5
votes
3answers
194 views

Is it faster underwater to go down without air or up with air?

So I had a very interesting conversation between me and my friends about this topic, but we could not find the answer. The Situation Lets say you are in a pool and you want to touch the bottom and ...
7
votes
2answers
85 views

Practical (maybe naive) question on boiling water

I put a glass bottle in a big pot, bottleneck up, I fill both pot and bottle with very hot water. The bottle is submerged except a few cm of the bottleneck and filled to the brim so some water ...
11
votes
3answers
516 views

what is this force that is able to surpass an entire planet's force on it?

I have a wet teabag in an empty cup. If I will hold the teabag and touch the wall of cup with it, it will stick to the cup, like there would be glue or some magnetic field, but there's just water. ...
5
votes
2answers
209 views

Why does evaporation take place? [duplicate]

I was looking at at puddle when I thought that this puddle will evaporate tomorrow but then it occurred to me that the boiling temperature of water (aka to turn into gas) is $100$ degrees under 1 ...
0
votes
1answer
57 views

Why is mud muddy?

How to explain properties of mixture of sand with water? Why is it so coherent and slippery at the same time? Is it due to hydrogen bonds? Why is mud of smaller grains more slippery and incoherent ...
56
votes
7answers
8k views

How does hot water clean better than cold water?

I had a left over coffee cup this morning, and 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 other people ...
10
votes
2answers
349 views

a wierd image of sun

Have you ever notice the sunset's image in the sea? It's like long light path to the end of the horizon! I've attached a sample of this: How can we explain this? I know that it can happen even in ...
5
votes
3answers
5k views

Does wrapping a wet paper towel around a glass bottle really speed up the cooling process?

There are claims like this one that you can improve the cooling speed of beverages when you put them wrapped in a wet paper towel inside the refrigerator/freezer. I've just tried it by myself and ...
42
votes
4answers
3k 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 ...
4
votes
2answers
226 views

Why does my kettle only make a noise when it is turned on

Almost as soon as I turn my kettle on it starts to make the familiar kettle noise, yet very shortly after turning off the power the boiling noise stops and the kettle is totally silent. The ...
5
votes
1answer
55 views

What are circles on broth (eating soup) surface?

Think about broth in the soup, usually it has circles on its surface. What are their properties? Why there are many of them (not a few big blobs)? Are they depended on liquid's temperature? What needs ...
1
vote
2answers
779 views

Why does a bottle shrink when you pour hot water in it?

I think the title says pretty much. Last night I poured hot water in a half full bottle of water and closed the cap. The bottle immediately shrunk. Why? My girlfriend suggested that the hot water has ...
7
votes
3answers
577 views

How does a canvas water bag cool water?

I was reading about this water bottle by Botl that behaves like a canvas water bags to keep water cool. I found out that this idea is an old idea and cars would drive with water bags in front as shown ...
-2
votes
1answer
69 views

What is the physics concept in sponge filter

I really need help I want to ask what is the physics concept in Sponge Filter?
0
votes
2answers
124 views

How do you keep a fridge full of food cooler?

I just graduated and a mate moved into a flat (none of us are physicists by the way). So, were graduates, we got a new flat, and were broke. So, were now having a debate on how to keep a fridge ...
3
votes
2answers
394 views

Would a small puddle of water evaporate faster if you spread a dry towel over it?

Let's say you spill 10ml of water on the kitchen counter. It forms a small puddle that would evaporate after a while (assuming room temperature and sane humidity). Would spreading a large, dry towel ...
25
votes
4answers
4k 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 ...
3
votes
1answer
195 views

Does tapping at the side of a bottle prevent shaken soda from bubbling over?

Anecdotal evidence has it that a bottle of soda that was heavily shaken will not bubble over if tapped at the side multiple times. Yet I wonder: Has the tapping really any effect? Or could it be that ...
8
votes
1answer
429 views

What determines bubble locations in boiling water?

Something a little different to our usual fare. I was boiling a pan of water for cookery the other day, and got to wondering what caused the location of the bubble streams from the bottom of the pan. ...
2
votes
3answers
231 views

Why is there more steam when water is subject to less fire?

When I cook things, such as scallop and salmon, I found that the food may be more tender if I wait till the water boils (at 100 C) and immediately turn the fire lower so that the water is not bubbling ...
15
votes
1answer
689 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 ...
4
votes
1answer
214 views

How would one calculate the amount of water contained in a cloud?

So I was looking out the sky one day and I wondered how I would go about calculating how much water was contained in a cloud. I figured the following simple outline 1) We need to roughly know how big ...
0
votes
2answers
129 views

The Ultimate Hand Dryer

I have come across many hand dryers that attempt to dry your hands really fast after you wash them. Here are two of them: XLERATOR http://www.exceldryer.com/ Dyson Airblade ...
1
vote
1answer
299 views

Why does the water-pressure of my shower fall if I hold the shower head high?

I live in a very old house - build 1902 - in the 4th floor in the city of Karlsruhe (Germany). I have a shower and the gas-heater for the water is in it: If I hold the shower head over some height ...
22
votes
2answers
5k views

Why is boiling water loud, then quiet?

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 ...
3
votes
1answer
292 views

Boiling when I plunge my french press?

Occasionally when I make coffee in my french press I experience something odd. It happens pretty infrequently but certainly enough to be curious about. I have the grounds ready in the carafe. The ...
4
votes
2answers
2k views

Why are refrigerators 4 degrees and freezers -18 degrees?

I assume that the refrigerator's temperature of 4 degrees has something to do with the fact that water is densest at that temperature. Does that inhibit microbe growth? But what about the freezer, ...
0
votes
0answers
2k views

How to determine size of a Heat Exchanger?

I am designing a Tube heat-exchanger, similar to this: My process requires water (at room temperature, 18C ~ 22C) that is being pumped out of a small tank (300 Liters) to be heated in a ...
12
votes
3answers
3k 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 ...