Bullet Acceleration in Vacuum: Why Does It Stop After Exit?

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Discussion Overview

The discussion centers on the behavior of a bullet fired in a vacuum, specifically addressing why it stops accelerating upon exiting the muzzle despite having an initial velocity. The scope includes conceptual understanding of forces and motion in a vacuum, as well as the mechanics of bullet acceleration within a gun barrel.

Discussion Character

  • Conceptual clarification, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions why the bullet stops accelerating after exiting the muzzle, suggesting that it exits with some force that should contribute to its velocity.
  • Another participant explains that the combustion gases inside the barrel exert a force on the bullet, leading to acceleration, but once the bullet exits, the gases disperse, and no further force acts on the bullet, resulting in constant velocity.
  • A third participant succinctly states that outside the muzzle, there is no force acting on the bullet, leading to zero acceleration.
  • A later reply reflects on the concept of acceleration, noting that many might confuse the bullet's behavior with that of a thrown stone, which accelerates to a velocity before decelerating, yet acknowledges the explanation provided.

Areas of Agreement / Disagreement

Participants generally agree on the mechanics of bullet acceleration and the role of forces inside and outside the barrel, but some confusion remains regarding the initial conditions and perceptions of motion after exiting the muzzle.

Contextual Notes

The discussion does not resolve the potential misconceptions about acceleration and velocity in different contexts, such as comparing the bullet's motion to that of a thrown stone.

Who May Find This Useful

This discussion may be of interest to those exploring concepts of motion, forces in a vacuum, and the mechanics of firearms.

rajeshmarndi
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If a bullet is fired from a gun in vacuum(assume no gravity, no resistance).

why is it that the bullet accelerates 0 to v inside the barrel but as it exit the muzzle it stop accelerating.

Isn't when the bullet exit , it exit with some force which give it a initial velocity v.
 
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As combustion gases inside the barrel expand they exert a force on the bullet, as long as the force is applied the bullet accelerates. When the bullet exits the muzzle the combustion gases can escape and will disperse in the vacuum.
Because the gas can no longer exert a force on the bullet it stops accelerating and maintains a constant velocity. It does not keep some of the force that initially accelerated it.
 
out of the muzzle, there is no force putting on the bullet --> a = 0
 
It seems a bit difficult as the last force available to the bullet as it exit, will not provide acceleration.

Because many will think that when a stone is thrown it will accelerates to some velocity and then deaccelerate.

But that's right. Thanks for the answer.
 

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