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Everything that has mass (everything made of stuff) pulls on everything else. You and your desk pull on each other too, but that pull is far too small to feel. The Earth has an enormous mass, so its pull on you is strong. The more mass, the stronger the pull; the further away, the weaker it gets.

Mass is how much stuff you are made of, and it stays the same everywhere. Weight is how hard gravity pulls on you. On the Moon gravity is about 1.6 m/s², compared with 9.8 m/s² on Earth, so you would weigh about one sixth as much. On Mars (3.7 m/s²) you would weigh a bit more than a third, and on Jupiter (23.1 m/s²) almost two and a half times as much.

Long ago people thought heavy things fall faster. In 1586 the Flemish engineer Simon Stevin and his friend Jan Cornets de Groot dropped two lead balls of different weights from a church tower in Delft. They landed at almost the same time. (A famous story says Galileo did this from the Leaning Tower of Pisa, but there is little proof that he did.)

Experiment: The parachute test

1. Cut three squares from the plastic: 10 cm, 20 cm and 30 cm wide.
2. Tape a 25 cm thread to each corner, and tie the four threads to the same weight.
3. Choose one drop height (for example 2 metres, measured). Always drop from that height.
4. Drop each parachute three times and time how long it takes to reach the floor.
5. Work out the average time for each size. Which parachute falls slowest?

Parachute	Time 1 (s)	Time 2 (s)	Time 3 (s)	Average (s)
10 cm
20 cm
30 cm

Questions

1. Explain the difference between mass and weight.

2. On Earth, a bathroom scale shows 30 kg for a child. About what would the same scale show on the Moon?

3. Which parachute fell most slowly? Why?

4. Why do astronauts float, even though there is gravity in space?

Sources for every fact on this sheet: echoesof.science/school/gravity/sources/

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