Orbital Motion & Gravity Simulator
Launch a planet around a star and see circular, elliptical and escape orbits.
Drag the blue planet to move it. Drag the tip of the green velocity arrow to change how fast and in which direction it moves, then watch the new orbit.
About the Orbital Motion & Gravity Simulator
Free gravity and orbit simulator. Change the star's mass and the planet's launch speed to see circular, elliptical and escape orbits, with live period and eccentricity. Built for physics, the orbital motion & gravity simulator 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.
Launch a planet around a star and see circular, elliptical and escape orbits. Use it to explore physics ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Orbital Motion & Gravity Simulator
- Use the controls to change Star mass, Starting distance, Launch speed, Time speed. The simulation reacts instantly.
- Press "Launch again", "Pause" 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
- Set the launch speed to 1.00× for a circle.
- Raise it to 1.3× to get an ellipse.
- Go above 1.41× to escape.
- Double the star's mass and see the period change.
Key ideas you can learn
- Gravity follows an inverse-square law: double the distance, a quarter of the force.
- Launch at the circular speed for a circle; faster gives an ellipse, and past escape speed the planet leaves.
- Kepler's third law: the period squared is proportional to the semi-major axis cubed.
Where this is used in the real world
Satellite engineers, astronomers and space agencies use orbital mechanics to place GPS, weather and communication satellites and to plan missions to other planets.
Who is this simulation for?
Physics students in middle school, high school and first-year university, teachers who want a quick demonstration for the projector, and anyone revising for exams. It works well for flipped classrooms because students can explore before the lesson.
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
What is escape velocity?
The minimum speed needed to leave a body's gravity and never return. It is √2 times the circular orbital speed at that distance.
Why are orbits ellipses?
For an inverse-square force the closed orbits are ellipses with the star at one focus. A circle is the special case with eccentricity 0.
Is the Orbital Motion & Gravity Simulator 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 Orbital Motion & Gravity Simulator 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.