N-Body Gravity Sandbox

Students choose a mass from moon to star, click to place a body and drag before releasing to give it a velocity. Gravity acts between all bodies, so they can build a star with a planet in circular orbit, a small system with one button, or a chaotic three-body dance. Trails show paths, and readouts show body count, total and kinetic energy, next mass and the number of merges. Bodies that touch combine. The sim shows that orbits are falling paths shaped by F = G m1 m2 / r squared. Teachers can ask for stable orbits.

• Choose 200 (star), click near the centre, then place a 1 (moon) body and drag to throw it sideways.
• Adjust the drag length until the moon stays in a near-circular orbit around the star.
• Press Add a small system and watch several bodies orbit with Trails switched on.
• Throw a body straight at the star and watch the Merges readout when they touch.
• Turn off Click places bodies to orbit the camera, and press Clear all to start again.

1. 1Describe how gravity pulls every body toward every other body.
2. 2Relate launch speed to whether an orbit is circular, elliptical or escapes.
3. 3Explain why systems with three or more bodies can become chaotic.
4. 4Observe energy and mass changes when bodies merge.

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