The Tidal Force

Two bulges, not one

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Tidal force is the difference in gravity across a body.
• It falls off as $\frac{1}{d^3}$, faster than gravity itself.
• It stretches the Earth into two bulges: towards and away from the Moon.

Steps

1. Gravity that varies
2. Stretching the Earth
3. An inverse cube
4. Twice as far
5. Why two bulges?
6. Turning under the bulges
7. Sun versus Moon