Questions tagged [water]

Two Hydrogen atoms covalently bonded to one Oxygen atom. One of the more common compounds on the surface of the earth.

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197
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3answers
48k views

Surviving under water in air bubble

An incredible news story today is about a man who survived for two days at the bottom of the sea (~30 m deep) in a capsized boat, in an air bubble that formed in a corner of the boat. He was ...
195
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1answer
16k views

Strange ice found in my garden

This morning I found a really strange ice formation in my garden. I can't figure out how it appeared, because there was nothing above. The night was particularly cold (Belgium). To give an idea, it ...
98
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6answers
21k views

Why is oil a better lubricant than water?

How come mineral oil is a better lubricant than water, even though water has a lower viscosity? When two surfaces slide over each other with a gap filled with a fluid, the different layers of the ...
90
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8answers
47k views

Why does hot water clean better than cold water?

I had a left over coffee cup this morning, and I tried to wash it out. I realized I always instinctively use hot water to clean things, as it seems to work better. A Google search showed that other ...
84
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4answers
5k views

Why does rainwater form moving waves on the ground? Is there a name for this effect? [duplicate]

A while ago it was raining and I noticed that, on sloped pavement, water was flowing in very regular consistent periodic waves, as you see below. However, I realized I had no idea why this should be ...
81
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4answers
7k views

Why doesn't water actually perfectly wet glass?

According to many high school textbook sources, water perfectly wets glass. That is, the adhesion between water and glass is so strong that it is energetically favorable for a drop of water on glass ...
80
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6answers
20k views

Why does water stop boiling immediately after turning off the heat?

When I am heating water on a gas stove, it begins to boil after some time and bubbles of air can be seen escaping out. However, as soon as I increase the amount of heat in the stove, the rate of ...
76
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1answer
7k views

Why does soaking a fabric make it more transparent?

It's a well-known fact that when one soaks a thin piece of fabric, it will often become more transparent than it was before. What is the reason behind this? I can't put glass behind the fabric and ...
69
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7answers
19k views

When I boil a kettle, what stops all the water from turning (exploding!) in to steam in one go once it reaches 100°C?

While making a cup of tea in the office kitchen, a colleague asked me this question and neither of us could answer with any certainty. We're guessing it has something to do with the pressure of the ...
67
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5answers
21k views

Why is water clear?

Water appears transparent to visible light, yet most other objects are opaque. Why is that? Is there an explanation why water appears transparent? Is water transparent at all wavelengths, or are ...
66
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3answers
6k views

Why does a lot of water vapour come suddenly after the heat source of boiling water is removed? [duplicate]

I have noticed this several times. When I am boiling water, a few seconds before its boiling point, vapours are formed as usual. But if I turn the gas off before boiling, the moment it turns off, I ...
66
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3answers
3k views

What causes insects to cast large shadows from where their feet are?

I recently stumbled upon this interesting image of a wasp, floating on water: Assuming this isn't photoshopped, I have a couple of questions: Why do you see its image like that (what's the physical ...
62
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4answers
278k views

How does water evaporate if it doesn't boil?

When the sun is out after a rain, I can see what appears to be steam rising off a wooden bridge nearby. I'm pretty sure this is water turning into a gas. However, I thought water had to reach 100 ...
60
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8answers
8k views

Will a blanket warm you if you are underwater?

Suppose a man falls into very cold water and gets their foot stuck under a heavy rock. Fortunately, his head is above water and someone is able to call for help. The paramedics want to keep him warm ...
56
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6answers
22k views

If water is not a good conductor, why are we advised to avoid water near electricity (no wet hands near circuits etc.)?

How can water be a medium to conduct current while its ionisation is so negligible that, in principle, no current should flow?
55
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8answers
93k views

Why does ice melting not change the water level in a container?

