The motion of fluids (gases, liquids and granular material).
Questions tagged [flow]
1505 questions
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Why does rainwater form moving waves on the ground? Is there a name for this effect?
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 happening. There was nothing uphill actually…
user541686
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Why does water falling slowly from a tap bend inwards?
This is something anyone could easily verify. When we open a tap slowly, water bends inwards (towards the axis) while maintaining its laminar flow. After a certain height below the opening, the flow becomes turbulent. I've approximately illustrated…
Vishnu
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Why does pitch increase when you blow harder into a whistle?
When you play recorder or whistle, the pitch depends on how hard you blow into the tube. E.g. when you blow a whistle, initially the pitch is slightly lower when there is less air flow. This seems counter intuitive since the airflow should only…
39
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Why do you have to blow sideways on a flute?
If you were to play a flute, you would want to blow sideways across it, kind of like a bottle, like in Fig 1. Why would this be better than blowing straight in to the hole, like in Fig 2? It seems like more air would go into the flute, which seems…
Derian
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Why does a weather vane arrow point in the direction of the wind?
It seems that a weather vane will rotate in order to minimize energy and thus orient itself parallel to the wind.
What I do not understand is why it is implied that the weather vane arrow should point in the direction of the wind.
I do not…
user391339
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What is the shape of the upper boundary of water hitting a screen?
When I saw that thing I did not understand how that shape is formed? To be ideal, take a vertical smooth plane. Now aim at the wall with a thin water tube. Then the outer layer forms a "parabolic shape" with stagnation point as focus of it. I found…
Sandesh Goli
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Are there any fluids that flow slower in a constricted region, unlike water?
It is well known that when water flows through a tube you can make it flow faster by making the tube narrow.
Now consider what happens when a group of people are moving and the space becomes narrower. The opposite of what happens with water happens…
Ibraheem Moosa
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Can a fan cause a liquid to cool below room temperature?
I enjoy the occasional hot drink, but place it below a small fan in order to cool it to a drinkable temperature. Unfortunately, as expected, I commonly forget about my drink, and it ends up very cold.
In fact, it ends up so cold that it feels much…
Tim
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Why does a mosquito net block the breeze even though its mostly porous?
When my window is fully open, I can feel the breeze from outside. But when I put on my mosquito net, the breeze gets blocked almost completely. Why does mosquito net block the breeze, even though its mostly porous?
Edit: The net is made up of metal…
AlphaLife
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How is possible for current to flow so fast when charge flows so slow?
How is it possible for current to flow so fast when charge flows so slowly?
We know electrons travel very slowly while current travels at ~the speed of light.
Lay González
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Bernoulli's equation and reference frames
So I was thinking about this while driving home the other day.
I've never been quite clear on why when you drive with the windows down air rushes into your car. I thought this might be explained by Bernoulli's equation for incompressible flow, but I…
PatEugene
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Why is air pressure different between the inside and the outside of my house?
I have two identical barometers. I made sure they were calibrated to each other in the same room. Then, weeks ago, I placed one outside.
Right now, the outside one reads $30^\circ\text{F}$ and $1030\,\text{hPa}$ whereas the inside one reads…
jtolds
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What causes wind gusts?
A difference in temperature causes different pressures, air travel from high to low pressure, and that is wind.
We can even produce wind in an experiment like in this video. In this video, what is the way it can produce gusts?
To increase wind…
22flower
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Can you model cold as flowing?
Obviously, cold isn't a "Thing".
Coldness is the absence of heat, and when you add a cold ice-cube to a drink there are no particles of "coldness" flowing into the rest of the drink cooling it down - the heat of the rest of the drink (in the form of…
Brondahl
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The water analogy seems to imply that power = current. Why is this incorrect?
Many people think of the water analogy to try to explain how electromagnetic energy is delivered to a device in a circuit. Using that analogy, in a DC circuit, one could imagine the power-consuming device is like a water wheel being pushed by the…
lyndon
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