Module 1 · What gravity is
Two masses
Interactive 5 min
Gravity pulls any two masses together with a force F = G·m₁·m₂ / r² [1]. Between the Sun and the Earth that is about 3.5 × 10²² newtons, and it is exactly equal and opposite on both bodies. The Sun is about 333,000 times heavier than the Earth [2], so the same force barely moves it.
Try this. Compare the two arrows. They have the same length. Why does the Earth still move so much more than the Sun?
Sources: [1] CODATA recommended value: Newtonian constant of gravitation (NIST); [2] Sun Fact Sheet (NASA GSFC NSSDC)
Step 1 of 1
What is gravity?
Gravity is the attraction between any two masses: F = G · m₁·m₂ / r² — stronger with more mass, weaker with the square of the distance. Here are just two bodies. The arrows show the pull each exerts on the other: exactly equal and opposite (Newton’s 3rd law), about 3.5 × 10²² newtons. The Sun is ~333 000× heavier, so the same force barely moves it but flings the Earth around. This one rule is the whole story — next we’ll see it even built these bodies.
Text version of this interactive
What is gravity?
Gravity is the attraction between any two masses: F = G · m₁·m₂ / r² — stronger with more mass, weaker with the square of the distance. Here are just two bodies. The arrows show the pull each exerts on the other: exactly equal and opposite (Newton’s 3rd law), about 3.5 × 10²² newtons. The Sun is ~333 000× heavier, so the same force barely moves it but flings the Earth around. This one rule is the whole story — next we’ll see it even built these bodies.
About this interactive
- Licence
- MIT
- Credits
- © 2026 Mateusz Wojczal. Earth texture: Solar System Scope, CC BY 4.0. Three.js (MIT). Inter and Roboto Mono (SIL OFL 1.1).
- Source
- https://github.com/ulams-dev/ulams/tree/main/demo-content/gravity