State and explain law of conservation of linear momentum. Briefly explain recoil of gun .during firing of bullet.
Answers
The law of conservation of linear momentum states that the total momentum of a system of particles remains constant, so long as no external forces act on the system. Equivalently, one could also say that the total momentum of a closed system of particles remains constant. Here, the term closed system implies that there are no external forces acting on the system.
This holds true even if there are internal forces between particles. If a particle A exerts a force F_{BA} on a particle B, then the particle B would exert a force of F_{AB}=-F_{BA} on A. The these two forces are Newton’s third law pairs, and so they would act for the same duration of time \Delta t. The change in momentum for particle B is \Delta \vec{p_B}=F_{BA}\Delta t. For particle A, the change in momentum is \Delta \vec{p_A}=F_{AB}\Delta t=-F_{BA}\Delta t=-\Delta \vec{p_B}. The total change in momentum within the system is indeed \Delta \vec{p_B}+\left(-\Delta \vec{p_B}\right)=0.
Because of Newton’s Third Law - for each action, there is an equal and opposite reaction.
Action - the cartridge is fired. This energy acts on the bullet (expelling it from the cartridge, down the barrel, and out the muzzle).
Reaction - an equal amount of energy acts against the back of the chamber (by way of the back end of the cartridge, which is solidly seated against the back of the chamber). You FEEL less force because it’s distributed over a wider area and it’s acting on a much larger object (the firearm, which is MUCH bigger than the bullet), but it’s the same amount of energy.
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