recoil

thumb|250px|An early naval cannon, which is allowed to roll backwards slightly when fired, and therefore must be tethered with strong ropes

Recoil (often called knockback, kickback or simply kick) is the rearward thrust generated when a gun is being discharged. In technical terms, the recoil is a result of conservation of momentum, for according to Newton's third law the force required to accelerate something will evoke an equal but opposite reactional force, which means the forward momentum gained by the projectile and exhaust gases (ejectae) will be mathematically balanced out by an equal and opposite impulse exerted back upon the gun.