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

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How can a droplet of liquid float on the surface of the same liquid?

This can happen during the rain, or when pouring water. Sometimes small (1-2 mm) droplets of water float on the surface for some time (a few seconds) before coalescing with the big body of water. A ...
2
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1answer
365 views

Flow rate through hole at bottom of tank, estimate time for depth to reach 1 foot [closed]

I am a structural engineering student and have limited experience in fluid dynamics. I'm not quite sure if I'm going about the problem in the correct way. The question is: An open cylinder of ...
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3answers
371 views

Kinematic Viscosity

How would you define kinematic viscosity? What does it physically represent? Around the Internet I've found it defined as just a ratio, and that's it. I saw in an answer that I can think of it as ...
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3answers
379 views

Ideal, isotropic fluid and stress tensor

An ideal fluid is the one which cannot support any shearing stress. It also doesn't have viscosity. My question is what does it mean by a fluid to be isotropic? Is an ideal fluid necessarily isotropic ...
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2answers
218 views

Difference between adsorption and condensation

So I just stumbled across the Wikipedia article on adsorption - and I asked myself, if there is a difference between (physical) adsorption and condensation on a surface? When I look at the water ...
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2answers
59 views

Separating atoms in water

Suppose I have the power of Jean's (X-Men). If I separate the all the atoms in the water in a water bottle, would the volume remain the same?
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2k views

Water VS Soapy Water

I recently did an experiment. I have a cup of tap water, and a cup of tap water mixed with soap. I used an eyedropper to slowly drip drops of tap water onto a penny. Then I cleaned the penny, and ...
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51 views

What's the relation between the type (Gender) of a balloon and its internal pressure

I'm working on a project about balloons and I need to know the relation between the gender of the balloon and its internal pressure. As far as I know, there are some parameters such as " Elasticity of ...
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1answer
53 views

Is the buoyant force on an object is the reaction force?

Is the buoyant force on an object is the reaction force for the force exerted by the objects on the fluid (newtons third law)? Or there are two sets of action reaction force? (objects force and ...
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167 views

Calculating saturation mixing ratio for water in air

If I have air pressure (in, say, Pa) and air temperature (in, say, K) - how do I calculate the saturation mixing ratio for water? I can't seem to find it anywhere and it's a fairly useful quantity to ...
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1answer
49 views

When is it appropriate to drop pressure terms when applying conservation of momentum to a fluid?

I'm trying to wrap my head around pressure forces in incompressible, irrotational, invicid flow. Applying conservation of momentum to a control volume gives me \begin{equation} ...
2
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1answer
515 views

Equilibrium between two water tanks

I've been reading about hydrostatic theory, however I couldn't find a similar case/exercise about my basic problem. I have two water tanks (same size) filled with different water heights, and ...
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1answer
220 views

Find the discharge Q. Pipe flows [closed]

Trying to work my way through an example in my course notes on fluid flow in pipes and I'm really stuck on where to start. The question is as follows; A pipeline 10km long and 300mm diameter with a ...
0
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1answer
47 views

Water adhesion problem

I have a bunch of plastic capillaries that come from two different production lots. I dip them into saline solution and in the capillaries coming from the first lot the solution "mounts" a bit along ...
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1answer
351 views

The velocity of the flowing coming out of the balloons?

Last day , when i was working on two interconnected balloons , a question was kicking my brains !!! This is the explanation of the question: First , suppose a system that composed of two spherical ...
2
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1answer
310 views

Finding turbulent velocity Fourier mode amplitudes from kinetic energy spectrum

A random vector field, such as a turbulent flow, can be decomposed into Fourier modes. Taking a snapshot in time (say an initial condition) we have that the randomly fluctuating component of the flow ...
0
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1answer
208 views

Fluids in a U-shaped Tube

One of the users asked a question about the Fluids in U-shaped Tube. I was wondering and I tried to imagine that the membrane is fixed and the left side is filled up until $h_1=h_2$. So my question is ...
3
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2answers
120 views

Why is an airplane able to increase thrust without moving?

