Snow and physics
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Wjousts wrote:
The water molecules aren't reacting
I believe that they are, as they are mildly dipolar and have a resonant frequency that matches the microwave emissions of the oven. Heat is produced primarily by frictional energy losses through molecular collisions. It's quite possible to melt falling snow with microwave radiation, but terribly inefficient. Much simpler and cheaper to put salt on the road...
"A Journey of a Thousand Rest Stops Begins with a Single Movement"
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Microwaves only act on polar molecules that are free to spin back and forth. Water molecules in ice are rigidly bound and can't spin. The reason you can thaw your food out is that a few molecules of water on the surface melt due to the higher ambient temperature outside the freezer and other polar molecules in the water. Snow in a snowstorm won't melt effectively this way as a result.
3x12=36 2x12=24 1x12=12 0x12=18
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Eddy Vluggen wrote:
That would imply that I could evaporate water by cooling it?
Not at all. Evaporation removes energy from a liquid, hence it cools the liquid. Hence you have to supply energy for it to continue happening. You have to supply energy for evaporation to happen, but what you'll notice at a phase transition (e.g. water to steam) is that the temperature of the liquid doesn't change because evaporation is removing energy from the liquid.
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I got caught in a UK blizzard* on my way back from school, and that got me thinking. A microwave oven uses microwave radiation, bounced around in a box, to defrost food by the evaporation of water molecules. Would it be hypothetically possible, with a somewhat larger energy expenditure, to turn the concept 'inside out'? What I mean by this is having a device which is effectively a very powerful microwave emitter. It would melt the snow (although I wouldn't want to use it - it would probably eventually cause deep tissue damage) fairly quickly if a microwave oven is anything to go by. And if I made a few guesses, I'd think that I could make it directional so that it could melt snowballs in midair given enough power. Before I go and burn most of the hair from the surface of someone else's arms, would this be physically possible? *UK blizzard: a faint sprinkling of semi-crystallised water, which causes local governments to use up all the grit. Sometimes followed by a significantly larger dump which causes the Daily Mail to whinge.
OSDev :)
Here buy something like this: http://www.wired.com/dangerroom/2010/01/sci-fi-weapons/3/
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I got caught in a UK blizzard* on my way back from school, and that got me thinking. A microwave oven uses microwave radiation, bounced around in a box, to defrost food by the evaporation of water molecules. Would it be hypothetically possible, with a somewhat larger energy expenditure, to turn the concept 'inside out'? What I mean by this is having a device which is effectively a very powerful microwave emitter. It would melt the snow (although I wouldn't want to use it - it would probably eventually cause deep tissue damage) fairly quickly if a microwave oven is anything to go by. And if I made a few guesses, I'd think that I could make it directional so that it could melt snowballs in midair given enough power. Before I go and burn most of the hair from the surface of someone else's arms, would this be physically possible? *UK blizzard: a faint sprinkling of semi-crystallised water, which causes local governments to use up all the grit. Sometimes followed by a significantly larger dump which causes the Daily Mail to whinge.
OSDev :)
The wavelength on microwaves is rather long 3cm or so, while water and especially water vapor are very very good ad absorbing the energy(why we didnt put microwave radar on our ships, our meaning the US, was because the humidity reduced the range to uselessness). You would have to heat the water to the evaporation point which if its snow or ice would require quite a bit of energy. Put an ice cube in your microwave and see how long it takes to boil it away. your best bet would be to use a short wavelength laser(shorter wavelength = more energy generally)x rays would be better but they're ionizing and thats always bad. Theres a bunch of ways to power up lasers, they make some on chips the size of the end of a pen that can cut through soda cans w/ no problem. Once you have a laser powerful enough(couple hundred watts prolly) you need a diffuser to spread it out in a line then just fire it in front of you while you walk. or mount it under the front bumper of your car to clear paths for your tires. I have no idea if that will work, but it sounds good, and fun to build.
Please remember to rate helpful or unhelpful answers, it lets us and people reading the forums know if our answers are any good.
