Strewn field shape is the product of two factors: (1) the meteoroid may
break up over a long distance, and (2) individual components are
distributed by wind during cold fall. In the first case, this breakup
may cover a lot of ground, but happens while the meteoroid is still
hypersonic. So no more than a few seconds separate the beginning and end
of the breakup. After that, everything is falling at the same rate, so
(in the absence of aerodynamic effects) will land at about the same
time. In the second case, wind only affects the horizontal velocity
component, so it has no effect on the landing time.
The only significant factor is the timing introduced by the terminal
velocities of the individual components. Given a reasonable range of
shapes and sizes, you might have some components falling at 50 m/s, and
others at 200 m/s. For a typical fall height, that means you could
reasonably expect as much as 5-10 minutes between the first and last
components reaching the ground.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
----- Original Message -----
From: "Robert Woolard" <[EMAIL PROTECTED]>
To: <meteorite-list@meteoritecentral.com>
Sent: Wednesday, March 19, 2008 8:40 AM
Subject: [meteorite-list] Impact Duration Time
Hello List,
Would any members be able to help with a question I
have regarding the "impact-duration-time" (???) of
some typical falls? I don't know if that's the best
terminology to use, but what I mean is: What would be
a "typical" measure of time between the impact of the
FIRST (known) individual at the start of the
strewnfield, and the fall of the LAST (known)
individual? I can't remember ever having read of any
instances where these times were actually determined.
I know the odds for accurate recordings of both of
these times would be very slim, but does anyone know
IF they have ever been recorded for a fall(s)?
Also, is it a relatively simple matter of getting a
VERY rough ESTIMATE of the spread of time by simply
dividing the length of the strewnfield by a max free
fall speed of ~ 200mph??? I know that the angle of
entry, the wind speed, the density of the meteorite,
etc., would all affect the results, and the answer
from such a simple equation would truly give ONLY an
estimate if I'm right. But WOULD this give an
approximate duration time?? For instance, if a
strewnfield is ~ 7 miles long, would it be fairly
accurate to say that meteorites were impacting over
about a 2 minute spread of time during the fall? And
if the strewnfield was ~20 miles long, impacts may
have occurred over ~ 6 minutes?
(7 miles/200mph = 0.035 hours,or = ~2.1 minutes)
(20 miles/200mph =0.1 hours, or = ~ 6 minutes)
Finally, IF all the above is even halfway accurate,
could one safely say that during a "typical" fall,
meteorites are impacting down the length of the
strewnfield for approximately 1 to 5 minutes? Or am I
way off base? If this is right, I never thought about
the concept of meteorites hitting the ground for 5
solid minutes (or more!) during a fall. That puts
thing in a different perspective, to me at least.
Thanks,
Robert Woolard
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