The quantitative study of how fluids (gases and liquids) move.
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1answer
90 views
Water, how do you make ripples
How do I make a ripple effect in a bowl of water. I have tried throwing small pebble sin but it just splashes and sinks. I have read that I need to make the water a thicker liquid ie add glycerine, ...
0
votes
0answers
46 views
Water Stream from a Horizontal Surface
If water was projected from a flat surface where gravity was equal all over the surface. What would happen when the water fell in on itself? The water is in a continuous stream and is perfectly ...
1
vote
3answers
119 views
Unclear how heat interacts with Navier Stokes
I am playing around with an Navier stokes solver and I'm having trouble introducing heat.
Am I right in thinking this would be introduced in the ${\bf f}$ term of ${\partial{\bf u}\over\partial t} = ...
4
votes
0answers
103 views
Can a divider “laminarize” turbulent flow and thus reduce friction?
Looking at the Moody chart I think to myself, the friction factor doesn't decrease much at all with Reynolds number after a certain point. I wonder if laminar flow is more efficient in a sense, and ...
6
votes
3answers
175 views
Why does string not wick down?
I regularly drink tea at work and I often reuse the tea bags (yes I know I'm a cheapskate). Yesterday afternoon I used a tea bag once and kept it in the cup in case I wanted another cup before I ...
9
votes
2answers
304 views
Whistle Physics
I'm looking for a simple explanation of how a whistle operates. I know that forcing air over a sharp lip can set up a wave in a resonating cavity, but how? "Most whistles operate due to a feedback ...
5
votes
1answer
99 views
Measuring acceleration of a bus using water between two sheets of glass
I was riding a bus one day and noticed that the double windows had some water between them. As the bus accelerated, the water collected to the sides, first forming a trapezoid and then a right ...
1
vote
2answers
140 views
continuity equation for a fluid with variable density
I am trying to derive the equation for buoyancy frequency in a stratified fluid and am struggling with some of the equations. I have a limited background in fluid dynamics so I basically just need ...
7
votes
3answers
2k views
How does a hole's size affect the distance that water will squirt
I took a bucket, drilled 2 different sized holes on the side near the bottom and filled it with water. The stream of water the proceeded from the larger hole traveled further than the stream from the ...
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1answer
37 views
When moving something by entrainment in a fluid stream, where does the energy come from?
The particular Something I had in mind here would be air bubbles that are pulled downwards against their buoyancy by a stream of water falling down a shaft. The work required to push those bubbles ...
1
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0answers
43 views
Is sonoluminescence relevant to the behaviour of Navier-Stokes (or converse)?
More precisely, could Sonoluminescence be a singularity of Navier-Stokes(NS)?
Is there some other connection that might be interesting, or is it completely irrelevant?
Wiki page mentions NS, but says ...
2
votes
1answer
60 views
Oscillations of a fluid particle in a stably stratified fluid
Could anyone help me work through the following set of equations:
I found these online at
http://marian.fsik.cvut.cz/~bodnar/PragueSum_2012/Staquet_1-2.pdf
and I'm trying to work through them. I ...
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1answer
125 views
How to calculate pressure field in potential flow
I haven't ever studied fluid dynamics before and may mix something here, so please, be patient :).
Given flow potential of the form (homogeneus flow over a dipole):
$$ \phi = u_\infty x ...
2
votes
1answer
107 views
Sideways motion between a vertical launch from a planet and landing [duplicate]
I saw a video some days ago (Hello Kitty in Space) of a schoolgirl successfully launching a balloon into space which later popped and landed ~47 km from launch site.
If I vertically launch an object ...
16
votes
3answers
1k views
Why does the sound pitch increase on every consecutive tick at the bottom of a filled cup of coffee?
Since I don't know the proper physical terms for this, I describe it in everyday English. The following has kept me wondering for quite some time and so far I haven't found a reasonable explanation.
...
1
vote
1answer
127 views
How fast does water fall in the middle of a very very thick waterfall?
Let me create a very artificial experimental set up. Take a bathtub the size of Delaware and suspend it a mile above the ground. Fill it with water (though I'm not sure to what depth - and it might ...
