Kinetic theory of gases momentum

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Discussion Overview

The discussion revolves around the kinetic theory of gases, specifically focusing on the momentum of particles when they collide elastically with a wall. Participants explore the mathematical representation of momentum changes during such collisions.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant presents a formula for momentum and questions the appearance of a second negative sign in the momentum change calculation.
  • Another participant explains that when a particle bounces elastically off a wall, its velocity and momentum change direction, which may clarify the situation.
  • A participant acknowledges understanding that the second negative sign arises after the particle has impacted the wall, leading to a total momentum change of 2mvx.
  • One participant concludes that the relationship mvi = -mvf leads to the expression for momentum change as -2mvx.

Areas of Agreement / Disagreement

Participants appear to reach an understanding regarding the mechanics of momentum change during elastic collisions, but the discussion does not indicate a consensus on the initial question about the second negative sign.

Contextual Notes

There may be limitations in the assumptions regarding the definitions of momentum and the conditions of elastic collisions that are not fully explored in the discussion.

lukasz08
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p=momentum=(mass*volume)

delta px = pf - pi
mvf - mvi
mvx - (-mvx) <<<<---- where does this second negative come from ? what am i missing here?
2mvx


in my book it shows that
delta px = - mvx - (mvx) = -2mvx
 
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When a particle bounces elastically off a wall, its velocity (and momentum) changes direction. Does that help?
 
yes i understand that so the second negative appears after the particle has hit the wall resulting in the 2mvx ?
 
ok i got it mvi = -mvf therefore -mvi - mvf = -2mvx
 

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