Knockdown
A physics sandbox in AR: a tap on the floor places a tower of fifteen bricks, a tap throws a ball at it, and you count what has been knocked down.
- Status
- Running
- Type
- Sandbox
- Platforms
- Mobile
- Capabilities
- Physics
- Technology
- 8th Wall · A-Frame · cannon-es
- Updated
- 11 September 2026
What it is
Knockdown is a physics demo in augmented reality: a tower appears on the floor of your real room, and you knock it down with a throw. What interested me here was not the game but the chain “SLAM surface → physical world → hit count”.
How to play
- Tap the floor — places a tower of fifteen bricks (five levels, each brick about nine centimetres).
- Tap anywhere — throws a ball there: it flies from the tap point at roughly seven metres per second.
- Reset — sets the tower up again.
What is inside
A brick counts as knocked down if it has moved more than eight centimetres from its place or tilted more than roughly forty-four degrees — the counter at the bottom shows “Down N / 15”. The physics runs on cannon-es: the ball is a body thrown at the tap point rather than “at the centre of the tower”, so the trajectory and the spin affect the result. The breakdown lives in src/physics-world.js, src/tower.js and src/knockdown.js.
Stack
- 8th Wall (SLAM, surfaces)
- A-Frame (scene and HUD)
- cannon-es (physics)