Newton's third law is commonly stated as, For every action, there is an equal and opposite reaction. What this means is that, when object A exerts a force on object B, object B exerts that same force right back on object A. An example of this is firing a bullet from a gun. When a human holding a gun fires a bullet, the gun recoils with the same force of the bullet leaving the gun. That may sound counter-intuitive, because the bullet can kill a human, but the gun's recoil does not kill the human firing the gun. That is because the gun is significantly larger than the bullet, and Newton's first law states that F = ma, or force equals mass times acceleration. In other words, if the gun is 50 times larger than the bullet, then the same force will only make it accelerate to 1/50 the speed. We will be modifying our spaceship so that, whenever it shoots a projectile, it accelerates in the opposite direction of the shot based on the relative masses of the spaceship and the projectile. This will give our ship's cannon a recoil.