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Tom Mazanec
2018-Sep-19, 01:17 AM
Is it friction or air compression? I've read both versions.

Jens
2018-Sep-19, 01:34 AM
Iím just guessing, but I would suppose that it is some of both, but that the compression is dominant considering the shape and speed. It will compress a lot of air, and some of the air will create friction as it flows along the surface.


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DaveC426913
2018-Sep-19, 01:40 AM
If my reading is correct, it is actually the shock front ahead of the meteor.

DaveC426913
2018-Sep-19, 01:43 AM
Good article:
https://physics.stackexchange.com/questions/288689/why-do-meteors-heat-up-when-they-fall-through-the-atmosphere

Tom Mazanec
2018-Sep-19, 01:50 AM
Good article:
https://physics.stackexchange.com/questions/288689/why-do-meteors-heat-up-when-they-fall-through-the-atmosphere

Yeah, good article. Two people answered the question. First said compression, second said friction.
See what I mean?

CJSF
2018-Sep-19, 11:56 AM
Yeah, good article. Two people answered the question. First said compression, second said friction.
See what I mean?

You may have noticed the first answer has more "up votes" and is more comprehensive and supported than the second. I am not saying that automatically equates it with being correct, but it should be of some consequence. If I recall what i've learned about it, the primary reason is the compression, with friction effects being secondary. Which is unfortunate, because it takes another otherwise science-pithy They Might Be Giants song out of the running for my signature.

https://www.youtube.com/watch?v=JqBChyNyLhU

CJSF

George
2018-Sep-19, 03:12 PM
It's my understanding that a meteoroid will still be very cold when it lands. The ablation process removes most of the heat.

Tom Mazanec
2018-Sep-19, 04:12 PM
It's my understanding that a meteoroid will still be very cold when it lands. The ablation process removes most of the heat.

My understanding is that is if it is stoney or partially stoney. If it is metallic the metal conducts the heat enough for it to be hot. Is that true?

Roger E. Moore
2018-Sep-19, 04:18 PM
My understanding is that is if it is stoney or partially stoney. If it is metallic the metal conducts the heat enough for it to be hot. Is that true?

When Sputnik IV crashed in Wisconsin in 1962, metallic pieces of it were too hot to handle at first.

https://www.wpr.org/vintage-wisconsin-when-piece-sputnik-iv-fell-wisconsin

DaveC426913
2018-Sep-19, 04:34 PM
Which is unfortunate, because it takes another otherwise science-pithy They Might Be Giants song out of the running for my signature.
Huh. They're usually pretty accurate.

I wonder .. do you suppose they actually have a scientist consultant on retainer to review their lyrics?

CJSF
2018-Sep-19, 04:58 PM
Huh. They're usually pretty accurate.

I wonder .. do you suppose they actually have a scientist consultant on retainer to review their lyrics?They do not, according to John Flansburg...

CJSF

Tom Mazanec
2018-Sep-19, 09:07 PM
For what it's worth, most of the explanations I see tend to be friction.

Noclevername
2018-Sep-19, 09:40 PM
When Sputnik IV crashed in Wisconsin in 1962, metallic pieces of it were too hot to handle at first.

https://www.wpr.org/vintage-wisconsin-when-piece-sputnik-iv-fell-wisconsin

But Sputnik was a hollow shell, meteors are mostly solid. Wouldn't that internal mass act as a heat sink?

profloater
2018-Sep-19, 10:02 PM
When you go supersonic there is a compression wave which causes the air to heat. To heat the object you will have conduction across the boundary layer and radiation. The boundary layer will be turbulent at very high reynolds number and that means more able to transfer heat to the object from the air. Friction is a cover all for viscosity effects. As speed increases the compression heating and radiation will become more significant. Then the surface gets so hot it decomposes and that can happen faster then inward conduction but that will depend on the materialsí conductivity and high temperature properties. Ordinary supersonic flight incurs significant heating of the airframe from the area behind the shockwave, it limits the supersonic range. Concorde for example heated its fuel to absorb skin heat but a meteor is going much faster.

Jens
2018-Sep-19, 10:26 PM
When Sputnik IV crashed in Wisconsin in 1962, metallic pieces of it were too hot to handle at first.


That may be true, but a meteorite that has just landed will be cold, not hot, because it is only the surface that gets heated, and the bulk remains cold. If you are interested, the is an XKCD What If episode that deals with whether you can cook a piece of steak by dropping it from space.


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PetTastic
2018-Sep-20, 09:13 AM
Does the answer to this vary with speed?

Sputnik was only travelling at orbital velocities, Concord only supersonic but meteors are much faster.

I think, ram-air effects on meteors generate a layer of plasma hot enough to generate soft x-rays?

profloater
2018-Sep-20, 09:31 AM
Does the answer to this vary with speed?

Sputnik was only travelling at orbital velocities, Concord only supersonic but meteors are much faster.

I think, ram-air effects on meteors generate a layer of plasma hot enough to generate soft x-rays?
I dont know about xrays but the faster the more heating in the air. Once you are supersonic the shock wave is a kind of instant compression which directly heats the air and of course applies a retarding force, it’s the momentum that is converted into energy. The shape of the shock wave sweeps back therefore getting closer to the meteor, and thus heating more effectively.

Grey
2018-Sep-20, 03:04 PM
That may be true, but a meteorite that has just landed will be cold, not hot, because it is only the surface that gets heated, and the bulk remains cold. If you are interested, the is an XKCD What If episode that deals with whether you can cook a piece of steak by dropping it from space.Here (https://what-if.xkcd.com/28/)'s the link, for anyone interested.

PetTastic
2018-Sep-20, 08:26 PM
That may be true, but a meteorite that has just landed will be cold, not hot, because it is only the surface that gets heated, and the bulk remains cold. If you are interested, the is an XKCD What If episode that deals with whether you can cook a piece of steak by dropping it from space.

Tapatalk

After you drop a steak from that height does the 3 second rule still apply?

Most meteors arrive at the top of the atmosphere considerably faster than if they were just dropped.

Heating methods that have been suggested for objects travelling fast enough include hard x-rays penetrating deep into the objects at kilowatts per square metre, and induction heating from plasma disturbances.
I have not investigated how realistic these are but if they were to happen thermal shock would probably cause the meteor to breakup and airburst.

Jens
2018-Sep-20, 11:49 PM
After you drop a steak from that height does the 3 second rule still apply?



I think it depends where it falls. If it's pure white snow, then definitely. If the snow is yellow, not so much.