I was just watching some documentaries and saw planes building up power in the turbines without moving. I thought about it and remembered, that this happens before every take off. So, why is this ...
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2answers
435 views

Fluids in U-shaped Tube

In a U-shaped tube, water and oil are separated by a movable membrane. What is the ratio of the heights $\frac{h1}{h2}$ (density of the oil $ρ_{oil}$ = 0.92 $\frac{g}{cm^3}$)? I tried solving by ...
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3answers
319 views

How does vasoconstriction/vasodilation of arterioles change blood pressure?

Background: I am coming at this question from an electrical engineering background, and I feel like I am missing certain assumptions that are going into the statement found in my physiology textbook, ...
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1answer
129 views

Stagnation Point around Sharp Corner

I am trying to design a water-channel that travels through a metal block shaped like a square to cool it down (so it is a 2D problem). One consideration is the wetted surface area, which allows more ...
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0answers
65 views

Solve unsteady-state pressure-falloff axial gas flow equation for permeability

Equation 17 in Section 6.2.1.2 of American Petroleum Institute Recommended Practices 40 for Core Analysis gives a permeability equation of: $$ ...
7
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1answer
235 views

Helicopter, Tricopter, Quadccopter - what's really happening here? Are there generalized advantages on a small scale?

There have been, it seems, a proliferation of quad-copters commercially available. Amazon seriously tried to use them for deliveries. (Search Drone on their website.) The NFL uses one for cameras. ...
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2answers
1k views

Velocity with respect to time in Torricelli's Law

I am having a bit of difficulty establishing the efflux velocity of an open tank of water in terms of time, i.e. $u(t)$, according to Torricelli's law. I know that for a known height $h$ (where $h = ...
3
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1answer
139 views

Is it possible to generate one half of a Karman Vortex Street?

The Karman Vortex Street is a type of phenomenon which is generally illustrated by examples in which a long, solid, smooth circular cylinder moves at constant velocity through a fluid. The long axis ...
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0answers
129 views

Basic fluid mechanics question on the FME

Ok, so I've got a question on a basic fluid dynamics question regarding the force-momentum equation (I don't know how common that phrase is, it's the one used in the textbook I have, but basically the ...
4
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1answer
503 views

How does a hollow-point bullet move smoothly through the air, presenting a 'cup-shaped' nose instead of an actual sharp-point to the fluid?

Hollow-point rounds move smoothly through the air when presenting a 'hollow cup-shape' instead of a traditional 'sharp point' to the fluid air. Does this mean the air trapped, and at some assumed ...
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0answers
105 views

How can we theoretically calculate the number of balloons needed to stop a bullet?

After watching this video, I am interested in proving it mathematically. The problem is that how can we apply the conservation of momentum here to find the velocity of the bullet while we don't know ...
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1answer
156 views

How size of objects lifted by the wind depends on the speed of the wind?

What are the sizes of the objects that could be picked up and flown by tornados, depending on the tornado's speed? To put it another way, assuming turbulent flow and object density much higher than ...
0
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1answer
234 views

Problem regarding Archimedes Principle [closed]

A small amount of mercury is filled into massless cylindrical test tube with an even bottom and length $l=0,200m$. The test tube is put into a large swimming pool filled with water. a) How ...
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2answers
377 views

Why can we produce a sound by blowing across a blade of grass, a paper strip or similar

I just don't know how is the sound produced? Does it come from the vibration of the blade of grass or the air in the up and down?
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2answers
171 views

Foam patterns on espresso

When just prepared, an espresso has a thin layer of foam, known as crema, on its surface. As I move my drink from the bar to a table, the motion destroys the homogeneity of the layer, but I've noticed ...
0
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1answer
84 views

Properties of Fluids-theoritical confusion

I am having a very basic confusion on how we calculate the height of atmosphere when we assume that the density does not change with altitude(density remains 1.29 kg/m$^3$). I want to know why we say ...
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99 views

The name of effect of liquid flow inducing flow to neighboring layers of liquid?

