Forces & interaction

This one is interactive: click any shape to launch it. Under the hood it ray-picks the body under your cursor and applies an impulse at the exact contact point, so an off-center hit adds spin. Drag empty space to orbit the camera.

Click a shape to launch it · drag to orbit

❚❚ Pause ↺ Reset

Run demo

Loading physics…

How it works

Picking uses the same castRay from the raycast example: unproject the cursor to a world-space ray, cast it, and apply an impulse to whatever it hits.

canvas.addEventListener("pointerdown", (event) => {
  const ray = cursorToWorldRay(event, camera); // { origin, direction }
  const hit = world.castRay(ray.origin, ray.direction);
  if (!hit?.body) return;

  // Impulse = instantaneous change in momentum. Applying it at hit.point
  // (off-center) also imparts spin.
  hit.body.applyImpulse([0, hit.body.mass() * 8, 0], [hit.point.x, hit.point.y, hit.point.z]);
});

Ways to move a body

Method	Use it for
applyImpulse(v, point?)	An instant kick — jumps, hits, explosions.
addForce(v, opts?, point?)	A continuous push, applied until the next step (thrusters, wind).
addTorque(v) / applyAngularImpulse(v)	Rotational push.
setLinearVelocity(x, y, z)	Set velocity directly.

Related

• Bodies & motion · Raycasting