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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. You can find shelf tools for most forces on the Drive Simulation tab.

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

Applies forces to resist the current motion of objects relative to a turbulent wind

Magnet force

Apply forces on objects using a force field defined by metaballs.

Vortex force

Applies a vortex-like force on objects, causing them to orbit about an axis along a circular path.

Impulse force

Pushes objects by a certain amount in a certain direction each second. This node does not have a shelf tool, but can be found in the tab menu.

Field force

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. This node does not have a shelf tool, but can be found in the tab menu.

Tips

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

  • Use Noise field to add noise to a force.

Dynamics

Learning dynamics

Colliding objects

Simulation types

Non-DOP simulations

Next steps