lua.box3d.body.acceleration
body:acceleration()
body:acceleration(x,y)
body:acceleration(x,y,r)
body:acceleration(nil,nil,r)
set body acceleration, which is to say we set the body force multiplied by mass or rotational inertia. Note that this will not work on a 0 mass body, I think you have to fake a mass on a body with no shapes first.
x,y is acceleration per second applied to center mass, will be cleared if nil
r is rotational acceleration per second in radians , will be cleared if nil
This will replace force and acceleration and as force is applied then cleared during a step, this needs to be set for every step.