Newton's third law explains recoil. What is the backward motion of a gun called? Recoil is the rearward motion produced when a gun is fired.
When the propellant launches a bullet and expanding gases forward, the gun receives an equal and opposite impulse. This follows from conservation of momentum: the forward momentum of the projectile and gases is balanced by the gun's backward momentum.
Recoil is often called “kick,” “kickback,” or “knockback” in everyday speech, but “recoil” is the standard technical term and the single best quiz answer. The amount depends on projectile mass and velocity, propellant gases, and the firearm's mass. A heavier gun generally moves backward more slowly for the same recoil momentum.
Recoil-management systems spread the stopping force over more time. Shooters absorb it with their body, while mounted guns may use springs, hydraulic buffers, muzzle brakes, or other devices. Muzzle rise is related but not identical: it is the gun's rotational motion caused by recoil acting below the barrel's line.