Gravitational Field & Escape Velocity Lab
Pick a world, launch a rocket straight up and see whether it falls back or truly escapes, with the real field strength and escape speed live.
How to use: pick a world, then drag the launch speed slider and fire a rocket straight up. Watch whether it falls back, orbits, or truly escapes, and read the live gravitational field strength and escape velocity for that world.
Challenge 1: reach Earth escape velocity
Select Earth and set the launch speed to at least Earth's true escape velocity (about 11.2 km/s), then launch.
Challenge 2: match any world's escape speed
Pick any world, set the launch speed within 5% of that world's calculated escape velocity, and launch.
About the Gravitational Field & Escape Velocity Lab
Free gravitational field & escape velocity lab. Pick a world, launch a rocket straight up and see whether it falls back or truly escapes, with the real field strength and escape speed live. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for astronomy, the gravitational field & escape velocity lab runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Pick a world, launch a rocket straight up and see whether it falls back or truly escapes, with the real field strength and escape speed live. Use it to explore astronomy ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Gravitational Field & Escape Velocity Lab
- Use the controls to change Mass (× Earth mass), Radius (× Earth radius), Launch speed (km/s). The simulation reacts instantly.
- Press "🚀 Launch", "Reset flight", "📊 Compare all worlds", "Reset to defaults" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Launch from Earth at 8 km/s and watch it fall back, then try 11.3 km/s.
- Switch to the Moon and find how much lower its escape velocity is.
- Switch to Jupiter and see how much faster you must launch.
- Try the Sun preset and see just how enormous its escape velocity is.
Key ideas you can learn
- Surface gravity is g = GM/r²: it grows with mass and shrinks fast with radius.
- Escape velocity is v = √(2GM/r): it depends only on the mass and radius of the world, not on the rocket's own mass or launch direction.
- A launch below escape velocity is gravitationally bound and falls back (or would orbit if launched sideways); at or above escape velocity, the total mechanical energy is zero or positive and the object never returns.
- Jupiter's huge mass gives it a far higher escape velocity than Earth even though its surface gravity difference is smaller, because escape velocity depends on M/r under a square root while g depends on M/r².
Where this is used in the real world
Rocket engineers size every launch vehicle's required burnout speed around exactly this escape-velocity calculation, and it is why probes leaving the solar system need a gravity assist to reach solar-system escape speed.
Who is this simulation for?
Students, teachers and curious learners of all ages.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
Why doesn't the mass of the rocket matter for escape velocity?
Escape velocity comes from setting the kinetic energy per kilogram equal to the gravitational potential energy per kilogram; the rocket's mass cancels out of both sides, so a feather and a spacecraft need the same speed to escape a given world.
Why is the Moon's escape velocity so much lower than Earth's?
The Moon has both much less mass and a smaller radius than Earth; since v_esc = √(2GM/r), the much smaller M dominates and its escape velocity works out to about 2.4 km/s versus Earth's 11.2 km/s.
Is the Gravitational Field & Escape Velocity Lab free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Gravitational Field & Escape Velocity Lab work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.