Calculating Diffusion Speed from Gas to Vacuum: How Do You Do It?

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Discussion Overview

The discussion revolves around calculating the diffusion speed of gas into a vacuum, particularly in the context of a bullet moving through a bulk of gas with a specified density. Participants explore the theoretical underpinnings and implications of diffusion in this scenario.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant suggests starting with Fick's Law as a foundation for understanding diffusion speed.
  • Several participants seek clarification on the definition of diffusion speed, indicating a need for conceptual understanding.
  • A later post introduces a specific case involving a bullet moving through gas and asks how to calculate the density evolution over time within the channel created by the bullet.

Areas of Agreement / Disagreement

Participants express uncertainty about the definition of diffusion speed and how it applies to the specific scenario presented. There is no consensus on the approach to calculating the density evolution after the bullet passes through the gas.

Contextual Notes

Participants have not yet established the assumptions or definitions necessary for a complete analysis, and the discussion includes unresolved questions about the mathematical treatment of the problem.

zhaoxh
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Hi everyone,
I'd like to ask you a question. How to calculate the diffusion speed from a bulk of gas with density of n to vacuum? Thank you!
 
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I would start with Fick's Law.
 
What is diffusion speed?
 
Dickfore said:
What is diffusion speed?


actually, I want to consider the follow case. Consider that a bullet crosses a bulk of gas (desity=n), how to calculate the density evolution (with time) within the channel after the bullet goes through the gas.
 

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