I'm new to physics, so I'm sure the explanation is very simple, but I cannot wrap my head around Newton's 2nd law F=ma. It is very easy to understand until I plug 0 into a. Wouldn't this make the force of the reaction disappear? For instance if a 100kg rock traveling east at constant velocity of 25m/s2 hits a 20kg rock traveling west at constant velocity of 25m/s2 at the point of impact neither object is accelerating (due to constant velocities). Wouldn't the total acceleration be 0 and nullify the force? Where am I going wrong? What am I forgetting? Thank you!