The Force SOP adds force attributes to the input metaball field that is used by either Particle SOP or Spring SOP as attractor or repulsion force fields. In general, force values greater than 0 cause points to be attracted, less than 0 cause points to be repelled.
/doradial - When checked, triggers a force towards or away from the centre of the metaball field, depending on the value of the force.
/radial - When Radial Force is checked, this controls the strength of the Radial Force field.
/doaxis - When checked, enables all parameters below to allow control of specific force attributes.
/dirx /diry /dirz - When Directional Force is checked, determines the direction vector axis, and activates forces along the directional vector for the directional forces below.
/axial - When Directional Force is checked, controls the force along the primary axis. Increasing this value will cause the particles to move up the primary axis of the metaball field as defined by the direction vector.
/vortex - When Directional Force is checked, this field controls the amount of twist particles are given around the primary axis. Positive values cause the particles to spin clockwise, negative values cause counter-clockwise spins. It is a centrifugal force.
/spiral - Controls the attraction/repulsion force perpendicular to the primary axis (Direction field). Values greater than 0 will cause the points to be drawn toward the primary axis. Values less than 0 push particles away perpendicular to the primary axis. It is a tangential force.
Inputs / Geometry Types
This SOP accepts only metaball-type geometry. These can be generated by a Metaball SOP or in the Model Editor. Input of non-metaball geometry has no effect.
Adjust the weights of the metaball inputs to increase or decrease the field effect within the metaball field of influence.
In general, it is a good idea to try and keep the scale of forces and force fields to a smaller rather than a larger scale. This tends to make particle movement and attraction more manageable and realistic.