[meteorite-list] Entry Dynamics in Peru

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu, 4 Oct 2007 17:40:01 -0500
Message-ID: <058601c806d7$858636c0$b92ee146_at_ATARIENGINE>

Hi, Mike, List,

    At Carancas the meteoroid only traveled though
58% of the Earth's atmospheric mass and density.

    "Pressure" is just the mass of the atmosphere
that is above where you are. Picture a square inch
cross-section column rising from the surface of the
planet out to the vacuum of space. The air in it
weighs 14.7 pounds if you start at sea level, or
1200 grams.

    When you climb to where the pressure is halved,
so is the mass of air above you and the mass of the
air below you is the same as the amount above you.
This happens at 5486 meters or 18,000 feet.

    At 8376 meters, or 27,480 feet, one-third of the
atmosphere is above you and two-thirds below,
and you are still not at the summit of Everest. But,
oxygen partial pressure is down to less than 1 lb.,
and you are seriously short. (Pilots are recommended
to go on Ox at 15,000 feet just to be sure they don't
get whacky. Or is it required?)

    For all practical purposes, as a biological entity,
you're "in space" at 23,000 feet, for this is the absolute
limit of long-term survival without breathing aparatus,
with 1.3 lbs of oxygen partial pressure.
 
    At 16,132 meters, or 52,926 feet, 90% of the air
is below you and in another 10,000 feet, there's danger
your blood will begin to boil lightly in the warmest parts
of your body. At 30,901 meters, or 101,381 feet, 99% of
the atmosphere is below you. If you're flying something
with wings, they are totally useless.

    You'll notice pressure falls off quickly, exponentially
actually, as a power of "e" or would if the atmosphere
were the same temperature at all altitudes, but the cold
upper atmosphere is heavier than the formula says...

    The formula is:

Pressure at altitude A meters =
Pressure at sea level X "e" ^ ( - ( A / 8500 ) )

    (Sea level pressure is 14.7 lbs. per sq. in., or
1.2 kg. per sq. meter. 8500 meters is the "scale
height" where pressure goes down to 1/e. And
"e" goes on forever like "pi."
2.71828182845904523536028747135266249775
7247093699959574966967627724076630353547
5945713821785251664274274663919320030599
218174135966290435729003342952605956307...

    I just use 2.72, OK? You can use the formula to
get a rough idea of the oxygen percentage at the
top of any mountain of known height, instead of
just flopping down unconscious when you get there.

    You can also use it to calculate the density of air
at any altitude, since pressure and density are just two
ways of counting the number of molecules in a cube
of air.

    More than you ever wanted to know, right?


Sterling K. Webb
--------------------------------------------------------------
----- Original Message -----
From: "Mike Fowler" <mqfowler at mac.com>
To: <meteorite-list at meteoritecentral.com>
Cc: "Mike Fowler" <mqfowler at mac.com>
Sent: Thursday, October 04, 2007 3:53 PM
Subject: [meteorite-list] Entry Dynamics in Peru


> As to the mention of dense atmosphere, doesn't 90% of
> the mass of the atmosphere lie below 2.5 miles above
> sea level?

 From my mountain climbing days, I remember that the rule of thumb
was that 50% of the atmosphere was below 3.5 miles or 18,000 feet.

The highest I made was the summit of Popocatepetl in Mexico, 17,800
feet above sea level.

Mike Fowler
Chicago
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Received on Thu 04 Oct 2007 06:40:01 PM PDT