Weighing Worlds

From a lab balance to Jupiter

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

• Cavendish’s torsion balance measured G in 1798.
• Surface gravity gives a planet's mass: $M = gR^2/G$; Earth's density shows a dense core.
• Any orbit reveals the central mass: $M = 4\pi^2 r^3 / (GT^2)$.

Steps

1. Measuring G
2. A tiny force
3. Weighing the Earth
4. Earth’s density
5. Weighing Jupiter
6. Weighing the Sun