Measurement
Weight vs mass
Mass is how much stuff. Weight is how hard gravity pulls — different things.
Mass measures how much matter — the same on the Moon. Weight measures how hard gravity pulls — less on the Moon.
Try this
9.8
weight = mass × g (for a 70 kg person) = —
Same matter, different pull
Mass (kilograms) is how much *stuff* you're made of — it never changes. Weight (newtons) is how hard gravity pulls on that stuff — drag the slider above and watch the weight change while the mass stays put.
Your turn
An astronaut massing 80 kg lands on the Moon (g ≈ 1.6 m/s²). What's their Moon weight, and their Moon mass?
Recap
- Mass = amount of matter (kg), the same everywhere.
- Weight = gravitational force (N), depends on local g.
- Bathroom scales read force but show it as kg — a useful fib that only works on Earth.
In everyday talk we use 'weight' loosely to mean mass — but in physics they're different.