# Tag Info

163

Both thawing and evaporation involve heat exchange between the stone tile, the water sitting atop the stone tile, any water that's been absorbed by the stone tile, and the air around. The basic reason that the center and the edges of the tile evaporate differently is that the gaps between the tiles change the way that heat is exchanged there. However the ...

103

Water vapour is a clear and colourless gas, so it can't be seen by the naked eye. What you see in the photo in your second link is (partially) condensed water vapour, i.e. fog (or mist). Fog contains tiny, discrete water droplets and light bounces off their surface in random directions, causing the visibility. Water vapour by contrast only contain free ...

65

If the air was still, body heat warms a thin layer of air next to the skin. This warm air would stay near the skin, separating it from the cold air. Wind, however, continuously blows away this warm bit of air, replacing it with the colder surrounding air. There's a similar effect on humidity. Evaporating sweat increases the humidity right next to the skin, ...

53

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), ...

52

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 ...

51

Water molecules are polar; this basically means that they have a "positive side" and a "negative side" Salt is composed by Na$^+$ and Cl$^-$ ions held together by electrostatic forces (is a ionic compound). When salt is put into water, it dissociates, i.e. the Na$^+$ ions are separated from the Cl$^-$ ions. When in the water, such ions are surrounded by ...

49

[Already said] A blackboard is not porous, i.e. it actually never takes up much water from the sponge in the first place (and if you were to squeeze out more than a little, it would just run down to the bottom). [Already said] Yet the surface is hydrophilic, i.e. the water that does stay on the board forms a very thin film instead of droplets (as you'd get ...

45

Sure it can melt. Ice is less dense than liquid water. The difference in volume (the molten water will not fill the cube completely) is filled with water vapor. In case you are wondering why water vapor is created: You might have seen the experiment where water starts to boil if you put it in vacuum. If there is no vacuum pump to remove the vapor, the ...

43

The soda can't escape through a sealed can, which leaves two options: the can wasn't sealed or the soda didn't escape. Soda didn't escape: This is the less likely and less interesting case: the can was produced defective and never had any soda in it. Issue on the manufacturing line, and whoever saved it (you/parents?) did so because that was novel, and ...

43

Yes, as other answers have stated, the temperature could drop below room temperature through evaporative cooling. In fact it could get as cold as the wet-bulb temperature of the air in the room. If you know the temperature and humidity of the air, you can figure out the wet-bulb temperature by using a psychrometric chart: Find your room temperature on the ...

40

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.

34

According to @rob , "The basic reason that the center and the edges of the tile evaporate differently is that the gaps between the tiles change the way that heat is exchanged there. " This sounds reasonable. However, I'd like to offer some other tentative explanations. First of all, let me note that the tiles in the image look unglazed and, therefore, their ...

31

Firstly, to make a valid comparison between how water and air 'feels' on your skin, two conditions would need to be met: Both water and air would have to be at exactly the same temperature. That temperature would have to be lower than human body temperature (strictly speaking skin temperature). If those conditions are met then water would certainly feel ...

30

The answer is a combination of physics and physiology. The warm water in the shower very quickly heats up the air in the shower, and warms up your skin. It also drives up the humidity of the air in the shower. You acclimate very quickly to the temperature/humidity conditions in the shower as being "normal". With the door left open a crack, you allow ...

29

Hanging it along the diagonal will maximize the surface area, but while the corners will dry faster, the thickest area with two layers will not. A simple way to speed up the process is to flip the towel over after some time to expose the wet insides. Or using clothespins to avoid the slow drying double layer alltogether

25

Not everything is evaporating. You raise the point that we can "smell" certain metals which, given how you smell most things would imply that the metal is evaporating somehow and entering your nose. You'd be right to think this is strange and in contradiction with the idea that metallic bonds tend to be strong and so unlikely to evaporate. This is a good ...

24

Trouble is caused by definitions of steam and vapour in physics and in common language. Physical definition of water vapour and steam is gaseous phase of water. In common language it is "the white cloud above pot with warm water in it when it is cold there". Take glass kettle and put it on a stove and boil the water in it. You will see bubbles growing in ...

23

The sides and corners of the cube are a few degrees warmer than the center. They are there for the same reason that an ice-cube's corners go round, and the same reason that square stones lose their corners first in the river. They aren't precisely circles, they are rounded squares also known as squircles. What would a child think of that word? You can ...

22

I’ve had numerous experiences with unopened old cans of soda losing part of their contents, though my cans were no where near as old as yours. I do remember one being empty. The snap top tabs probably don’t make a perfect seal. That combined with the positive pressure of the carbonation might result in very slow escape of the carbon dioxide gas, probably ...

20

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 ...

20

Microscopically, both the water molecules in the air and the water molecules on the clothing are rapidly moving around due to their thermal energy. Every once in a while, a molecule on the clothing will have enough energy to break free; every once in a while, a molecule in the air will stick to your clothes. Because the humidity in your room is less than 100%...

19

Although flat the blackboard has a texture so that when a damp cloth is rubbed across it the water adheres to the board and isolated droplets are not formed. So you have a fairly uniform thin film of water across the board which is ideal for evaporation.

17

When a solid or liquid body is immersed in a gas (e.g. ordinary objects sitting in a room full of air) the thermodynamic equilibrium is a dynamic equilibrium in which there is a non-zero vapour pressure of the material of the object in question. That is to say, if you first replaced all the air by clean air, then afterwards the object would start to ...

16

Others have emphasised the effects of evaporation, but I'd suggest another key factor is likely to be related to several features of the grouting that make the edges dry sooner. Firstly, the fact that the grout sits at a lower level from the top of the tile means moisture will tend to migrate to the lower level - and it will "drain" from the edges of the ...

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 Phil'...

14

Yes, it can become cooler than room temperature. The fan blowing on the liquid surface acts like the evaporation stage in a refrigerator. There's no recycling of the vapour by condensation as in a refrigerator, but that's clearly not important here! It's no doubt possible even to freeze the liquid, but this is more easily demonstrated by blowing air at room ...

13

I would suggest an alternative explanation: the tiles are not, in fact, perfectly flat. "Flat" floor tiles actually have a degree of acceptable curvature when manufactured (similar to this list of deviations) which is small enough that it's not visible, and - as you will have doubtless observed in older tiles - tend to wear more at the centre over time, ...

12

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 ...

12

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 ...

12

The relative humidity of air is pressure dependent. Your method of popping your ears involves increasing the pressure of the air in your mouth. And if you sufficiently compress a volume of air that has a high relative humidity, you can increase the air's relative humidity beyond it's saturation limit, which causes the water vapor in the air to start to ...

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