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Post by Moon Man on Nov 15, 2005 16:25:13 GMT -4
Because different people have given different answers. For example, if you throw cold water in space it freezes. If you throw hot water in space it freezes just as fast as cold water. So the object doesn't really matter everytime.
Explain that!
And I mean 250 miles up in space.
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Post by BertL on Nov 15, 2005 16:35:31 GMT -4
[...] For example, if you throw cold water in space it freezes. If you throw hot water in space it freezes just as fast as cold water. So the object doesn't really matter everytime. Explain that! And I mean 250 miles up in space. What does this have to do with the 'temperature of vacuum'? I don't know much about how fast water freezes in space, so I'll ask you this. What are you basing it on?
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Post by nomuse on Nov 15, 2005 16:46:46 GMT -4
Technically, it sublimates.
You have to define what form this water is in. If you, say, put a typical ice-cube in space it would first crack, disintigrate even, due to the pressure of internal air bubbles. If we prepared a bubble-free ice cube, then if put in space it would simply hang there...very, very slowly it would come to thermal equilibrium with the 4K background radiation.
Unless we expose it to some larger radiant source -- say, the sun. Then the outer layers of the ice boil away. We observe the same effect every time a comet comes in-system.
Think of water on the Moon's surface. It is ice if it is not exposed to sunlight. It is not there, and no longer water, if it is exposed to sunlight.
*by "no longer water" I meant that most of the water molecules will actually be broken up into hydrogen and oxygen by the sunlight. Oh, and some of these gas molecules will be ionized as well, but that's beside the point.
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Post by Glom on Nov 15, 2005 17:16:06 GMT -4
Do you believe it is not cold in space or do you believe the temperature is simply not measurable..? For vacuum, for all applications related this issue, it is neither hot nor cold. Vacuum is the absence of matter. As I said before, temperature is property of matter, just like colour. No matter => no temperature. Temperature has no meaning for a vacuum. All temperatures you will find for space refer to specific objects in specific conditions and are often a gross simplification of the thermodynamic problem (ie they're useless figures for this purpose). Lets say it's a sunny 220 degree day. What would the temperature be in a shadow..? That's a bit vague. I'm going to assume you are referring to the surface (ie the regolith). It depends on the thermal conductivity of the regolith, the temperature of the surrounding regolith (as I have said before, without convection to smoothen out temperature variations, the temperature of regolith only a few metres away could be radically different), the radiative properties of the regolith, the incidence of any electromagnetic radiation from other sources. Also, it depends on how changeable the conditions are. If they are relatively changeable, then the regolith will not have had time to reach thermal equilibrium and so the temperature will be changing. I don't have a super computer handy so I couldn't compute the temperature field of the surface regolith. If you say it's not measurable because only an object is subject to a temperature then just tell me if you believe it would still 220 degrees in the shade..? See above. Do you believe that on a bright sunny day that there would be shadows cast from an astronaut..? Of course. If you say it depends on what time of day then assume the sun is at it's highest point. Fine, but it's not that relevant given that the surface excursions were during the morning, which lasts a week. Do you believe the sun shines brighter on the moon than it does on earth..? Not significantly. There is some absorption of infrared due to the atmosphere, but it's not that big a deal.
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Post by Moon Man on Nov 15, 2005 17:26:28 GMT -4
Welcome Bert. It was just a general question and has no bearing on a temperature in a vacuum.
Thanks nomuse.
Okay, lets say it's 10 pm at night, so it's dark out. You have hot water in a thermos and you open the thermos and throw the water into space.
At the same time you have cold water in a thermos and you open the thermos and throw the water into space.
I believe they will both instantly freeze.
Yes or no..?
Please don't say it's dark so you couldn't see what happened to the water..Ha!
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Post by BertL on Nov 15, 2005 17:28:49 GMT -4
You can't base stuff like that with "I believe", Moon Man. For me, the question remains unanswered until somebody has planted any scientific backgrounds on the table.
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Post by nomuse on Nov 15, 2005 17:31:47 GMT -4
Depends on the time scale of "instantly."
I'll have to defer to someone with a stronger background in thermodynamics to answer this one. Time also depends on how vigorously you agitate the stream during the "throw"; if it comes out in a big lump the heat transfer through the mass will be slower, than if you've managed to break it up into fine droplets.
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Post by Glom on Nov 15, 2005 17:34:10 GMT -4
I believe they will both instantly freeze. You're wrong. The coffee will boil because of the low pressure. Do you know about phase diagrams?
