# Tag Info

## Hot answers tagged water

65

Yes. There are three mechanisms of heat loss (this applies generally, not just to the man in this example) radiation, conduction and convection. In most everyday cases radiation can be neglected so we just have conduction and convection. Conduction is just the transfer of heat along a static object. For example if you hold the end of a metal bar in a flame ...

19

The blanket would help a bit in the same way it keeps the body warmer in cold air, by inhibiting convection and allowing an interface of warmer air between the blancet and the body, but water is a better heat conductor than air and it will not be very efficient. Divers who stay long in the water have water suits whose material is designed to keep the body ...

9

What is probably being referred to here indirectly is the fact that air with moisture in it is less dense that dry air. The question becomes, is the buoyancy force of an empty egg with the optimal moisture content of air sufficient to overcome it's weight? Searching around I see that water vapor has a density of 0.804g/Land dry air has a density of 1.27 ...

9

Based on your comment, I think you are indeed asking a more profund question than your teabag suggests: Why is it that gravity is so weak compared to the other forces? The answer is: We don't know. Seriously, that is one of the holy grails: To first find the Grand Unified Theory of nature in which all forces except gravity are explained as coming from one ...

7

Blankets do not "warm you." Blankets slow down heat transfer by convection, by simply restricting the movement of a medium which may carry heat. Air absorbs heat from solid objects by conduction. Air does not conduct that heat to other air molecules very well. So, if you restrict the movement of those air molecules, you will limit the ability of that air to ...

7

To figure out why this happens, you need to think about what boiling is, and how it works. As you would know, the water in the pot boils because its temperature was raised above the boiling point by the flame. This required a net transfer of heat from the flame, through the pot, to the water in the pot. Why did the heat flow in this direction? Because 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 ...

4

To start with, "water freezes faster when it starts out hot" is not terribly precise. There are lots of different experiments you could try, over a huge range of initial conditions, that could all give different results. Wikipedia quotes an article Hot Water Can Freeze Faster Than Cold by Jeng which reviews approaches to the problem up to 2006 and proposes a ...

4

This happens due to cooling affect of evapourisation. As you must be knowing, the temperature of the lquid is a factor of evapourisation. So as the temperature of hot water is more, the rate of evapourisation is also more. Now this is where thwe cooling effect of evapourisation takes place. As the water evapourates, it takes away some heat thus cooling ...

4

Water vapor is invisible. I think you mean fog - fine water droplets condensed from water vapor. Pressurized planes fly with an 8000 foot equivalent altitude and humidity in the cabin is low. But, at 35,000 feet (called Flight Level 35) it is likely one would get a brief fog. If loss of pressure is fast, you would only get to watch for a few seconds. At ...

3

The showers I have used that have two knobs have something akin to a globe valve for each line As you unscrew the handle, there is more opening between the plug and the body, letting more water through. The resistance of valves like this is quite variable when the plug is near the body. Once the plug is withdrawn a certain amount the resistance is small. ...

3

Consider this diagram showing the three columns you describe all connected to the same body of water: Your question asks whether the three pressures $P_1$, $P_2$ and $P_3$ will be the same. The answer is obviously yes, because the columns are all connected to the same body of water. For example if $P_1 > P_2$ then water would flow from the base of ...

3

When you put the ice cubes in, the temperature of the cubes is (much) below freezing temperature. The drink in the glass is above freezing temperature. The interface between the ice and the liquid (the surface of the ice cube) is cooled by the ice cube, but heated by the liquid. The ice cube heats up in this process and the liquid cools down in this process ...

3

I believe that in the top you'll find it's the saturated vapor pressure of water. http://en.wikipedia.org/wiki/Vapour_pressure_of_water (80 F ~27 C vapor pressure of about 27 mmHg or 27mm/760 mm * 14.7 = 0.52 psi.. not bad.

3

Taking an intuitive guess here: The pressure above the water column is indeed very low, and water molecules at the surface may escape - but they are also held back by the surface tension of the water (is your meniscus concave or convex?). There is an equilibrium here, and the temperature is low enough that the water won't boil off all at once. So at room ...

2

The force you describe is a capillary force. The following diagram illustrates where this force comes from: The diagram is supposed to show the thin film of water between the tea back and the wall of the mug. Any air/water interface has a surface tension that makes it behave like an elastic membrane. The air water surface is trying to shrink, and that ...

