Circular Motion & Centripetal Force
Swing a ball on a string and drag it to change the radius and speed.
Drag the ball outward or inward to change the radius. Press Cut string to see it fly off in a straight line.
About the Circular Motion & Centripetal Force
Free circular motion simulator. Drag the ball to change radius, adjust speed or angular velocity, and see velocity and centripetal acceleration vectors and force. Built for physics, the circular motion & centripetal force 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.
Swing a ball on a string and drag it to change the radius and speed. 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 Circular Motion & Centripetal Force
- Use the controls to change Angular speed ω, Ball mass, Radius. The simulation reacts instantly.
- Pick an option such as Velocity, Acceleration / force, Trail to switch modes or load an example.
- Press "Cut string", "Reset" 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
- Drag the ball outward to double the radius and watch the force change.
- Double the angular speed. By what factor does the force grow?
- Press Cut string and see the tangent path.
- Compare heavier and lighter balls.
Key ideas you can learn
- Centripetal acceleration is a = v² / r = ω² r and points to the centre.
- Centripetal force F = m v² / r. It is not a new force: it is whatever pulls the object inward.
- If the string is cut the ball flies off in a straight line along the tangent.
Where this is used in the real world
Circular motion appears in cars on bends, satellites, washing machines, roller coasters and ultra-centrifuges.
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
Why does the velocity change if the speed is constant?
Velocity is a vector. Its direction keeps changing as the ball goes around, so there is an acceleration pointing to the centre.
What happens when the string breaks?
There is no inward force any more, so the ball moves in a straight line along the direction it was going at that instant.
Is the Circular Motion & Centripetal Force 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 Circular Motion & Centripetal Force 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.