[meteorite-list] Velocity a meteorite hits the ground?

From: Piper R.W. Hollier <piper_at_meteoritecentral.com>
Date: Thu, 09 Apr 2009 12:39:00 +0200
Message-ID: <200904091039.n39AdM5j000576_at_smtp-vbr1.xs4all.nl>

Hello Aubrey and list,

There is a good basic explanation of terminal velocity here:

http://en.wikipedia.org/w/index.php?title=Terminal_velocity

A Java applet for do-it-yourself calculations can be downloaded here:

http://www.grc.nasa.gov/WWW/K-12/airplane/termv.html

A table with calculated free fall velocities for hailstones (assuming
a spherical form) can be found here:

http://hyperphysics.phy-astr.gsu.edu/Hbase/airfri2.html#c4

Real hailstones are not spherical and may not be solid ice, so "your
results may vary," but the terminal velocities given are:

1.0 cm radius (2 cm dia.): 69.5 km/hr, 19.3 m/s, 43.2 mph
2.0 cm radius (4 cm dia.): 98.3 km/hr, 27.3 m/s, 61 mph

We can probably safely estimate that hailstones in the 3.0 to 3.5 cm
range will come out somewhere in between these two values. One
complicating factor is that the thunderstorms that produce hailstones
can have very powerful downdrafts (10 m/s or more, if I am not mistaken).

All other factors being equal, the terminal velocity is proportional
to the square root of the density of the material, so we can
calculate how much faster a similarly sized meteorite would fall.
Assuming a density of about 0.9 gm/cm3 for hailstones and 3.5 gm/cm3
for ordinary chondrites (ignoring porosity effects in both cases), a
typical stony meteorite (or is it still a "meteoroid" until it
reaches the ground?) should free fall about twice as fast as a
hailstone of a similar size. A useful discussion of stony meteorite
density can be found here:
http://homepage.mac.com/brother_guy/.Public/Meteorite%20Densities.pdf

Assuming a typical density of iron meteorites of about 7.8 gm/cm3
(depends on proportions of nickel and of non-metallic minerals), the
terminal free fall velocity of an iron meteorite upon reaching the
ground should be about three times that of a hailstone.

Best wishes to all,

Piper

At 07:23 09-04-09, you wrote:
>Hi
>
>I'm sure this is a very simple question. The other day I was caught in
>a hail storm and was hit by 30-35mm diameter hail stones. One hit my
>exposed hand and made a nasty bruise. At what speed were these hail
>stones falling? By comparison, at roughly what speed do meteorites
>fall assuming they have lost all of their cosmic velocity. I am
>assuming it will be a little faster as meteorites are heavier and so
>the drag will have less of an effect.
>
>Thanks, Aubrey
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Received on Thu 09 Apr 2009 06:39:00 AM PDT