Why does a gun not move backwards with the same speed the bullets move forward?

Answer 1

Guns do have varying degrees of "kick" when they are fired; the amount of kick depends on the weapon and the type of round being fired. In some cases the kick is substantial and training is needed to avoid injury to the shooter. But guns do have mass, so the gun's own inertia helps to dampen the kick. I think it's not only the bullets or their speed that need to be accounted for. In a sense, a gun is a special case of jet engine at the moment of firing, and all the gasses and particles ignited during the firing act like jet fuel propelling the gun backwards. By Newton's third law of motion, every force exerted by A on B is equally exerted by B on A. So the force that propels the bullet and gases forwards from the gun also propels the gun backwards. The gun does not accelerate to anything like the speed of the bullet because: * Acceleration is inversely proportional to mass, and the gun is much heavier than the bullet. * Your shoulder or hand works against the force from the explosion. Despite the fact that the gun exerts as much force against you as against the bullet, you are not injured. This is chiefy because your region of contact with the weapon is a much greater area than the wrong end of the bullet, distributing the force over a wide area.