6
votes
2answers
333 views
Surface tension of solutions and mixtures
The inspiration for this question is over on cooking.stackexchange, asking more about actual measurements for commonly consumed liquids, but I'm interested more generally as well.
What determines the ...
2
votes
1answer
168 views
Water vs Milkshake being sucked through a straw
Consider water in a glass being sucked through a straw. The water rises up in the straw because of a pressure gradient introduced by the sucking action.
Now, change the liquid from water to something ...
3
votes
2answers
288 views
Low pressure, pulsating, series of water droplets
I want to create a stream of water that emits only a droplet of water, waits a few milliseconds, and then continues. The important thing is that I need to create a visible gap between drops.
...
13
votes
2answers
440 views
What causes ballpoint pens to write intermittently?
After a while, a ball point pen doesn't write very well anymore. It will write for a little distance, then leave a gap, then maybe write in little streaks, then maybe write properly again. It seems ...
7
votes
2answers
381 views
What is enstrophy?
In turbulence, the enstrophy of a flow in a domain $\mathcal{D} \subset \mathbb{R}^{D}$
$$
\mathcal{E} = \int_{\mathcal{D}} |\vec{\nabla} \times \, \vec{v}|^2 d^{D}x
$$
appears sometimes, it's cool ...
3
votes
2answers
192 views
Need help understanding dynamic and static contact angles
I've run into a conceptual road block. I'm coming to you guys because I think my adviser is getting annoyed with me. The concept involves a meniscus being pulled up a cylinder. I understand that ...
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vote
1answer
1k views
“Troll physics”: Buoyancy for infinite power [duplicate]
Possible Duplicate:
What is the fallacy in this infinite motion machine?
Most of the "troll physics" images I can figure out, but this one has me stumped. What is broken about the following ...
3
votes
1answer
166 views
How to estimate the Kolmogorov length scale
My understanding of Kolmogorov scales doesn't really go beyond this poem:
Big whirls have little whirls that feed on their velocity, and little whirls have lesser whirls and so on to viscosity. ...
12
votes
2answers
121 views
Cascade in relativistic turbulence
The Kolmogorov theory of turbulence indicates an energy cascade in turbulence. Is there a corresponding version of relativistic fluid?
4
votes
2answers
227 views
Why do cars gain lift while going at a high speed?
I've been researching the physics involved with spoilers and I've just been turning up the same information about spoilers giving the back wheels of a car more traction by acting as an up side down ...
1
vote
1answer
78 views
Satellite droplets in a breaking liquid jet
The famous example of a dripping faucet is an example of a Rayleigh-Plateau instability in which there is a certain jet radius below which perturbations on the surface will grow to break the jet into ...
7
votes
5answers
314 views
Zigzag flow of water along a vertical glass window
I've observed this behavior many times. When it rains, the rainwater will form vertical channels along a glass window. The flow of water is mostly confined within these vertical channels and the ...
1
vote
1answer
148 views
Surface Tension of a Liquid - When a liquid body is acclerating
As far as I understand it (which admittedly isn't very far), surface tension forces are made up by the tension-attractive forces of molecules at the liquid-gas/vacuum interface, such as those between ...
-1
votes
2answers
146 views
A simple logical problem regarding pressure and force
Suppose a 2 meter long pipe, with area of cross section is $1 m^2$. The pipe is vertically placed, with the bottom end closed. Inside the pipe, at the closed bottom end, there is $1 m^3$ of air, ...
0
votes
2answers
148 views
Train motion… Push or Pull?
While arguing against my friend today about the turbulence appearing between train's wheels. I told that the train pushes air aside during its motion through the tracks. But, he rejected it. Then, ...
4
votes
2answers
58 views
How does the correlation length of weather emerge?
The question is pretty simple: If I know the weather where I stand, I can estimate the weather 5 meters or 1 km away away pretty well, but I'll have a hard time guessing what the weather is, say, 50 ...
7
votes
2answers
117 views
Could motives aid in the study of the Navier-Stokes equations?
Recently, mathematicians and theoretical physicists have been studying Quantum Field Theory (and renormalization in particular) by means of abstract geometrical objects called motives. Amongst these ...
