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Re: (meteorobs) Fwd: Meteorite said to start backyard fire
Jeff Rupert asks:
>Okay, I'm not an expert, and I don't need a big long explanation, but
>I am curious as to where the friction stops and maybe a little info
>about that. After that does it fall at 32 feet per second squared or
>is it something else?
Great question, Jeff! I'm no expert on meteor trajectories or the physics of
meteor flight. But the short answer as I understand it, is most meteoroids
lose all of their celestial velocity relative to earth at an altitude above
ground of well over 30km (20 miles). At that point, they have simply become
"falling rocks" - in free fall. As such, they will continue to be pulled down
by gravity, while at the same time being buffeted by wind resistance. And so
they eventually reach their "terminal velocity", generally striking earth's
surface at between 200 and 500 miles an hour - or so I recall, anyway!
In fact, the vast majority of meteoroids are ablated so rapidly that they just
"dissipate" or "burn up", upon entry into the atmosphere. (Remember the LOWEST
atmospheric impact speed for a meteoroid is about 24,000 miles per hour. And
many or most meteoroids are roughly the density of water, or even less!) But
of the few that survive, essentially all go through this period of free fall,
or "dark flight". Only the most massive and dense objects actually ever reach
earth's surface with enough kinetic energy to ionize the air around them!
That said, I stand corrected by Ed Majden's excellent comments - there ARE it
seems meteorites that reach the ground warm! And Ed, if I understand your post
correctly, that residual warmth does NOT come from a meteoroid's fiery entry
into the air, but rather from solar heating of the object in the atmosphere?
Clear skies,
Lew Gramer
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