Gravity & Orbits
Click and drag to launch a planet. Watch the dance.
Every object in space pulls on every other object. Heavy things pull harder. The moon stays near Earth not because Earth has a string attached — but because the Earth is always pulling the moon toward it, and the moon is always moving sideways fast enough to miss. That's an orbit.
Why does my planet just spiral into the star?
Probably not enough sideways speed. An orbit is the balance between gravity pulling you in and your tangential velocity making you 'miss.' Drag a longer line to launch faster.
Why does the three-body simulation never repeat?
Three or more gravitating bodies are mathematically chaotic — tiny differences in initial conditions blow up over time. There's no closed-form solution. This is the actual three-body problem from physics.
What integration scheme does this use?
Semi-implicit Euler — fast and stable enough for visualization, though it slowly drifts energy over long runs. Real astrophysics simulations use leapfrog or symplectic integrators.
Is the gravity strength realistic?
No — G is dialed up so things move on a human-watchable timescale. The relationships between mass, distance, and force are the same as reality; only the global scale is altered.