How do you call an effect, when liquid or gas stream is involving the neighboring layers of matter also move? Like on videos of rocket engines testing, when exhausting gas sucks an air and steam from ...
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32 views

Ripples of flowing water on a smooth road surface [duplicate]

Yesterday some friends and I were walking in the rain. We noticed that, on a smooth tarmac road surface, the sheet of water flowing down the road was forming ripples as it went. Why was it doing ...
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1answer
770 views

What is the differential equation for pressure in a container with an orifice?

I've seen similar problems all over physics.SE and other sites. Most of the time it is about non-compressible fluids, or not about the differential equations. The physical system of interest is ...
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2answers
2k views

Is viscosity a function of density only?

I know viscosity is also a function of temperature, but (excluding superfluids) are there any fluids which are less viscous than fluids at lower densities? Is density the ultimate control on ...
3
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2answers
800 views

What air pressure is needed on mars, to have fluid water?

The atmospheric pressure on the Martian surface averages 600 pascals (0.087 psi), about 0.6% of Earth's mean sea level pressure. There is a lot of frozen ice on mars, but it can't melt, because of ...
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1answer
399 views

The Bernoulli equation: positive and negative sign problem

According to bernoulli equation $$ P_1+1/2 \rho v_1^2+ \gamma h_1= P_2+1/2 \rho v_2^2+ \gamma h_2. $$ Because $$ v_1=0\quad h_1=0 $$ So $$ 0= 1/2 \rho V^2+ \gamma h. $$ It is wrong I know, but ...
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2answers
120 views

Hydrodynamics: Conservation of momentum violated by a fan in a cylinder?

Consider the following situation: there is a hollow cylinder with both caps removed. The cylinder is submerged into water. Inside the cylinder, we place a fan (or pump) that pumps the water through ...
3
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1answer
907 views

Why are mass flow rates found using Venturi meter and pitot tube different?

Regarding an experiment to find the mass flow rate of a fluid (air) using a venturi meter and a pitot tube: What could be the cause of a variance in results obtained using the 2 instruments mentioned? ...
9
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2answers
295 views

Explanation of the waves on the water planet in the movie Interstellar?

We will ignore some of the more obvious issues with the movie and assume all other things are consistent to have fun with some of these questions. Simple [hopefully] Pre-questions: 1) If the water ...
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1answer
274 views

How does a faucet work? [closed]

Well I mean how exactly water flows to the sink. How is it pulled through the faucet?
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615 views

How can one calculate diffusion velocity given the diffusion coefficient?

I am creating a basic simulation of 2-D diffusion and was wondering how diffusion velocity of a particle can be calculated if the diffusion coefficient is known (using no other information). Is this ...
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2answers
2k 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 ...
3
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3answers
423 views

Why do square shaped cups spill easier than round cups?

I've noticed that when I use a cup that is square shaped with convex sides, it spills more easily than a circular cup. Why does this happen? What is the most spill-prone cup shape? What is the most ...
9
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3answers
1k views

Would a perfectly clean and perfectly smooth champagne glass have no bubbles?

My understanding is that nucleation sites for bubbles in a champagne glass are either due to defects in the glass or due to fibers in the glass. (See this article for details on that statement.) Does ...
2
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1answer
176 views

How does a sonic black hole (or dumb hole) work?

I came across this term and I heard they used sonic black holes to detect something analogous to hawking radiation, but I have failed to find sources which explain how exactly they work and how they ...
2
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1answer
208 views

How to move liquid uphill against a thermal gradient, without moving parts

I am looking for a conceptual way of dealing with the following. I am not looking for a set of blueprints. Consider a 5 meter x 10 cm vertical closed tube filled with a substance in the gas and ...
3
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1answer
277 views

The original thorium reactor?

With lunar thorium being common, and heavier than iron or nickel, does earth's core have the the occasional nuclear reaction?