[meteorite-list] Archive: (meteorobs) Meteoroid heating: Ram pressure, friction or both?

From: David Weir <dgweir_at_meteoritecentral.com>
Date: Thu Apr 22 10:06:13 2004
Message-ID: <3DC273CF.84E45CF0_at_earthlink.net>

Hello all,

I saved a great post to the list by Russ K. that addressed this issue a
couple of years ago:
___________________________________________

Compression is correct - but - compression is motion,
motion produces friction and thus heat. And, you are
right -- it's not just semantics. It identifies a process
making it a wonderful teaching model.

As the air (gas) molecules are compressed, they move.
Any "gas" that suddenly has to move (compression) has
more and more molecules banging into each other - heat
from friction.

The causal relationship is:

Compression/motion
Motion/friction
Friction/heat

What happens afterwards is a complex process called
gas dynamic drag which deals with the thermal effects of
gas in motion. Ultimately the resultant heat is partitioned
away from the meteoroid through ablation.

There have been several papers in "Meteoritics" over the
years addressing this process. I can look up some references
if you like.

Russ K.
New England Meteoritical

www.meteorlab.com
_____________________________________________

Robert Verish wrote:
>
> In that page, Phil states, "In reality, it isn't
> friction, but *ram pressure* that heats meteoroids.
> When a gas is compressed it gets hot, like when a
> bicycle pump is vigorously used to inflate a tire.
> A meteoroid, moving at 33,500 mph (15 kilometers a
> second) or more compresses the air in front of it
> violently. The air itself gets very hot, which is
> what heats the meteoroid. That's fact, not friction."
>
> What a fine pun! :) But on to that QUESTION: I can
> recall reading in Oepik's "Physics of Meteor Flight
> in the Atmosphere", that the formation of a pocket
> of compressed air under a meteoroid critically de-
> pends on the SIZE (cross-section) of that particle:
> below a certain cross-section, the particle would
> in fact (per Professor O) NOT create it's own "air
> shield", and so would be directly impacted by air
> molecules throughout it's flight... And of course,
> we can assume that particles which are JUST large
> enough to form air shields, might still experience
> occasional but significant direct molecule impacts.
>
> So the question is, Which is really more important
> for the average *visible* meteor: the ram pressure
> Phil describes so well, or direct impact friction?
Received on Fri 01 Nov 2002 07:30:07 AM PST