# Tag Info

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 ...

15

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 ...

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 ...

6

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 ...

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 ...

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

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 ...

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.

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

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 ...

2

Instead of temperature drop, we have to to consider amount of heat transferred to the building from the wildfire. The temperature of the structures will rise towards the ignition point depending on the temperature and closeness of the heat source. Cooling can then slow down the heating or in best case stop it completely. The heat transfer is is a ...

2

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 ...

2

It gets cooler. It feels hotter. Saunas are generally around 80-110 degrees Celsius, and very low humidity (steam rooms are much lower temperatures, and very high humidity). The temperature we sense is dependent on humidity. Putting water on the stones means that lots of energy from them goes into turning the water into steam & vapour. That's energy ...

2

Your body can increase its heat loss by evaporating water from its surface. Blood is then directed to the surface of your body to cool it, so that it can maintain an internal temperature of 36.8 Celsius, say. If the humidity is higher, your body cannot lose as much heat by evaporation. See here, say, or the Google search that got me there. So, you are hotter ...

2

I would say it's condensation. And the air humidity is pretty high, after all that's what saunas do... Basically stones don't radiate heat into the air that well. Air is mobile, but not a good conductor. But, liquid water gobbles up heat pretty fast. It becomes steam, which is mobile and spreads around pretty quickly. The air becomes saturated with ...

2

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 ...

2

The vapor pattern that we can see on this pictures is due to the instability of trailing edge vortices. Here are some picture showing an instability of this vortices (in French for English see aslo this JFM). Different plane will have different trailing edge vortices resulting in different observable vapor pattern. On Wikipedia the trailing edge vortex are ...

2

Water vapour at the Earth's surface consists of molecules of water mixed up with molecules of oxygen and nitrogen. At room temperature 100% relative humidity is about 20g of water per kilogram of air (roughly a cubic metre), so about 4 molecules per 100 are water. To get water vapour in a vacuum you just remove the air molecules and leave the 20g per cubic ...

2

A volume of water contains a gigantic number of molecules, each with different speeds. The ones with faster speeds are the ones that escape the surface boundary forces to evaporate into the air. Thus the remaining ensemble of water molecules has a lower average speed of movement = lower "temperature".

2

This answer was posted on chemistry.SE by @permeakra: After quick digging I found, that glass cleaner solutions usually contain alcohols and surfactants. This additions reduce surface tension and allows the solution to interact with glass more easily, distributing the solution over the entire surface. The white stripes visible after water dried are ...

2

In glass,there can be different types of staining based on how the stains form http://www.britewayservices.com/resources/HardWaterSpots.pdf Based on your nature of question I think you are talking about limescale staining.Sometimes stains are from due to chemical reaction between silicates and with the calcium and magnesium in hard waters.These minerals ...

2

Heat of vaporization is related to enthalpy change, while dew point is related to free energy change, i.e. enthalpy plus entropy. That's why they are very different concerning relative humidity. The enthalpy of a gas is more-or-less independent of pressure or partial pressure, because gas molecules don't really interact with each other. At insanely-high ...

2

I think you have a misunderstanding of the technical terms vapor pressure, boiling and partial pressure. Vapor pressure or better equilibrium vapor pressure is the pressure at which an equilibrium is reached between evaporation and condensation at the liquid surface. Usually it is a function of liquid temperature. E.g. water has a vapor pressure of about ...

Only top voted, non community-wiki answers of a minimum length are eligible