# Physics engine acceleration and force

I'm making a very basic physics engine for fun with no roration, just movement, and ran into a problem.

Every object in my simulation has a position vector, a velocity vector and an acceleration vector, and the movement is calculated by first adding the acceleration to the velocity and then adding the velocity to the position.

I'm calculating the force exerted in a collision with force = mass * acceleration, and the acceleration of the object it's colliding with as acceleration = mass / force. The problem I'm having is that if there's no acceleration, aka a constant velocity, my 'physics engine' detects no force and kinda just dies. I'm not a physics student nor do I have any extended knowledge of how these things work, so I'd really appreciate if someone could tell me what I'm doing wrong :)

You've written Newton's second law that $$F=ma$$. Thus, if acceleration $$a=0$$, the law tells you that there is no force. However, collision is an interesting phenomenon, in this regard. In case of collision, you do have a force imparted by the bodies on each other, for a very small instance of time. This force is called 'impulse'
$$F=dp/dt$$ , where $$p=mv$$ is the momentum.