Physics Workshop
A small physics bench. Put things together, press Run and watch what really happens — then pause, step frame by frame and change one thing at a time.
Build small experiments from balls, boxes, ramps, pins and springs, then run, pause and step time.
FreeOn this device
Run it. Does the ball roll or slide down the ramp? Watch its spin.
| Body | Mass | Friction | Bounce | x (m) | y (m) | Speed (m/s) |
|---|---|---|---|---|---|---|
| fixed | 0.4 | 0.1 | 4.00 | 2.20 | — | |
| 1 | 0.4 | 0.3 | 1.73 | 3.69 | 0.00 | |
| 2 | 0.4 | 0.1 | 9.50 | 0.40 | 0.00 |
Motion by Planck.js, an open-source (MIT) version of the Box2D engine, at a fixed 60 steps a second. A game-quality simulation for exploring ideas — not certified engineering, and energy is not perfectly conserved. Force arrows: 1 m of arrow per 50 N.
Controls
- Choose a tool and tap the blueprint: Circle, Box and Ramp add bodies, Pin fixes a body at a point, Spring joins two points (tap one end, then the other).
- Select picks a body to move it or edit its mass, friction, bounciness, size and starting speed; the object table lists every body too.
- Run, Pause and Step (one sixtieth of a second) move time; Reset puts the scene back exactly. Undo works while editing. While running, drag a body to pull it.
The rules
- Motion comes from Planck.js, an open-source version of the Box2D engine used in many games, stepped 60 times a second.
- Masses run from 0.1 to 100 kg, friction and bounciness from 0 to 1, gravity from 0 to 20 m/s². Up to 100 bodies and 150 pins and springs.
- A pin lets a body turn about a point; a spring pulls its two ends back towards their starting distance.
Scoring, saving and limits
No score — each guided experiment asks a question to answer by watching.
Your scene and view settings are kept on this device. Running is never saved part-way; Reset always starts from the scene.
A game-quality simulation for exploring ideas — not certified engineering. Energy is not perfectly conserved, and very fast or crowded scenes can behave approximately.
Questions
- Why can't I edit while it's running?
- So Reset can always rebuild exactly what you made. Press Reset, change things, then Run again.
- What are the amber arrows?
- The force each pin or spring is applying, drawn 1 metre long per 50 newtons.
- Why does a ball roll rather than slide?
- Friction grips it and turns it. Set friction to 0 and it slides without turning.