I am trying to set a force equal to gravity... however I am not having much success. For a particular entity, I want to exert a force equal to gravity in order to maintain its .z, but so that it can still be acted upon in a collision.

i've tried setting a force to (0,0,(obj_mass*-1*grav) because f(grav)=mg and the new vector must oppose gravity. However, this does not work for me. What am I missing?