mass is matter in kg and never changes. Weight is a force in N and depends on gravity.
Questions people ask
What is the difference between mass and weight?
Mass is how much matter an object has, measured in kilograms. It stays the same everywhere. Weight is the gravitational pull on that mass, measured in newtons. It changes with the planet, so an astronaut weighs less on the Moon but has the same mass.
What value of g should I use?
On Earth, gravitational field strength is about 9.8 N/kg. School questions often round it to 10 N/kg, and the question will say which to use. It is the force of gravity on each kilogram, so a 1 kg mass weighs about 10 N.