Rigid bodies

Solid objects that tumble, bounce and stack: boxes on a floor, dice in a cup, a cascade of crates.

A rigid body keeps its shape whatever hits it. The Rigid Body Sim node runs the whole stack on the GPU, so a crowd of objects stays real-time.

Getting things falling

Feed geometry into Rigid Body Sim and wire it into the scene, or drop the shapes into a Physics World and give it a ground. Each separate piece of geometry becomes its own solid body. Add a floor, either a Physics Collider or the built-in ground, and press play. Plain geometry sent into the physics world becomes a rigid body with no flag to set.

The pose of each body, where it ends up and how it is rotated, is written back onto the shapes as they tumble, so the original look survives.

The three controls that matter

Most of the feel of a rigid sim comes from three properties.

Mass is how heavy a body is. Heavier bodies shove lighter ones aside and are harder to push around. Friction is how much surfaces grip: high friction makes objects slow and stack cleanly, low friction lets them slide like ice. Restitution, or bounciness, is how much energy survives an impact, from a dead thud at zero to a lively bounce at high values.

A pile of bricks needs high friction and low bounce. A handful of rubber balls needs the opposite.

The physics world

Bodies live in a shared world that also holds the floor, walls, gravity and any forces. Everything wired into the same Physics World collides with everything else and obeys the same gravity.

• Colliders, static surfaces to land on and bump into: floor, ramps, walls.

• Gravity, the world's downward pull. Turn it down for a floaty, slow-motion feel.

• Forces from a Force Field: wind, vortexes and attractors push bodies around as they move.

Pin bodies together with joints to build hinges, chains and ragdolls. See Joints & constraints.

Collisions and contacts

Bodies collide with each other, with static colliders, and with Distance Field shapes used as collision boundaries. Anti-tunnelling is always on, so a fast-moving object will not shoot through a thin floor. There is no switch to enable it.

To react when things touch, spawning particles, changing a colour, firing a sound, use a Trigger to catch the moment two bodies meet.

Parameters

See also

• Joints & constraints

• Forces & collisions

• Queries (sim-free)

• Time & playback