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why do objects burn when penetrating the atmosphere?? is it pure normal friction..or is there more to it than that??
inzomnia
05-18-09, 10:20 AM
why do objects burn when penetrating the atmosphere?? is it pure normal friction..or is there more to it than that??
Do objects burnt when penetrating atmosphere? :confused: If so, I am guessing it's because above around 110 km (from sea level), the temperature of atmosphere is above 100 oC as can be seen in following graphs (not sure which graph is more accurate, but the tendency is similar, i.e. above 90 km, the higher the altitude, the higher the temperature is):
http://pcl.physics.uwo.ca/science/lidarintro/media/Tprofilecham.gif
http://www.windows.ucar.edu/earth/images/profile.jpg
MacGyver1968
05-18-09, 10:23 AM
Most things entering the atmosphere from space are traveling at extreme speeds..well into the 10's of thousands of miles and hour. Friction from air resistance at that speed produces lots of heat. It's why the Space Shuttle has heat shield made of tiles on it's bottom.
inzomnia
05-18-09, 10:28 AM
Most things entering the atmosphere from space are traveling at extreme speeds..well into the 10's of thousands of miles and hour. Friction from air resistance at that speed produces lots of heat. It's why the Space Shuttle has heat shield made of tiles on it's bottom.
What's the speed of bullet in miles per hour?
Edit: aopps, up to just some 5000 mph :o
What's the speed of bullet in miles per hour?
An object in low oribit goes about 10x faster than a rifle bullet.
spidergoat
05-18-09, 02:42 PM
Objects that are lighter might not heat up so much, since they will slow down more quickly, and the friction with the air would be less. Besides the heat, things burn up because there is oxygen in the atmosphere.
http://inventorspot.com/articles/origami_rules_paper_airplane_set_9997
Do objects burnt when penetrating atmosphere? :confused: If so, I am guessing it's because above around 110 km (from sea level), the temperature of atmosphere is above 100 oC as can be seen in following graphs (not sure which graph is more accurate, but the tendency is similar, i.e. above 90 km, the higher the altitude, the higher the temperature is)
Those graphs show temperature, not heat ;): you would be colder as you got higher.
http://id.mind.net/~zona/mstm/physics/mechanics/energy/heatAndTemperature/heatAndTemperature.html
What's the speed of bullet in miles per hour?
Edit: aopps, up to just some 5000 mph :o
That's pretty fast for a bullet, most rifles are in the 900-1000 m/sec range (2000 - 2200 mph).
The fastest I can think of off the top of my head would be tank gun rounds ~1800 m/sec (~4000 mph), discounting experimental types.
Yes, it's friction that causes the burn-up.
inzomnia
05-18-09, 06:06 PM
Those graphs show temperature, not heat ;): you would be colder as you got higher.
http://id.mind.net/~zona/mstm/physics/mechanics/energy/heatAndTemperature/heatAndTemperature.html
Naaaaah.... :o Thanks for the link, Oli, I'm not sure that I understand it completely, yet. In accordance with your post (that it'd be colder as it got higher), the second graph shows that below 10 km, it is indeed colder when it gets higher. I'll copy the graph again so you don't have to scroll up though I don't think you need the graph at all :-P:
http://www.windows.ucar.edu/earth/images/profile.jpg
However, above 10 km, it firstly gets constant, and then between 20 and 50 km, it increases with height.. and so does above 90 km, the temperature gets higher, right? Maybe I'm still confuse with the difference between heat and temperature.. If you say it gets colder anyway, is it because the density get lower when the altitude gets higher so that the high temperature of "whatever rare things up there" couldn't create enough heat?
That's pretty fast for a bullet, most rifles are in the 900-1000 m/sec range (2000 - 2200 mph).
The fastest I can think of off the top of my head would be tank gun rounds ~1800 m/sec (~4000 mph), discounting experimental types.
Yes, it's friction that causes the burn-up.
My bad, I was wrongly converted the speed from km/h to mph, sorry for the wrong info!
However, above 10 km, it firstly gets constant, and then between 20 and 50 km, it increases with height.. and so does above 90 km, the temperature gets higher, right? Maybe I'm still confuse with the difference between heat and temperature.. If you say it gets colder anyway, is it because the density get lower when the altitude gets higher so that the high temperature of "whatever rare things up there" couldn't create enough heat?
Temperature is the energy of each molecule (to put it simply) whereas heat is more of a measure of the total - at high altitudes the molecules (although individually at high temperatures) are so far apart that there's no heat to be had: so you'd freeze :)
My bad, I was wrongly converted the speed from km/h to mph, sorry for the wrong info!
:D
inzomnia
05-18-09, 06:30 PM
Wait, Oli, I forgot to add:
However, above 10 km, it firstly gets constant, and then between 20 and 50 km, it increases with height.. and so does above 90 km, the temperature gets higher, right? Maybe I'm still confuse with the difference between heat and temperature.. If you say it gets colder anyway, is it because the density get lower when the altitude gets higher so that the high temperature of "whatever rare things up there" couldn't create enough heat?
but then when the air density get lower, isn't the friction get smaller too? And when it gets nearly vacuum (before entering atmosphere), there shall be no friction?
p.s.: you don't have to answer this for me, I'll try to google it first (tomorrow) >.>
Wait, Oli, i forgot to add:
but then when the air density get lower, isn't the friction get smaller too? And when it gets nearly vacuum, there shall be no friction?
