Label the first body on the left Ground and the bodies that move as: One, Two and Three so that the gap between One and Two is measured as A and the point P is on body Three. nI suggest you put a translational joint between One and Two and add a Joint Load. The joint load can be a Displacement function of time that ramps the displacement of 0.1 m over some time interval. A linear ramp is the simplest way to change the distance between the bodies. An S-shaped displacement-time curve would be a more natural way to increase the displacement.n