N-Body Gravity Sandbox

关于这个模拟实验

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.

学生可以探索什么

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.

学习目标

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

教师常问的问题

Is it free to use?

Yes. It is completely free, needs no sign-up, and runs in any modern browser, including classroom whiteboards, tablets and phones. Just open the page and start.

Why do orbits get messy with three bodies?

With two bodies the orbits are tidy ellipses, but with three or more there is no general formula for the motion. Small changes grow quickly, so the orbits can become chaotic.

How do I launch a body?

Select a mass, click where you want the body, and drag before releasing. The drag sets the launch velocity. Keep Click places bodies switched on, and press Clear all to remove everything.

What keeps a planet in orbit?

Gravity pulls the planet toward the star while its sideways motion carries it onward. It keeps falling toward the star but keeps missing it, so it circles around.

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