xpPhysical General tab menu.
Checking this box enables the xpPhysical modifier.
Set at Independent by default.
You can change this to Action-Controlled.
In this mode, particles will be affected if they come into the field of effect of the modifier.
When in the Action-Controlled Mode setting, the modifier will only act on a particle when told to do so by an action.
This setting controls how often the parameters will change.
By default it is set to change every frame, but this can be increased to slow down the rate of change, if desired.