# Questions tagged [fluid-dynamics]

The quantitative study of how fluids (gases and liquids) move.

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### What are some good books on fluid mechanics for the olympiad?

I have already checked out Book Recommendations on the community wiki, but the recommendations there don't suit what I ask for. I need problems/problems+theory book(s) on high-school-physics-olympiad/...
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### Relationship between bridge pylon and water flow

Recently, I was met with the following question: When observing water flow around a bridge pylon, of the following statements, which one(s) are true: a) The bridge pylon applies force to ...
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### Diver's air torus rising from 10m underwater (edited)

[Edit: earlier version was even more messy] I just watched a video of a jellyfish caught in a diver's 'air ring' - a torus blown for the sake of watching it rise. The jellyfish gets drawn into the ...
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### Is the force due to mass flow proportional to the square of the mass velocity?

I'm trying to calculate the force on a surface due to some flow of water against that surface- for simplicity, assume that the mass flow vector is orthogonal to the surface. Using dimensional ...
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### Uranus: The Spin

In his prog. , on the outer planets, Brian Cox stated that Uranus spins on its side because it once endured an interplanetary collision. Such a cataclysm would normally be devastating for both ...
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### Entropy in non-homogeneous equilibrium states and local thermodynamic equilibrium

My question concerns the possibility of using the hypothesis of local thermodynamic equilibrium for calculate the entropy of a non-homogeneous equilibrium states. For example, let's imagine the ...
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### Are conservation of mass and conservation of energy *independent* constraints for physical systems?

I'm modeling fluid systems and want to use conservation of mass (aka 'continuity') and conservation of energy as constraints to help solve for certain system parameters. But it occurred to me that the ...
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### The physics of the startup of a lava lamp

I noticed a strange phenomenon observing a lava lamp. We all know the complex flow of bubbles when the lamp is "hot" and running, but I would like to have some explanation about the startup behavior ...
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### Viscous Force On A Rotating Cylinder

In this question asked in Irodov, it is taken that the friction force acting on a unit area of a cylindrical surface of radius $r$ is given by $Ļ = Ī·r(āĻ/ār)$. A fluid with viscosity $Ī·$ fills the ...
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### Does a thickness of a bubble become constant over time?

Assuming no gravity, imagine you have a bubble floating in the air, does its thickness have a tendency to become constant? State a bit differently, if we start with a bubble with variable thickness, ...
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### Can you explain the perfume bottle with the Bernoulli effect?

Someone explained the perfume bottle with the Bernoulli effect: squeezing the bulb over the fluid creates a low pressure area due to the higher speed of the air, which subsequently draws the fluid up. ...
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### Is there a physical circumstance where the flow of a system changes from a nodal source/sink to a saddle?

Phase portraits for sinks can often like eddies in water, so I would assume there is some fluid or aerodynamic system where these curves appear. But, the only difference between a saddle and a nodal ...
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### Does tilting a liquid develop shear stress on its surfaces?

Please help me these confusions I have. If I tilt a cuboidal container containing an ideal fluid (non viscous liquid), does a shear stress develop on the liquid due to some shearing force acting ...
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### Bernoulli equation

Can we apply Bernoulli equation to a closed system the same way we apply it to an open system? In an open system increasing the speed of the fluid implies that either the pressure or GPE should ...
321 views

### What is the maximum gap that water won't pass through for hydrophobic surfaces?

If I had 2 hydrophobic surfaces (in this particular case, 2 sheets of coated glass), placed edge-to-edge, what is the maximum gap between the sheets where water would not drip between the sheets? Is ...
116 views

### How to scale up a boat design?

I've been trying to research how to scale up a boat design. Specifically I am trying to find out how much power will be needed to "drive" the boat? Suppose I know that a 250 mm model boat, with 100 W ...