# Tag Info

37

Think of temperature as average kinetic energy of the water molecules. While the average molecule doesn't have enough energy to break the inter-molecular bonds, a non-average molecule does. Water is a liquid because the dipole attraction between polar water molecules makes them stick together. At standard atmospheric pressure (acting somewhat like a vice), ...

19

It's not poop. It's fly barf. A fly spends about 25% of its time re-digesting and it only can eat liquids. It mixes the eaten food with the appropriate enzyme for digestion. The fly does this by retrieving the eaten food from its digestive system (a vomit of sorts), and drop by drop it is placed on the surface on which the fly is sitting. Only then is it ...

17

Evaporation is a different process to boiling. The first is a surface effect that happens at any time, while the latter is a bulk transformation that only happens when the conditions are correct. Technically the water is not turning into a gas, but random movement of the surface molecules allows some of them enough energy to escape from the surface into the ...

17

That is the Leidenfrost effect. If the surface is hot enough, a layer of vapor exists between the hot surface and the droplet, insulating the droplet from the full heat. The droplet levitates above the hot surface.

14

At high enough pressure you can keep water as a liquid above 100°C. With even more pressure you can even keep ice above 100°C. Similarly you can boil water at room temperature with a low pressure. (https://en.wikipedia.org/wiki/Phase_diagram) The phase diagram of water shows what state it is in at any given temperature and pressure. edit: To answer ...

11

Sprinkling water on the sidewalks will cool them down in exactly the same way that sweating cools you. In both cases it is due to evaporative cooling. The same idea has been used for millenia to cool water in hot climates. The only downside is that it will increase the humidity of the air, and humid air feels hotter than dry air because humidity slows ...

10

It actually gets a bit complicated, since several effects are involved: Evaporating water does require heat, which comes primarily from the hot stones. So throwing water on the stones does cool them down. (This is where the claim one occasionally hears, that "throwing water on the stones makes the sauna colder", comes from. Technically it's true, if one ...

8

I actually went ahead and spent some hours experimenting. Used two 500ml aluminum beer cans filled with water at room temperature, 21.4°C. One can wrapped in a paper towel soaked with an additional 20ml of water, one left bare as control. Shoved both in my small, non-ventilated house freezer at -14°C and measured temperature and weight every twenty minutes ...

7

For every temperature, there is some amount of water vapor that can exist as gas mixed in with the air. This is called the saturation pressure of water at that temperature. The relative humidity is the amount of water vapor, expressed as a percentage of the saturation pressure. As you increase the temperature, the saturation pressure increases. Steam is ...

6

Temperature is a measure for how much kinetic energy the molecules in a substance have. If the temperature is high, they are moving pretty fast, if the temperature is low, they are moving a lot slower. If molecules are moving slow, they bundle up and you get a solid. Once you heat it up a bit, the substance starts to become liquid. When you heat it up even ...

6

Temperature is a measure of the average kinetic energy of particles, characterized by a Maxwell-Boltzmann distribution. Basically, that's a fancy way to say, if something is at 25°C, a large percentage of its particles have a temperature close to 25°C, but some have a temperature farther away. When some of those particles that happen to have a temperature of ...

5

Evaporative cooling works by removing the high-velocity tail of the kinetic energy distribution. That is, only the fastest molecules escape the liquid, leaving the rest to thermalize at a lower temperature. If there is capillary action taking water to the outside of the pot and that is evaporating, then the pot cools down as it is losing heat to the leaving ...

5

While the capillary pressure in soil is many orders of magnitude lower than the atmospheric pressure, you also need to remember that in soil, the water is still in contact with the atmosphere, and thus is at atmospheric pressure plus capillary pressure. Since atmospheric pressure is orders of magnitude larger than capillary pressure, the pressure on the ...

5

yes, this is called Sublimation. Ice has a vapor pressure: Molecules will go from the solid phase to the gas phase or visa versa depending upon whether the partial pressure of water vapor in the gas phase is above or below the vapor pressure of the ice, until equillibrium is reached.

4

I will make it an answer instead of a comment. My guess is that the convergence is an optical illusion. This plane is flying at a level where the relative humidity is small.This means that the trail evaporates, it will evaporate faster from outside (the trail itself is humid) and finally what is left is merged the dissolution giving the impression of ...