I have read the explanation for this in several textbooks, but I am struggling to understand it via Archimedes' principle. If someone can clarify with a diagram or something so I can understand or a ...
53
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3answers
25k views

Why is boiling water loud, then quiet? [duplicate]

Water in my electric kettle makes the most noise sixty to ninety seconds before the water comes to a full boil. I have been fooled many times by the noisy kettle, only to discover that the water was ...
51
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6answers
95k views

Why is jumping into water from high altitude fatal?

If I jump from an airplane straight positioned upright into the ocean, why is it the same as jumping straight on the ground? Water is a liquid as opposed to the ground, so I would expect that by ...
50
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3answers
19k views

Why is ice made from boiled water clear?

A common trick to make clear water ice is to boil pure water prior to freezing it. Why does that work and what are the white inclusions in ice that was made from unboiled tap water?
47
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4answers
6k views

Being in a solid state, why is ice slippery? [duplicate]

Saying that ice is slippery is like saying that water is wet -- it's something we've known for as long as we can be said to have known anything. Presumably, humans as a species knew ice was slippery ...
45
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4answers
5k views

Why is water evaporated from the ocean not salty?

I am wondering about this. When salty water in the ocean evaporates we are getting the clean distilled water. Why is that? I was trying to think on this and maybe the comparative size/mass of water ...
40
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4answers
3k views

What is the status of Mpemba effect investigations?

There is this puzzling thing that is called Mpemba effect: paradoxically, warm (35°C) water freezes faster than cold (5°C) water. As a physisist, I've been asked about it several times already. And I ...
38
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2answers
16k views

What happens when you put water under intense pressure?

Pretend you have an indestructible tube that cannot leak, inside which is water. Imagine that in each side of the tube, you have very powerful pistons What would happen if you compress the water ...
37
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1answer
11k views

Was Titanic's captain's decision correct?

I just saw a documentary on Titanic. Someone in that documentary told Captain Smith "Shall we close the water tight doors, sir?" and the Captain replied "No, let it be open. Let the water be ...
36
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2answers
20k views

Before a once-warm lake starts to freeze, must its temperature be 4°C throughout at some point?

This is a problem I just started puzzling over, and I felt this would be a good forum to check my reasoning. So here are the relevant observations followed by my question: Water achieves its maximum ...
35
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3answers
5k views

Why does a blackboard dry very quickly?

When you have made some stupid mistakes on a blackboard, you quickly want to erase it with a wet sponge before anyone sees them. So you clean the blackboard and within a minute the blackboard is clean ...
34
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7answers
8k views

Is it possible to “cook” pasta at room temperature with low enough pressure?

It is known fact, that boiling point of water decreases by decreasing of pressure. So there is a pressure at which water boils at room temperature. Would it be possible to cook e.g. pasta at room ...
34
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3answers
8k views

Why does snow stay after a snowfall?

I have just experienced a snowfall and I am not so clear on how it works. Three days after a short day of snowfall, and having 2 min | 17 max degrees Celsius, full sunny scarcely cloudy each day, ...
34
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4answers
8k views

Why does water rise through a hole in ice

I've just been watching a doco where some guys cut a hole in a frozen lake, the ice is 3 feet thick, I was surprised that the water rose to the level of the ice. My friend assures me it's because ...
34
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4answers
11k views

Why does water have no color?

When a substance absorbs and reflects light, it shows the color of that absorbed and reflected light. But water is colorless. Does it absorb and reflect light. What is the reason for this?
34
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9answers
116k views

How can water evaporate at room temperature? [duplicate]

Boiling point of water is 100 degree Celsius. The temperature at which water in liquid form is converted into gaseous form. Then how it possible for water to evaporate at room temperature?
34
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3answers
2k views

What is the reason for this pattern of noise in electric kettles?

It always seemed to me that the noise from electric kettles follows a pattern: It starts low, then increases, and decreases again before the water starts to boil. To verify this, I performed a little ...
33
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6answers
35k views

Why does wet skin sunburn faster?

There is a popular belief that wet skin burns or tans faster. However, I've never heard a believable explanation of why this happens. The best explanation I've heard is that the water droplets on the ...
32
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1answer
2k views

Can one determine the speed of the rain from the shape of the rainbow?