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Ah... Now it becomes clear. That's what I get for reading these things late at night... :-O
"A Journey of a Thousand Rest Stops Begins with a Single Movement"
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I got caught in a UK blizzard* on my way back from school, and that got me thinking. A microwave oven uses microwave radiation, bounced around in a box, to defrost food by the evaporation of water molecules. Would it be hypothetically possible, with a somewhat larger energy expenditure, to turn the concept 'inside out'? What I mean by this is having a device which is effectively a very powerful microwave emitter. It would melt the snow (although I wouldn't want to use it - it would probably eventually cause deep tissue damage) fairly quickly if a microwave oven is anything to go by. And if I made a few guesses, I'd think that I could make it directional so that it could melt snowballs in midair given enough power. Before I go and burn most of the hair from the surface of someone else's arms, would this be physically possible? *UK blizzard: a faint sprinkling of semi-crystallised water, which causes local governments to use up all the grit. Sometimes followed by a significantly larger dump which causes the Daily Mail to whinge.
OSDev :)
Unless you want cataracts, don't start fooling around trying to defeat your microwave oven's safety features. It's optical output is really high, and can kill a bird at fifty paces. It's already directional, and you can't predict how it's going to reflect. Sure it's fun to think about, but leave it at that. - Owen -
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Wjousts wrote:
but evaporation is a cooling process not a heating process
That would imply that I could evaporate water by cooling it? A gas, isn't that just a heated form of a solid? With very fast vibrating molecules? Sounds logical that if a lot of fast molecules escape, that the sum of all vibrations goes down. It's true that water becomes cooler when a bit evaporates. It's not true that evaporation is 'caused' by the cooling - it's rather a side-effect of the initial heating. Something like a ball coming back down, once you throw it up in the air :) --edit-- Throwing up is something quite different.
I are Troll :suss:
Now let's see if I can describe this without posting a text wall...
Eddy Vluggen wrote:
That would imply that I could evaporate water by cooling it? A gas, isn't that just a heated form of a solid? With very fast vibrating molecules?
Not quite. And the initial description was not 100% accurate either. The first law of thermodynamics (also known as Principle of Conservation of Energy) states that you simply can't win: you can't produce energy from nothing. The alcohol molecules lying in liquid state on your hand, need some extra energy to make the transition to gas state. They take it from your hand and the air around them. Since some (thermal) energy is drawn from your hand, you feel it's getting colder there as the molecules leave the liquid state. So the cooling process is on your hand, not the alcohol evaporation. The evaporation requires energy to happen. No extra energy means no evaporation (actually this is an oversimplification of things, as some molecules will evaporate. And if the alcohol is not in a sealed box (so that some of the runaway molecules return to the liquid state), eventually it will dry off. Blowing on it, simple desaturates the air around the liquid alcohol, thus reducing the amount of molecules returning to liquid from gas state, thus making the process faster -and your hand colder). Now a gas is certainly NOT a heated form of a liquid. There are forces at play in liquid form that are too weak in gas state, and a "normal" liquid has drastically different behaviour than a gas (or a solid for that matter). If a gas was simply a heated liquid, then the trasition between the two states would not be a violent one (as in boiling, or droplets of water on a cold glass surface when you blow on it).
Eddy Vluggen wrote:
It's true that water becomes cooler when a bit evaporates.
Hm, only under particular circumstances. If you seal the water off (in terms of energy exchange with its environment) and also if you somehow remove the molecules that escape the liquid state WITHOUT interacting with the liquid, then the remaining molecules in the water will have a smaller mean kinetic energy, meaning the liquid will have a lower temperature. However, those are two big if's there... As for the original post, well, what happened to that guard should give you a hint on the viability of such a contraption :) Yiannis Φευ! Εδόμεθα υπό ρηννοσχήμων λύκων! (Alas! We're d
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Now let's see if I can describe this without posting a text wall...
Eddy Vluggen wrote:
That would imply that I could evaporate water by cooling it? A gas, isn't that just a heated form of a solid? With very fast vibrating molecules?