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1answer
142 views
Best way to move teaspoon to dissolve sugar in a cup of tea
I know that there is asked questions about something like cooling down cope of coffee..etc, but this one is little different.
My friend was watching TV program of English eating etiquette, and they ...
2
votes
0answers
59 views
Fluid flow in a hollow spring(helix)
Liquid flowing in a long hollow spring(helix). Any effects on the flow rate etc when the spring is stretched or compressed?
When the stretching or compressing of spring is done at brisk speeds the ...
1
vote
1answer
118 views
Can silicon droplets bouncing on a vibrating surface be a model for Quantum Mechanics?
In
this video on
youtube
it is claimed that silicon droplets bouncing on a vibrating surface show behaviour in analogy to particle/wave duality in Quantum Mechanics.
Is this true? Did they ...
3
votes
3answers
1k views
What is the physical meaning of diffusion coefficient?
In Fick's first law, the diffusion coefficient is velocity, but I do not understand the two-dimensional concept of this velocity. Imagine that solutes are diffusing from one side of a tube to another ...
2
votes
2answers
141 views
Can wind blowing on smooth water create speckle interference patterns?
On a calm smooth lake, or even a large rain puddle, I've seen transient rough patches on the surface suddenly appear and disappear, and sometimes move across the water some distance before ...
6
votes
2answers
136 views
Where can I check a solution to 3D Navier Stokes?
A few years ago I developed a solution to the Navier-Stokes equations and as of yet have not been able to locate a similar version of the solution. I would like to know if anyone has seen a solution ...
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vote
2answers
150 views
Finding an equation relating the mass of a blade of a wind turbine to its velocity
I'm writing up my physics coursework and I thought I'd try and find an equation described in the title. This is my attempt:
Is it correct?
3
votes
1answer
293 views
What is the formula for the glug point?
When you pour water out of a bottle, normally you have a smooth stream. However, if you pour it too fast it glugs, which is to say, comes out in quantized bursts. What is the formula for calculating ...
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votes
1answer
282 views
Lamb-Chaplygin dipole
There is an interesting issue of hydrodynamics: whirlpools.
I want to learn about the Lamb-Chaplygin dipole.
Lamb-Chaplygin dipole corresponds to a steady solution of the two dimensional Euler ...
1
vote
1answer
106 views
Swimming and forces
I was told that the total integral of the stress over the surface of a swimmer (i.e. the total force exerted by the swimmer on the fluid) always vanishes, because there are no external forces applied ...
3
votes
1answer
69 views
General parameters of the stress energy tensor in local inertial frame
A general 4x4 symmetric tensor has 10 independent components. How many components are we free to prescribe in the local inertial frame?
For example, relativistic dust is $\mbox{diag}(\rho c^2, 0, 0, ...
3
votes
0answers
52 views
Sound level of organ pipe driven by helium
The sound pressure level of an organ pipe is a function of the gas flow rate delivered to the pipe. Source
Would the sound level of an organ pipe driven by helium be lower than that of a pipe driven ...
3
votes
2answers
303 views
Why water is not superfluid?
My question is in the title. I do not really understand why water is not a superfluid. Maybe I make a mistake but the fact that water is not suprfluid comes from the fact that the elementary ...
2
votes
2answers
225 views
Will the siphoning effect help a system pump water upwards if the water's entry and exit points are at the same height?
I am looking to pump water from a pool up to a roof for solar heating (black plastic tubing) and then back into the pool with the original source water. Does the gravitational force of the water ...
2
votes
0answers
76 views
Stat mech explanation for separation of one liquid from another in gravity?
If one mixes two distinct ideal gases above the Earth's surface, one with a higher molecular mass than the other, then at equilibrium, their number density gradients will be such that at low heights, ...
3
votes
4answers
341 views
Why does smoke go out the window of the car - and what if there's wind blowing instead of the car moving?
When driving a car while smoking with the window open (safety and legal issues aside), I've noticed that the smoke tends to go outside the window.
Why does the smoke go outside?
If the car is ...
1
vote
1answer
45 views
Disregarding drag force that affects pop-up lightweight ball
Is it possible to disregard drag force of water with no viscosity that affects lightweight pop-up ball (its weight is assumed to be zero)? There is a discussion, on which I consider that although ...
