| Doug McLaren wrote:
| > | I would expect ANY solid object entering the atmosphere at high
| > | velocity to show a hot entry
Certainly common sense would lead one to believe this. But it's not
that simple ...
| > Actually, when a meteor lands, it's usually not even hot.
| > The outer parts of it often ablate off, leaving the cooler candy
| > center inside, and once it gets into the thicker part of the
| > atmosphere, it slows to terminal velocity and has several minutes to
| > cool off.
| More or less bollocks.
Less rather than more, obviously.
Depends on the size and speed/angle of the meteor when it enters our
atmosphere. If the meteor is huge, our atmosphere will do almost
nothing to it and it'll smack into the ground at almost full speed.
(And if it's big enough, it'll spawn the creation of a major motion
picture or just kill everybody on the planet.) But if it's smaller,
it certainly does slow to terminal velocity, which is probably less
than 500 mph.
| > The reason that space craft re-entering get so hot is that they're
| > going around 16,000 mph when they hit the atmosphere, and they need to
| > bleed off all this speed. If a metor just happened to hit our
| > atmosphere without much velocity (it could happen under the right
| > conditions)
| It actually couldn't. Gravitational potential makes sure of that.
Apparantly there is a minimum speed that a meteor can enter our
atmosphere from space. I was thinking that if it came in just right
it could hit our atmosphere with very little kinetic energy relative
to our planet, but apparantly not. I could work out the math of this
and verify it myself if I wanted to, but for now I'll take their word
for it, that anything natural that hits our atmosphere is going very
Apparantly this minimum speed is 11 (kps) kilometers per second.
You can find a reference to this minimum speed at
Other pages you might find useful include :
`Are meteorites hot or cold when they hit Earth?'
(answer: could be either one.)
`Do meteors slow down to terminal velocity?'
(answer: yes, in most cases, unless it's a very large meteor. But
most are small.)
And here's an article about a meteor that hit a car, complete with
considering that the final meteorite weighs 27 pounds, if it hit the
car doing 11 kps (and the measured speed from the videos taken is even
higher), the car would have been utterly disintegrated, not just
smashed up. It probably hit the car at a few hundred mph.
(An object at 11 kps has almost _7000_
times the kinetic energy of one
at 300 mph.)
Also consider that this particular meteorite was so spectacular that
there were many eye-witnesses, and 16 people even were able to film
it. It has been very well studied.
| Thatas about tantamounyt to saying thata frictionbaless ball will roll
| to a stop at the bottom of a pudding bowl. No matter ehere you strat it
| from it won't.
This analogy is extremely apt outside out our atmosphere (and I'm
sutiably impressed. Seriously.), and I'll concede that a meteor must
have a minimum speed to reach our outer atmosphere. (Well, I already
However, once it hits our atmosphere, your frictionless analogy
completely falls apart.
| The only metioors tha arrive 'slowy' are teh ones that start here.
Well, it depends on how you define slowly. 200 mph isn't slow in
terrestrial circles, but it's certainly slow in celestial circles,and
meteorites certainly do land at that speed.
| > If the Weekly World News said they'd found Martian meteorites, I'd
| > probably skip over that and look for more pictures of the batboy. But
| > if NASA does, well, it's probably worth reading, and I haven't done
| > more than skim over the stuff so far.
| Just because a rock has te same composition as a bit of Mars doesn't
| mean it comes from there.
I haven't read all the stuff yet. As mentioned before, I'm skeptical,
but given the credentials of the people who have made the claims, I'm
not going to dismiss them out of hand. (If you want to, feel free.)
| > Ultimately, I consider myself to be reasonably smart.
| Try education as well.
You first. You've certainly made more factual errors in this thread
(and presented them more authoritatively, I might add) than I have.
In any event, this thread has certainly taken on a life of it's own, a
life totally unrelated to R/C. We really should let it die. (Yes, I
know, I'm contributing to it too.)
Ob R/C related:
Anybody know what this plane is?
It's got a 6' wing span (and no dihedral), and an 0.40 OS MAX FP
engine. (Sounds like it's a bit underpowered.) Got it off of a local
freecycle list. Needs some work, but it's not in that bad of shape.
I suspect it's a Telemaster, but I'm not sure.
Doug McLaren, firstname.lastname@example.org
"Only drug dealers and software companies
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