I was watching the rainbow today and started thinking about the effects of the rain falling in different directions. The idea I had was that normally we model rain drops as small spheres, and this ...
31
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5answers
8k views

How are water vapors not visible?

This site says that water vapor isn't visible. However, take a look at this picture: Isn't that water vapor?
31
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3answers
61k views

Why does water pouring from a glass sometimes travel down the side of the glass?

If you have a glass of water, say, three quarters full and you pour it at an angle of say, $45^{\circ}$ with respect to the the table, the water comes out of the glass and goes directly down towards ...
31
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4answers
15k views

Why does boiling water in the microwave make a cup of tea go weird?

When I boil water in the kettle, it makes a nice cup of tea. Sometimes I need to use a microwave because a kettle isn't available. I boil the water in the mug and it looks pretty normal, but when I ...
30
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4answers
4k views

Lengthwise or widthwise. Which towel will dry faster?

So I was putting towels on drying rack and I had extra space. Should I hang towels lengthwise to speed up drying? If we have a standard, rectangular towel. Say like this: Which will dry sooner? ...
30
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7answers
40k views

Why do tsunami waves begin with the water flowing away from shore?

A sign of a tsunami is that the water rushes away from the shore, then comes back to higher levels. It seems that waves should be both + and - polarized and that some tsunamis should go in the ...
30
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3answers
16k views

Why is there more steam after a pot of water *stops* boiling?

I have a pot of vigorously boiling water on a gas stove. There's some steam, but not alot. When I turn off the gas, the boiling immediately subsides, and a huge waft of steam comes out. This is ...
28
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3answers
7k views

Why doesn't rain fall down in streams (as opposed to drops)

Why is it that raindrops don't collide and 'stick together' on their descent to Earth, arriving in streams rather than separate drops?
28
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3answers
45k views

Why does the water rise?

It's a very popular experiment (eg), from elementary school : put a burning candle on a dish filled with water, cover the candle with an inverted glass: after a little while, the candle flame goes ...
27
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1answer
3k views

Why does a water drop on a hot plate at 150°C evaporate faster than on a plate at 200°C?

I recently read that: A drop of water landing on a hot plate at 150°C (300°F) evaporates in a few seconds. A drop of water landing on a hot plate at 200°C (400°F) survives a whole minute. How ...
27
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2answers
8k views

When a drop of water falls into water, where do the splashes come from?

When a drop of water falls into a reservoir of water from a high enough altitude, water droplets will splash (image credit): My question: Does the water in those droplets come from the original drop ...
27
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6answers
9k views

Why are snowflakes symmetrical?

The title says it all. Why are snowflakes symmetrical in shape and not a mush of ice? Is it a property of water freezing or what? Does anyone care to explain it to me? I'm intrigued by this and ...
26
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5answers
14k views

Eyes open under water

Yesterday I looked underwater with my eyes open (and no goggles) and I realized I can't see anything clearly. Everything looks very, very blurry. My guess is that the eye needs direct contact with air ...
25
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5answers
239k views

Jumping into water

Two questions: Assuming you dive head first or fall straight with your legs first, what is the maximal height you can jump into water from and not get hurt? In other words, an H meter fall into water ...
25
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4answers
3k views

Why is boiling water the second time more quiet than boiling it the first time?

First of all: This is a different question than Why is boiling water loud, then quiet?, although the answers might be similar. When I wake up, I boil some water for a cup of tea. It happens quite ...
24
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8answers
20k views

Will a bathtub full of water weigh more if I add something that floats in the water?

Let's say I have a bucket or something bigger, like a bathtub full of water. I weigh that bath and get some value, $x$. Then I add a small boat made of wood to that bathtub that doesn't touch the ...
24
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4answers
1k views

Why is lightning more rare during snow storms than rain storms?

Lightning and thunder during a snow storm is uncommon. As far as I know, more uncommon than during a typical rain storm. Why is this? I speculate it might be one, or both, of the following two ...