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Re: [Phys-L] [**External**] Re: conserved momentum thru gas...

Interesting question. And it gave me an idea for a Fermi question: what is
the moment of inertia of our atmosphere (with respect to an axis through
the earth's center)? I know I would need Google to get started with this.

On Sun, Dec 18, 2022 at 8:45 AM Prof. Keith S. Taber via Phys-l <
phys-l@mail.phys-l.org> wrote:

Dear Omar

I would think to get a consistent answer you would have to adopt a
single frame of reference. The frame of reference you have chosen
appears to be one where you are moving around the sun on the earth's
orbit, but are not rotating with reference to the distant stars (so you
consider the earth to be a body rotating in space).

Perhaps you could turn the question round, and suggest why the
atmosphere would do anything other than (in gross terms) rotate with the
earth. Given that the atmosphere is rotating (initial condition): It is
subject to gravitational force that provides the centripetal force. What
would stop it rotating? If you treat the atmosphere as a discrete
object, it has a moment of inertia. So, what source of torque could be
applied to change its angular momentum?

Keith

On 18/12/2022 12:56, O A via Phys-l wrote:
Thank you for the response.

To try and be more clear:

how is the atmosphere keeping up with the rotational velocity of the
spinning earth? This would neccesarily mean the same angular velocity
but a
greater linear velocity at, say 100km above solid earth. Again though,
that's assuming the earth/atmosphere 'system' is 1 frame of reference
(not
2 separate).

My goto was gravity as well, but this answer had some weaknesses (to me),
so: I asked here : )

-Omar

On Sun., Dec. 18, 2022, 7:45 a.m. Prof. Keith S. Taber via Phys-l, <
phys-l@mail.phys-l.org> wrote:

On 17/12/2022 21:42, O A via Phys-l wrote:
How is conservation of momentum 'transferring' through scores of miles
of
gas?
Not sure I fully understand the question, but the molecules collide,
which does not change the total momentum. Yet, there is another factor
to consider. Gravity. This provides the centripetal force acting on the
molecules so that there is an interaction to transfer momentum and
change their velocity.

Is that what you were thinking?

Keith

--

“…if intelligent means quick to learn, perhaps it also means receptive
and hence too credulous?”
<https://science-education-research.com/commonplace/>

Dr. Keith S. Taber

Emeritus Professor of Science Education
University of Cambridge
http://www.educ.cam.ac.uk/staff/taber.html

Senior Member
Homerton College, Cambridge

https://science-education-research.com

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