2

If the flow is laminar, i.e. not turbulent, then the relationship between flow rate and pressure is given by the Hagen–Poiseuille equation: $$\text{Flow rate} = \frac{\pi r^4 (P - P_0)}{8 \eta l}$$ where $r$ is the radius of the pipe or tube, $P_0$ is the fluid pressure at one end of the pipe, $P$ is the fluid pressure at the other end of the pipe, ...

2

Impact on water is a very complex topic. Your simple calculation just figures out the velocity of a free-falling body after a 50 m drop. That just tells you the initial relative velocity of body and water surface. It doesn't tell you much about the force at impact, or whether the person survived. There are two things that might kill on impact: high local ...

2

EDIT: replaced "fluid" with "liquid", thanks to Kyle. I am not aware of any material with a liquid phase in near-vacuum. Probably, the liquid would evaporate and maybe a part of it freezes solid due to evaporation cooling. EDIT: NeuroFuzzy pointed to a youtube video containing an ionic liquid, which is able to retain liquidity in very near vacuum. What ...

2

Look at the phase diagram of water: You can see there is a region where ice and water vapor can coexist. Ice turning to vapor without melting is called sublimation. The energy needed for a water molecule to break the bonds holding the ice together is quite large - so the probability that a thermal fluctuation is big enough for a molecule to escape is ...

2

Solid ice does sublimate (go directly from a solid to a gas) over time, but the process is fairly slow. You can see this simply by leaving ice in your freezer for several days. The ice will gradually sublimate away. Wind and dry air both speed up this process, but it is still nowhere near as fast as evaporation under most circumstances. In Antarctica, ...

2

In short, they are hard to separate because even though the molecules are very different, they have properties that attract them to each other. Water is a polar molecule. the oxygen molecule oxidizes the two hydrogen molecules, creating a positive charge on the hydrogen side, and a negative charge on the oxygen side. Meanwhile, salt is composed of Sodium, ...

2

$"$If we put a crystal of salt in the water, what will happen? Salt is a solid, a crystal, an organized arrangement of "salt atoms." Strictly speaking, the crystal is not made of atoms, but of what we call ions. An ion is an atom which either has a few extra electrons or has lost a few electrons. In a salt crystal we find chlorine ions (chlorine atoms ...

2

Fact: By increasing the air's temperature, one also increases the amount of water vapor it can hold before saturating. Speculation: Therefore, the osmotic pressure on water molecules in your hair increases and the water vaporizes more quickly than with room temperature air.

2

Some of these responses are hilarious, yet some have a bit of accuracy. For the man who asked the question... never believe anything seen on TV. Ever. Have divers been to depths greater than 100m, 200m? Absolutely. Does it require a monumental amount of time, money, planning, and training? You bet. Not just the decompression, but the acclimation to the ...

1

Consider the fluid in the source tank to be of density $\phi$. Let the height of the source tank be $h$ and the length be $l$. Pressure i.e force per unit area exerted by the fluid molecule is directly proportional to the volume of the fluid. Let the opening of the source tank be of diameter $x$ (assume it to be at the bottom most part of the tank) such that ...

1

1: If you have the real estate available, then it is more efficient to have large, shallow ponds. This way you maximize the surface area that is irradiated by the sun. Thus, more heat is transferred to the water. 2: The pond layout you describe seems complex and it would definitely require some level of control. The simplest way is simply to fill the ponds ...

1

If you replace the fluid scenarios with solids with matching have the same shapes, then indeed the pressure at bottom would be the weight of each solid divided by base area, i.e., they would be different! Then what's different about the fluid case? I presume in scenario 1 you have a prism, in scenario 2 you have a bottom-heavy frustum, and in scenario 3 ...

1

No. For the same reason that you can't pick yourself up by your shoelaces. However, if you were to fill a container with water and close off the escaping steam with the eggshell, it would be possible to "levitate" the eggshell with the rising steam.

1

One word really: friction. Surfaces that are "slippery" or difficult to walk on have much smaller coefficients of static and kinetic friction. Static friction is why its hard to get things moving and kinetic friction is what slows things down once they start moving.

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