# Recoil

As Rebound is called the backlash that occurs when a mass accelerates is. The direction of recoil is opposite to the direction of acceleration .

With recoil, a distinction can be made between recoil impulse , recoil speed , recoil energy and recoil force.

## Recoil from firearms

The recoil from firearms is a factor in indoor ballistics .

According to the principle of conservation of momentum, the recoil momentum is equal to the momentum imparted to the projectile and the forward-flowing gases of the propellant charge . The projectile momentum is the product of the mass and the muzzle velocity of the projectile: ${\ displaystyle p _ {\ mathrm {R}}}$${\ displaystyle m _ {\ mathrm {G}}}$${\ displaystyle v_ {0}}$

${\ displaystyle p _ {\ mathrm {R}} = m _ {\ mathrm {G}} \ cdot v_ {0}}$

The exact proportion of propellant gases in the total pulse is difficult to calculate and is generally determined experimentally. For practical (approximate) calculations, half the mass of the propellant charge is added to the projectile mass.

The speed of the recoil movement of the weapon results from the mass of the projectile , from the speed of the projectile and from the ratio of the weapon mass to the projectile mass according to the principle of conservation of momentum : ${\ displaystyle v _ {\ mathrm {R}}}$${\ displaystyle m _ {\ mathrm {G}}}$${\ displaystyle v_ {0}}$${\ displaystyle m _ {\ mathrm {W}}}$

${\ displaystyle v _ {\ mathrm {R}} = {\ frac {m _ {\ mathrm {G}} \ cdot v_ {0}} {m _ {\ mathrm {W}}}}}$
Possible effect of recoil, location Musée Militaire Vaudois, Morges , Switzerland
Recoil principle of a firearm

The energy of the recoil results from the kinetic energy of the projectile, the kinetic energy of the gases expanding forward or flowing out of the muzzle and the ratio of the mass of these components to the mass of the weapon.

The energy of the recoil can be calculated from the recoil speed: ${\ displaystyle W _ {\ mathrm {R}}}$

${\ displaystyle W _ {\ mathrm {R}} = {\ frac {m _ {\ mathrm {W}} \ cdot v _ {\ mathrm {R}} ^ {2}} {2}}}$

This means that a light projectile that leaves the barrel with the same muzzle energy as a heavier projectile emits less recoil energy than the heavy projectile, provided the weapon mass is the same. Especially with strong charges that are fired from relatively short barrels, the recoil effect of the gases flowing out of the barrel muzzle can contribute a significant proportion to the total energy of the recoil (rocket effect).

The recoil force corresponds to the force of acceleration to which the projectile and the forward-flowing gases are exposed. The acceleration force is the product of the projectile mass and the projectile acceleration : ${\ displaystyle F _ {\ mathrm {R}}}$${\ displaystyle F _ {\ mathrm {B}}}$${\ displaystyle m _ {\ mathrm {G}}}$${\ displaystyle a}$

${\ displaystyle F _ {\ mathrm {R}} = F _ {\ mathrm {B}} = m _ {\ mathrm {G}} \ cdot a}$

The bullet acceleration can ideally be calculated from the muzzle velocity of the bullet and the barrel length of the weapon : ${\ displaystyle v_ {0}}$${\ displaystyle s}$

${\ displaystyle a = {\ frac {v_ {0} ^ {2}} {2 \ cdot s}}}$

The recoil force is transferred to the weapon by the high pressure gases of the propellant charge. This force only acts on the weapon for the short period of time it is fired, whereby in practice the course of the recoil force depends on the course of the gas pressure after the ignition of the propellant charge.

The recoil of weapons can e.g. B. be lowered by muzzle brakes . In addition to muzzle brakes, the recoil of modern guns is usually also absorbed by a hydraulically braked barrel return . In order to be able to almost entirely avoid the undesirable effects of recoil, recoilless guns were also developed.

The energy of recoil is at recoil loaders used to open the shutter after a shot to eject the empty shell casing and to track a new cartridge into the cartridge chamber.

## Recoil as a means of propulsion

The recoil of a jet of water lifts a flyboard into the air

In jet propulsion such as rocket engines and jet engines , the recoil force (commonly called thrust ) of a medium accelerated in a nozzle is used as the driving force. The recoil force is the product of the flow rate of the nozzle and the speed of the outflowing medium . ${\ displaystyle F _ {\ mathrm {R}}}$${\ displaystyle {\ dot {m}} _ {l}}$${\ displaystyle v}$

${\ displaystyle F _ {\ mathrm {R}} = {\ dot {m}} _ {l} \ cdot v}$

## Recoil in atomic, nuclear and particle physics

The conservation laws for momentum and energy apply to physical systems that have to be described using quantum mechanics , as well as in classical mechanics (see also kinematics ). Therefore, when emitting gamma radiation , for example, the emitted photon does not receive exactly the entire energy released by the transition, but the atomic nucleus retains a fraction of it as the kinetic energy of its recoil; see also Mössbauer effect .

The recoil protons generated by elastic collisions with fast neutrons in a hydrogen-containing material can be used for the detection and energy measurement of these neutrons (see neutron detector ).

## Recoil in running

Muscle and connective tissue are elastic. If they are stretched and then relaxed, a recoil effect occurs. When running forefoot , this can be used for energy-saving propulsion - but not when running the back of the foot . In order to optimally use the energy stored in the tissue for propulsion, the shortest possible contact time between the foot and the ground is necessary.