4

The way your question is phrased, it looks like you are expecting the mass to change. In that case the only change will be a slight mass loss due to evaporation, but the rate of evaporation is a variable - dependant on room temperature, air pressure humidity and how still the air is above the sample.

4

It may actually work, as evaporating liquids need heat to evaporate, and water will somewhat evaporate even in the fridge. I am not sure it works in practice, because the paper also causes an adverse effect, it provides insulation, Hard to tell which effect is dominant. I'm pretty sure that the balance of both effects depends in a very large part on the ...

4

The equilibrium vapor pressure of water vapor over ice is well known and easy to google for (http://www.its.caltech.edu/~atomic/snowcrystals/ice/ice.htm is one possible link). It is slightly lower than the equilibrium vapor pressure of water vapor over liquid. Ice does not evaporate - it sublimates under those conditions. The equilibrium vapor pressures ...

3

I think it would evaporate quicker for anything we normally call a "towel". The evaporation of the plain puddle is limited by the surface area of the water. A towel provides many capillary pathways for the water to diffuse thru the fabric, eventually presenting a much larger surface are for evaporation. Other fabrics could be hydrophobic and decrease ...

3

what is the surface area of a liquid? The surface of a liquid is the interface between the liquid and (usually) the air surrounding it. The surface area is the amount of that liquid that is exposed to the air, or touching the air. And also that why the rate of evaporation increases with increase in surface area of the liquid? If more liquid is ...

3

If you are just standing on the ground and looking up, you will be able to see the base of the cloud. I suggest that your estimate for a cloud more or less directly overhead (and closer) will be more accurate than for distant clouds visible on the horizon. The altitude to the base of the clouds is called the ceiling, and can be measured using a instrument ...

3

Regarding your first question, yes, the evaporation rate is related to both the temperature of the liquid and that of the air. There is no single, universal equation describing the evaporation rate at an interface, because so many factors come into play. The simplest equation describing evaporation rate is probably that established by Langmuir: You can ...

3

If you have water in an enclosed container with some air, then the evaporation will gradually slow down towards zero. That is because the rate that liquid water molecules gain energy and become water vapor will be balanced by the rate at which water vapor molecules lose energy and become bound to the liquid. The point at which that occurs is called the ...

3

All aircraft producing lift have a wake, because the wing deflects the air downward, while the air further away is not deflected. This takes the form of a pair of "wingtip vortices". Since they transfer energy to the surrounding air as they dissipate, they expand in radius, because momentum is conserved. So they capture the condensation trails from the ...

3

I'd be very surprised if this was crystal formation. It looks to me as if the goo at the bottom of the glass formed a film, then as the film dried it shrank and fractured. The pattern of lines you're seeing are stress fractures in the film not crystals. The fracture pattern looks very symmetrical, but then you have a circular boundary condition due to the ...

3

Your instincts are right -- this is indeed crystallisation. Your original cocktail was a solution of lots of non-volatile components (sugar, Splenda, citric acid from the lemon juice, and many many other things...) in some rather more volatile solvents (ethanol and water). Only a limited amount of any of the non-volatile compounds can dissolve in a given ...

3

Is tossing out ice that forms in the buckets overnight helping with that efficiency, or are we actually throwing out valuable sucrose that could be made into syrup. There's an easy way to test: take a sample of the discarded ice, melt it, measure the volume $V$, evaporate it until only solids remain, weigh the solids, and compute the percent dissolved ...

3

Imagine spinning a roulette wheel, but instead of dropping in one ball, you drop in 100. They all rattle around at different speeds, like the molecules in water. You can cool them down by spinning the wheel slower, so they bounce about less; heat them up by spinning faster so they bounce more; you can freeze them by stopping the wheel and waiting till ...

3

It's done outside many smaller stores near where I live (Tokyo) and has zero apparent effect on the temperature. Midday summer weather is high-30s temperature and rainforest-level humidity, so the half-bucket of water tossed out the front door does little except moisten the pavement. A side effect is it tends to make the place messier - dust plus lots of ...

3

No, the temperature of the water is not that important for the performance of an evaporative cooler. This is basically because the energy needed to increase the temperature of liquid water (its specific heat capacity) is very small compared to the energy needed to evaporate the same amount of water (its enthalpy of evaporation). At room temperature the ...

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