Not quite. And the initial description was not 100% accurate either. The first law of thermodynamics (also known as Principle of Conservation of Energy) states that you simply can't win: you can't produce energy from nothing. The alcohol molecules lying in liquid state on your hand, need some extra energy to make the transition to gas state. They take it from your hand and the air around them. Since some (thermal) energy is drawn from your hand, you feel it's getting colder there as the molecules leave the liquid state. So the cooling process is on your hand, not the alcohol evaporation. The evaporation requires energy to happen. No extra energy means no evaporation (actually this is an oversimplification of things, as some molecules will evaporate. And if the alcohol is not in a sealed box (so that some of the runaway molecules return to the liquid state), eventually it will dry off. Blowing on it, simple desaturates the air around the liquid alcohol, thus reducing the amount of molecules returning to liquid from gas state, thus making the process faster -and your hand colder). Now a gas is certainly NOT a heated form of a liquid. There are forces at play in liquid form that are too weak in gas state, and a "normal" liquid has drastically different behaviour than a gas (or a solid for that matter). If a gas was simply a heated liquid, then the trasition between the two states would not be a violent one (as in boiling, or droplets of water on a cold glass surface when you blow on it).
Eddy Vluggen wrote:
It's true that water becomes cooler when a bit evaporates.
Hm, only under particular circumstances. If you seal the water off (in terms of energy exchange with its environment) and also if you somehow remove the molecules that escape the liquid state WITHOUT interacting with the liquid, then the remaining molecules in the water will have a smaller mean kinetic energy, meaning the liquid will have a lower temperature. However, those are two big if's there... As for the original post, well, what happened to that guard should give you a hint on the viability of such a contraption :) Yiannis Φευ! Εδόμεθα υπό ρηννοσχήμων λύκων! (Alas! We're d
yiangos wrote:
If a gas was simply a heated liquid, then the trasition between the two states would not be a violent one
I'll stop calling a gas a heated liquid. Somehow they remind me of different
viewfor the sametable- just different representations. The way you're explaining it, it's not a different representation, but a conversion. Something like going from HTML to RTF. My gratitude for the explanation :thumbsup:I are Troll :suss:
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"Not all that glitters is gold, and not all who wander are lost" :) The word "Troll" has multiple meanings, and it's also the name of a race in World of Warcraft. It's a suggestive sig without that particular part of information. ..and there you got the hardest part of our profession. It's easy to create a table to save some information on employees. Now the user has a different idea on what an employee is then I do, and that's the hard part.
I are Troll :suss:
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yiangos wrote:
If a gas was simply a heated liquid, then the trasition between the two states would not be a violent one
I'll stop calling a gas a heated liquid. Somehow they remind me of different
viewfor the sametable- just different representations. The way you're explaining it, it's not a different representation, but a conversion. Something like going from HTML to RTF. My gratitude for the explanation :thumbsup:I are Troll :suss:
Eddy Vluggen wrote:
The way you're explaining it, it's not a different representation, but a conversion. Something like going from HTML to RTF.
It's a conversion, it's deterministic macroscopically, and it has a rather simple (but not too simple) conversion function. Sort of like a
switchwith 3 cases per transition. Check this: http://en.wikipedia.org/wiki/Cooling_curve[^] This graph shows what happens to the temperature of a material(the temperature is related to the mean kinetic energy of the molecules, irrespective of state) as it goes from liquid (far left, smooth decline) to solid (far right, smooth decline again). Notice the sharp angle and the plateau that occurs at "freezing" temperature. Sharp angles in physics denote violent changes. Here, when the liquid (say, water) reaches this temperature (for water, 273 Kelvin), the temperature in the water stops dropping although we continue to pump heat out of it (by using e.g. a freezer). In this transient state, both ice and water co-exist, as some molecules have so little internal energy left, that the binding forces that keep them together forcefully bind them to a lattice, stopping any "attempt" to escape or move freely. Other molecules still have enough energh to overcome this attraction, and still move as if they're liquid. The heat taken from water to convert it from water of 273 Kelvin (or 0C, or 32F) to ice of the same temperature is called latent heat, and it's a distinct characteristic of the material itself. A similar curve exists for the transition between liquid and gas. The funny thing is that under pressure, the width of the plateau in that graph changes, and also the temperature at which it occurs changes. For instance, gas inside a can of spray is at such high pressure, that even in room temperature, it's a liquid. Above a certain value of pressure (dependent on the material as well) it actually vanishes. At such high pressure, it makes no sense to talk about gas, liquid or solid state. There's no real distinction between the three. We believe that this is what goes on deep inside the gas giant planets of the solar system. By the way, it's fun th check out the qualities of superfluids[ -
Eddy Vluggen wrote:
The way you're explaining it, it's not a different representation, but a conversion. Something like going from HTML to RTF.