When sufficiently high (low density of atmosphere) then yes, there'd be no friction, but re-entering space vehicles and meteors achieve speeds fast enough to encounter enough molecules that the transferred heat (energy) from impact isn't dissipated before the next one is hit: if you could re-enter slowly there wouldn't be a heat build-up.
It's a function of air density AND speed (much the same way that aircraft reach Max Q - maximum aerodynamic pressure - at altitude because being high in a thin atmosphere lets them move faster, and the speed more than offsets the drop in density).
!!!!!!!!!!!!!!!
too much info..too much new variables to consider..thanks a lot for the graph inzomnia..helped a lot..you too oli..you seem you know what you're talking about..but not intimidating:)
ok..if the object is ESCAPING the atmosphere(going up) slowly, and it is solid..then the heat would be the same as temperature,-> density won't affect it because it's solid..(molecule distance is the same, right?)..
so it'll burn because of the high heat will cause high temprature which will burn it(?)
and how are planes able to fly faster in higher altitudes?? there's less air to fly in\on right?
Objects that are lighter might not heat up so much, since they will slow down more quickly, and the friction with the air would be less. Besides the heat, things burn up because there is oxygen in the atmosphere.
http://inventorspot.com/articles/origami_rules_paper_airplane_set_9997
the O2 rates are higher up??
(crazy article btw)
ok..if the object is ESCAPING the atmosphere(going up) slowly, and it is solid..then the heat would be the same as temperature,-> density won't affect it because it's solid..(molecule distance is the same, right?)..
No the heat isn't the same as temperature, since the encounter rate will be lower (although you could make heat=temperature if you calculated the speed correctly, to match density).
so it'll burn because of the high heat will cause high temprature which will burn it(?)
Something going up slowly? (Or even coming down slowly).
No because at low speeds (lower encounter rate) the heat is low.
and how are planes able to fly faster in higher altitudes?? there's less air to fly in\on right?
Therefore less air resistance - letting them move faster.
The coefficient of lift (what keeps an aircraft up) is dependant upon speed - the faster you go the less air (or wing area) you need, therefore going fast doesn't need much air and since there isn't much the friction (and also drag due to airflow) is less.
PieAreSquared
05-19-09, 03:36 AM
so Icarus went real fast then ;)
so Icarus went real fast then ;)
Especially on the way down :D
i'm really sorry..i'm REAL lost..i'll look more into this..
i'm really sorry..i'm REAL lost..i'll look more into this..
Lost?
It's a good job I didn't even mention stagnation temperatures then. :D
lol.. no please tell me about it..i wanna sort it all once and for all..
lol.. no please tell me about it..i wanna sort it all once and for all..
If something is moving sufficiently fast it builds a "cushion" of air in front of itself, this "cushion" stays more or less fixed to the leading surfaces and gets compressed, also heating up due to that compression - and that heat can only escape one way - into the structure to which the stagnation layer is attached.
Thus causing more heat build-up.
I'm not sure (without doing extensive checks) how the temperature rises with speed, but at Mach 4 it's ~400 degrees C, at Mach 5 it's ~550 degrees C, and re-entering vehicles/ meteors are around Mach 25+, so it's a fair bet that the temperature will be very high.
In fact at one stage of re-entry the total heat is sufficient to generate plasma.
MacGyver1968
05-19-09, 10:52 AM
If something is moving sufficiently fast it builds a "cushion" of air in front of itself, this "cushion" stays more or less fixed to the leading surfaces and gets compressed, also heating up due to that compression - and that heat can only escape one way - into the structure to which the stagnation layer is attached.
Thus causing more heat build-up.
I'm not sure (without doing extensive checks) how the temperature rises with speed, but at Mach 4 it's ~400 degrees C, at Mach 5 it's ~550 degrees C, and re-entering vehicles/ meteors are around Mach 25+, so it's a fair bet that the temperature will be very high.
In fact at one stage of re-entry the total heat is sufficient to generate plasma.
Cool!! Ya learn somethin' new everyday!
Cool!!
No, HOT!
You nincompoop :p
inzomnia
05-19-09, 12:10 PM
Cool!! Ya learn somethin' new everyday!
+1. Thanks, Oli :thankyou:
!!!!!!!!!!!!!!!
too much info..too much new variables to consider..thanks a lot for the graph inzomnia..helped a lot..you too oli..you seem you know what you're talking about..but not intimidating
Do you do like this: :runaway: while posting that one? :D Oli is a design engineer and experienced in military equipments.
Do you do like this: :runaway: while posting that one? more or less,yeah..too bad there isn't a smilie for pulling one's hair..
Oli is a design engineer and experienced in military equipments
:xctd: AWESOM!!
that's what i'm gonna be in the future..:cheers:
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