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Overview

A force is a piece of information you can attach to objects (all objects in the scene, or individual objects) that says, for example, "this object is affected by a wind" or "this object’s motion is slowed by drag". Each solver then adds that force into its calculations when it simulations the motion of dynamic objects.

Practically all forces are supported by all solvers, so you can apply forces broadly to all objects in a simulation, regardless of whether they're rigid bodies, grid-based fluids, particle fluids, cloth, or any other simulation type.

Force types

Gravity

A constant downward (-Y) pull on the affected objects per second. This is essentially identical to the uniform force. Most tools that create RBD networks add this node automatically. You can bypass the node to turn gravity off.

Drag

Adds a drag on velocities. Without drag, most solvers and forces are "frictionless" and will (unrealistically) continue forever.

When you start adding a number of other forces or strong forces, you usually want a drag to dampen extreme velocities.

Uniform

Adds a uniform amount of velocity to the affected objects every second.

Fan

Adds a certain amount of velocity to the affected objects, with the amount scaled down the further the object is from the fan.

Fluid force

Deforms cloth and wires using the motion of a grid-based or particle fluid.

Wind |

Magnet force

Bugl.

Vortex force

Votexy.

Impulse force

(Not on the shelf)

Pushes objects by a certain amount in a certain direction each second.

Field force

(Not on the shelf)

Pushes objects according to the velocity vectors in a piece of Geometry data. You attach the SOP geometry (for example, imported using a SOP Geometry node) to the Field force node’s green (data) input.

If you attach point geometry, it will use the v (velocity) attribute on the points (you can choose a custom attribute instead). If you attach a vector field it will use the field’s vectors. If you attach a scalar field (one value per voxel), it will use the gradient of the field to calculate the vectors.

Wiring forces to objects

TBD.

Adding noise to a force

Tips

  • Forces start working at the second time step (that is, frame 2 if you are not sub-stepping).

Dynamics

Learning dynamics

Colliding objects

Simulation types

Vellum

Non-DOP simulations

Next steps