The Inverse-Square Law

How gravity weakens with distance

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• $F = Gm_1m_2/r^2$: every mass attracts every other mass.
• Double the distance and the force drops to a quarter.
• The same gravity that drops apples keeps the Moon in orbit.

Steps

1. The apple and the Moon
2. Newton’s law of gravitation
3. Twice as far
4. Newton’s Moon test
5. Who pulls harder?
6. Two people