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politik
Venus
on a crusade against ignorance
Posts: 83
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Post by politik on Nov 15, 2005 17:38:48 GMT -4
Thanks politik. The first question warrants elaboration. Never mind temperature readings. Is it cold in space..? I say yes, others have said yes, while others have said no it's not cold. What exactly needs elaboration? There is no temperature in space. Empty space doesn't have a temperature. However, the temperature of an object will differ depending on the proximity of other objects in outer space, such as a star or planet. Lets compare Mercury with the moon. Both bodies are heavily cratered, geologically dead, no atmosphere, have ancient surfaces, and littered with boulders and pulverized dust. The surface of Mercury however has an extreme surface temperature range, more so than the moon. On average, the surface of Mercury can be as low as 100K to as high as 700k! The moon however has a range of 100k to only 400k. Why is it so much hotter on Mercury? The answer is simple: it is much closer to the Sun. Despite this proximity, the surface temperature will cool to 100k on the dark side, the same as the moon! My point is if empty space had a temperature, than wouldn't it be subject to the same effects from the sun? shouldn't "space" near the sun be hotter? If so, how is it that Mercury can cool to the same temperature as the moon? Again the answer is obvious. There is no temperature in space. Therefore it cannot effect the temperature of any object or planetary surface.
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Post by nomuse on Nov 15, 2005 17:46:38 GMT -4
So...assuming no sunlight or other radiant source, the water essentially "blows apart" (due to being well over boiling temperature), then as the droplets radiate they freeze out into crystals? Seems to me, shape aside, the hot water will still have more latent heat and will take longer to freeze. Or am I misreading the actual process?
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Post by Moon Man on Nov 15, 2005 17:47:56 GMT -4
Thanks Glom. This may sound silly but I don't think it is. On a bright clear sunny summer day on earth I don't remember seeing a shadow of myself everyday. I never really looked to make sure but I don't recall seeing one. This argument just came to me since I joined BA.
Do you believe we always see a shadow on earth even on a brightest summer day..?
Also, since HBers claim the photos were faked I always wondered why a HBer never attempted to recreate the picture to measure the shadow. It would be lots of work to do but I think it could be done and I'm surprise someone hasn't tried it yet.
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politik
Venus
on a crusade against ignorance
Posts: 83
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Post by politik on Nov 15, 2005 17:52:02 GMT -4
So...assuming no sunlight or other radiant source, the water essentially "blows apart" (due to being well over boiling temperature), then as the droplets radiate they freeze out into crystals? Seems to me, shape aside, the hot water will still have more latent heat and will take longer to freeze. Or am I misreading the actual process? The question is silly. They will both evaporate almost instantly, but the hot water even faster. The time difference would be so small you'd have to slow down time to measure it. But the difference would still be there
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Post by Moon Man on Nov 15, 2005 17:52:03 GMT -4
I believe they will both instantly freeze. You're wrong. The coffee will boil because of the low pressure. Do you know about phase diagrams? No, I'm struggling to understand some of this stuff. Feel free to enlighten me please.
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politik
Venus
on a crusade against ignorance
Posts: 83
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Post by politik on Nov 15, 2005 17:58:00 GMT -4
Thanks Glom. This may sound silly but I don't think it is. On a bright clear sunny summer day on earth I don't remember seeing a shadow of myself everyday. I never really looked to make sure but I don't recall seeing one. This argument just came to me since I joined BA. Do you believe we always see a shadow on earth even on a brightest summer day..? Are you seriously contending that a shadow is not always produced by an object blocking the Sunlight?
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Post by Jason Thompson on Nov 15, 2005 17:59:51 GMT -4
Moon Man, you overlook the effects of pressure.
In on of my previous jobs we used a machine called a Speedvac. It is basically a centrifuge with a vacuum pump attached. If you put a small tube of water inside it (well, two really, since you need to balance the centrifuge rotor!) and switch it on the water can be boiled off by simply lowering the pressure inside the chamber. If you completely evacuate the chamber the water will freeze. This happenes because the top layer of water evaporates, taking energy away from the water beneath and cooling it. When I open the machine the tubes are cold to the touch, but only the parts with ice inside. The top of the tube, and the machine itself, remains at the temperature it was when I started. In fact, if anything the mechanical operation has caused the machine to warm up a bit.
Now, when there was a vacuum in the chamber, was it cold or warm? If it was cold why was the machine still warm? If it was warm how was the ice able to form? The vacuum itself was neither. The effect of the vacuum was to allow the water to change state and hence change its own temperature, but the solid machinery was unable to do this.
This is why we get so frustrated. You just won't grasp that a vacuum cannot have a temperature. Objects in a vacuum can, but not the vacuum itself. The freezing of water in space will happen whether you are in shade or sunlight, since it is primarily an effect of pressure in your experiment.
(For anyone who is interested, we used the Speedvac to freeze-dry proteins and nucleic acids for storage or transport. Leave the vacuum on long enough and the ice will sublime completely.)
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