Gravity & Weight
Year 7 🚀 Forces & Motion Distinguish mass from weight; understand gravitational field strength.
🌍 Mass vs Weight
Mass is the amount of matter in an object (measured in kg). It stays the same everywhere. Weight is the gravitational force on an object (measured in Newtons).
| Property | Mass | Weight |
|---|---|---|
| Unit | kg | N |
| Measured with | Balance | Newton meter |
| Changes with gravity? | No | Yes |
⬇️ The Weight Equation
Weight depends on mass and the gravitational field strength of the planet.
⚡ Weight Formula
$$W = mg$$
$W$ = weight (N) · $m$ = mass (kg) · $g$ = gravitational field strength (N/kg)
On Earth g = 10 N/kg On Moon g = 1.6 N/kg On Mars g ≈ 3.8 N/kg
🌙 Gravity in Space
Gravitational field strength decreases with distance from a planet. The further away, the weaker the pull.
An astronaut's mass stays 70 kg on Earth and the Moon — but their weight changes from 700 N to 112 N!
Ready to test yourself? Click the Quiz tab above to answer questions on this topic!
🌍 Weight Calculator