Collisions & Momentum Lab
Crash two carts together and compare momentum and kinetic energy before and after.
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About the Collisions & Momentum Lab
Free collision simulator. Set masses, velocities and elasticity from perfectly inelastic to perfectly elastic and see momentum and kinetic energy before and after. Built for physics, the collisions & momentum 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.
Crash two carts together and compare momentum and kinetic energy before and after. 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 Collisions & Momentum Lab
- Use the controls to change Red cart mass, Red cart velocity, Blue cart mass, Blue cart velocity, Elasticity. The simulation reacts instantly.
- Pick an option such as Sticky (inelastic), Bouncy-ish, Elastic to switch modes or load an example.
- Press "Run", "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
- Run an elastic collision with equal masses.
- Make it perfectly inelastic and read the energy lost.
- Make one cart much heavier.
- Send the carts toward each other.
Key ideas you can learn
- Total momentum is conserved in every collision without outside forces.
- Kinetic energy is conserved only in perfectly elastic collisions.
- In a perfectly inelastic collision the carts stick together and lose the most kinetic energy.
Where this is used in the real world
Momentum conservation is used in car-crash safety design, billiards, rockets and particle physics experiments.
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 the difference between elastic and inelastic collisions?
Both conserve momentum, but elastic collisions also conserve kinetic energy. Inelastic collisions turn some kinetic energy into heat, sound or deformation.
Where does the lost kinetic energy go?
Into other forms such as heat and sound, and into changing the shape of the objects.
Is the Collisions & Momentum 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 Collisions & Momentum 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.