Hot answers tagged

49

A large amount of water (i.e. if the path of light through it is long) will simply start absorbing light, as it's not completely transparent. For smaller amounts, as when pouring it from one container to another, this is mostly negligible. However, there is also surface reflection. A small amount of the incident light will be reflected off by the surface. ...


49

There is another effect here which is significant, as follows. Warm water wants to evaporate, but in a flask-shaped container, the evaporation can take place only at the free surface of the water in the flask. Furthermore, as soon as the boundary layer of air right next to the warm water becomes saturated with vapor, the diffusion of water vapor into the air ...


47

This is just to add an illustration to noah's and Ralf Kleberhoff's answers which correctly point out that refraction is the main reason. Note that although most of the light rays do make it through the water drop, most of them do not continue on the path with the rest of the light bundle, but end up somewhere else. As a result, right behind the drop, the ...


37

Although there are already some good answers, I'd like to give it another attempt. Water is transparent in the sense that most of the light that enters some volume of water, also exits at the other end (unless we talk about multiple meters of thickness or lots of dirt in the water). But that doesn't mean that it passes water unchanged. Wherever light enters ...


16

Regarding water droplets collecting on the surfaces of your glasses: Those water droplets backscatter the incoming light in random directions, including ones away from your eyes. This means that any glass lens surface populated with water droplets will appear less bright than it would without the droplets, and the random scattering will obliterate anything ...


15

Water in a fluid phase has density of $1.00~\text{g/cm}^3$, while in a solid form (ice) - $0.92~\text{g/cm}^3$. So while freezing water expands in volume (and thus drops in density), it becomes lighter. That's why we see pieces of ice floating in a river. Due to same water anomalous property, deep lake bottoms may never get completely frozen, because liquid ...


14

The restoring force for waves on the surface of water is gravity, is why such waves are called "gravity waves" (not gravitational waves!). Gravity waves on deep water have $$ \omega_{\rm gravity}(k)= \sqrt{{gk}}, $$ which is independent of the density of the water. The restoring force for sound waves in water is the water's elastic properties and $...


8

There are two factors at work here. The first is whether water is "clear", meaning, allows most light to pass through it. And it is, whether it's solid or in a bunch of tiny droplets. The second is whether you can see through it. In order for a substance to be "transparent", it has to have two properties. First, it has to allow a non-...


7

The surface of the water evaporated due to partial pressure. As this transformation from a liquid to a gas state costs energy (the so called latent energy), the remaining water becomes "cold" (decreases its temperature). Thus the more water evaporates per time unit the more ice you obtain. Thus the question is, do you get more gas molecules if the ...


6

The $absolute$ humidity is much lower outside. The lenses of your glasses have some thermal inertia, and while you were outside they got pretty cold. When you step inside, where the absolute humidity is higher, a thin layer of air near the lenses cools to below the dew point, and condensation occurs. Then when you go back outside, the droplets evaporate. ...


6

For a centimeter or so, I wouldn't try to complicate it. Given cold enough temperatures, that depth can freeze solid in a single night. Also, trying to control the layers thinner than that would be difficult. If you needed it much thicker, then the layered approach would help. The problem with putting all the water down at once is that basically all of ...


5

Nothing would happen. You could even cool to $-1 ^\circ$C without a phase change. Then, if nucleated maybe by a bump, a small fraction of the water would crystallise to a solid.


5

The difference is really remarkable, but is similar to the difference of intensity in the sound if we touch the floor or the bucket with our finger. The sudden impact produces a very small downward displacement in the point of contact, that spreads as a mechanical wave. The maths are shown here. In the bucket, the energy is mainly dissipated in vibrations (...


5

I guess some light will get reflected at the interface air-water, which will lower the intensity of light through the stream. That and possibly lens-like phenomena which leads to a non-uniform distribution of light intensity on the other side.


4

The fact that you can see water at all means it's not completely transparent. Since not all the light goes straight through, there will be a shadow.


4

For fastest freezing make sure the rink is shaded during the day, and exposed to the sky at night. Optionally you can add environmental snow or ice to the fill water to reduce the amount of cooling (and the amount of tap water) needed allwing you to build thickness more rapidly. Ice tends to insulate the water below it a bit, so work in layers you'll soon ...


4

Short answer: the acoustic impedance match between the bottom of the bucket and the surrounding air is better than the acoustic impedance match between the floor and air. Sound waves in air are a very non-dense medium moving with large amplitude/distances. Sound waves in the floor are a small amplitude movement of a dense medium. For maximum energy transfer, ...


4

Unless you're pulling hard enough to cause cavitation, which I rather doubt, he's wrong. The primary reason for propulsion is good old action-reaction. You push water backwards; momentum conservation pushes your body forwards. To the extent that water "rushes in" to the displaced area in front of you, that has little to no effect. See the famous ...


3

There is no violation of the second law here -- you're neglecting that a glass of water is an open system. In other words, it interacts with the environment not only via "heat transfer" but also via mass transfer as well. So, while heat is transferred from a "colder/liquid" phase to a "hotter/vapor" phase, the entropy lost by ...


3

But now, if only the most energetic molecules were able to escape the inter-molecular forces and end up as water vapour, does this not mean that the water vapour above the surface now has a higher temperature than that of the water beneath it since the vapour is composed only of the most energetic molecules and the remaining liquid contains only the least ...


3

Absolutely. On a clear, windless, dry night, get one of those IR thermometers and point it up at the sky. Temperatures below -40C can be seen in lots of places if it's dry enough. The less water vapor in the air, the cooler it can appear. The thermal environment for the water is: conduction with the tray (chosen for low conductivity) conduction with the ...


3

Bucket acts as some sort of a drum, where the membrane is resonating up and down. But the floor only squeezes up and down. The bucket has more room for resonating and resonates more than the floor.


2

The main damage here will be caused by the incompressibility of water. (Actually, the relative incompressibility of the water compared to the human body.) The effect would be somewhat similar to a human body entering water at a high speed - the incompressibility of water means it is like concrete. In the case of the falling water-filled elevator, a shock ...


2

Possible but requires very specific circumstances. Suppose we put the same bowl of water on the outside of a space satellite orbiting in the thermosphere and position huge mirrors in nearby orbit to block the radiation of the sun. The near-vacuum atmosphere there is at temperatures above 2000 K (1). The water will never equilibrate to 2000K. The thermosphere ...


2

The Key variable is the Latent heat (Enthalpy) of water evaporation - $L$. Each segment of $dx$ of the paper stays on the hot plate for $t = \frac{20m}{200m/min} = 6s$. In that $6s$ the paper+water heats up to $100^0C$ and the rest of the heat power goes to evaporating it. You still need to figure out the power delivered to the paper (depends on the thermal ...


1

The meaning of "transparent" is that you can see through the object and light can go through it, however, the light can't smoothly pass through the object. It is called Refraction which means that light bends as it goes through water this bending of the light can create a illusion where there may be a shadow BELOW the glass of water but the actual ...


1

In a time $t$ your heater generates an heat $W$ given by $$W=Pt$$ a fraction $x$ of this [I am assuming $x$ is already divided by 100 so it is a number between 0 and 1] i. e. $w=xW$ is adsorbed by water, that is, the heat actually adsorbed by water in a time $t$ is $$w=xW=xPt$$ On the other hand, the heat capacity of water $c$ is 4200 J/Kg/C i.e. for $1kg$ ...


1

Because there are other forces at work in this case besides just gravity- namely, surface tension. If you take that into account, then the water clinging to the side of the tipped glass as it runs down it is, in fact, following the path of least resistance.


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