Simulation
One physics world drives every simulation type: particles, cloth, hair, soft and rigid bodies, fluid and smoke.
Every kind of simulation lives in the same world and is solved together. A cloth flag, a pile of rigid blocks, a hair groom and a puff of smoke interact in one scene without a bridge between systems.
One solver, many behaviours
A single solver runs on the GPU. What makes a piece of geometry behave like cloth rather than a rigid body or hair is which rules are applied to it: the forces, and the connections between its points.
Choose a behaviour by choosing a node.
Particle Sim for points that fly, fall or pile up: sparks, dust, sand, snow.
Cloth Sim for flags, banners and capes on a mesh.
simulation.hair for strands and grooms.
Soft Body Sim for meshes that squash and hold their volume.
Rigid Body Sim for solid objects that collide and stack.
All of these feed a Physics World, the coordinator node that gathers bodies, colliders, forces and joints and runs the simulation. Raw geometry wired straight into Physics World, a Points node for instance, is treated as a rigid body with no further setup.
Because every sim type shares one world, they collide with and push on each other with no bridge node. Drop rigid bodies onto a cloth sheet and both react.
Playback drives the solver
A simulation advances in time only while playback is running, unlike most nodes, which recompute as soon as something changes.
Play advances time and steps the solver frame by frame. This is the only way a sim accumulates motion. Pause freezes the world where it is: you can still inspect the frame, tweak nodes and move around, but bodies hold their pose and do not settle, fall or drift. Bursts and one-shot events are held too, so a pile stops settling and a fountain stops spraying.
Cloth hanging stiff with nothing moving is almost always playback that is not running.
Resetting
Rewind to start fresh. Scrubbing the timeline back to the start re-runs the simulation from the beginning, so frame 1 always looks the way it did the first time and the same settings give the same motion. Change a parameter, jump back to the start, watch it play out again.
Scrubbing backwards into the middle of a sim re-runs everything from the start to reach that frame, which takes time on heavy scenes. Let long or expensive simulations play forward rather than scrubbing around them.
Forces, colliders and constraints
Gravity, wind, attractors, vortices, turbulence and drag come from Force Field, covered in Forces & collisions. Colliders are static shapes the simulation cannot pass through, including Distance Fields; a Volume wired in as a collider becomes a solid boundary. Joints pin bodies together, hinge them or weld them, covered in Joints & constraints.
Raycasts, overlaps and triggers against the world are in Queries (sim-free).