Gravity on air molecule vs. diffusion into vacuum

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Discussion Overview

The discussion revolves around the forces acting on the Earth's atmosphere, specifically the role of gravity in retaining air molecules and the opposing effect of diffusion into the vacuum of space. Participants explore the conceptual and physical implications of these forces, seeking to understand the mechanics behind atmospheric retention.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Exploratory

Main Points Raised

  • Some participants assert that gravity is the sole force keeping the atmosphere enveloped around the Earth.
  • Others argue that diffusion, while not a force in itself, acts as a consequence of the pressure gradient opposing the gravitational force.
  • A participant seeks a proof that is self-evident and not overly complex mathematically, indicating a desire for a more intuitive understanding.
  • Another participant questions the specific proof being sought, prompting further clarification on the nature of the inquiry.
  • One participant reflects on their past experiences in a vacuum chamber lab, suggesting that the engineering challenges of maintaining a vacuum relate to the physics of atmospheric retention.
  • There is an expressed curiosity about the physics preventing air from leaking out of the Earth, paralleling the issues faced in vacuum chambers.

Areas of Agreement / Disagreement

Participants generally agree that gravity plays a crucial role in retaining the atmosphere, but there is contention regarding the characterization of diffusion and its implications. The discussion remains unresolved regarding the specific mechanics and proofs related to these forces.

Contextual Notes

Participants have not reached a consensus on the definitions and roles of diffusion versus gravitational forces, and there are unresolved questions about the nature of the proof being sought.

houlahound
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OK the atmosphere by definition envelopes the earth.The force keeping it here is solely gravity.

The "force" opposing this is diffusion across a pressure gradient into the vacuum of space.

Assuming that is correct how could I prove this other than looking out the window.

Newton's law of gravity will give the force Earth exerts on a single molecule, the force of the vacuum??
 
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The force keeping it here is solely gravity. yes

The "force" opposing this is diffusion across a pressure gradient into the vacuum of space.
Diffusion isn't really a force; it's more the consequence of a force. But I understand what you mean.

What kind of proof did you have in mind ? A derivation of the http://acmg.seas.harvard.edu/people/faculty/djj/book/bookchap2.html probably isn't what you mean, or is it ?

[edit] made a quote of the quote
 
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A proof that is self evident and not too hard-core in the math.
 
But what is it you want to prove ?
 
That the Earth's atmosphere sticks to the earth.

Other than just breathing the proof.

The question is motivated by many, many...many years ago as an undergrad I used to hang out in the postgrad e2e collision lab and saw the engineering involved to keep in gassing of the atmosphere screwing up the low vacuum chambers enclosing the experiments.

I figure if air can leak into those elaborate chambers to be such a measurable problem then what's the physics stopping same air leaking out of the wall-less chamber of the earth.

I get we exist therefore we have an atmosphere, I just want to get the physics of the opposing "forces".
 
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