It's a conversion, it's deterministic macroscopically, and it has a rather simple (but not too simple) conversion function. Sort of like a
switchwith 3 cases per transition. Check this: http://en.wikipedia.org/wiki/Cooling_curve[^] This graph shows what happens to the temperature of a material(the temperature is related to the mean kinetic energy of the molecules, irrespective of state) as it goes from liquid (far left, smooth decline) to solid (far right, smooth decline again). Notice the sharp angle and the plateau that occurs at "freezing" temperature. Sharp angles in physics denote violent changes. Here, when the liquid (say, water) reaches this temperature (for water, 273 Kelvin), the temperature in the water stops dropping although we continue to pump heat out of it (by using e.g. a freezer). In this transient state, both ice and water co-exist, as some molecules have so little internal energy left, that the binding forces that keep them together forcefully bind them to a lattice, stopping any "attempt" to escape or move freely. Other molecules still have enough energh to overcome this attraction, and still move as if they're liquid. The heat taken from water to convert it from water of 273 Kelvin (or 0C, or 32F) to ice of the same temperature is called latent heat, and it's a distinct characteristic of the material itself. A similar curve exists for the transition between liquid and gas. The funny thing is that under pressure, the width of the plateau in that graph changes, and also the temperature at which it occurs changes. For instance, gas inside a can of spray is at such high pressure, that even in room temperature, it's a liquid. Above a certain value of pressure (dependent on the material as well) it actually vanishes. At such high pressure, it makes no sense to talk about gas, liquid or solid state. There's no real distinction between the three. We believe that this is what goes on deep inside the gas giant planets of the solar system. By the way, it's fun th check out the qualities of superfluids[yiangos wrote:
Sort of like a switch with 3 cases per transition
That "sort of" made me somewhat uneasy, but you were referring to the number of states that a substance can have. And there are more states than the three that I learned at school. ..but liquids that climb up a wall and "escape" from a cup? Sounded more like voodoo than physics! Thanks for the explanation :)
I are Troll :suss:
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I got caught in a UK blizzard* on my way back from school, and that got me thinking. A microwave oven uses microwave radiation, bounced around in a box, to defrost food by the evaporation of water molecules. Would it be hypothetically possible, with a somewhat larger energy expenditure, to turn the concept 'inside out'? What I mean by this is having a device which is effectively a very powerful microwave emitter. It would melt the snow (although I wouldn't want to use it - it would probably eventually cause deep tissue damage) fairly quickly if a microwave oven is anything to go by. And if I made a few guesses, I'd think that I could make it directional so that it could melt snowballs in midair given enough power. Before I go and burn most of the hair from the surface of someone else's arms, would this be physically possible? *UK blizzard: a faint sprinkling of semi-crystallised water, which causes local governments to use up all the grit. Sometimes followed by a significantly larger dump which causes the Daily Mail to whinge.
OSDev :)
It's possible to use microwaves to melt snow, but you wouldn't be able to just turn the microwave oven inside out, that could take hours, if it did anything at all. :( As for the snowball, you would need A LOT of power to melt it that fast, and it would have to be focused all on the same point... Fun idea though :) Oh, another thing too, if you were planning on building something like this, just know that microwave ovens have gigantic capacitors in them (to create the radiation), which is not good if you happen to be taking one apart. :( That raccoon started it.