Nope, still repulsive forces. Think about it - two balls head towards each other, collide, and move away from each other, having experienced a repulsive force.

Nope, still repulsive forces. Think about it - two balls head towards each other, collide, and move away from each other, having experienced a repulsive force. Reverse time, and it looks exactly the same. Or more mathematically, force is measured in Newtons, which is kg * m / s / s. Reverse the sign of the seconds part of that, and, oh, it's squared so it ends up being exactly the same.