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

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3answers
167 views

Why does it seem as if big vehicles “attract” mine when I drive close to them?

When I drive a car at high speed and when I am near to another big car (like a van, or transport vehicle) I feel an attraction to or something push me toward the other big car. What's the physics in ...
1
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1answer
264 views

Derivation of Archimedes' principle

It is my understanding that upthrust from a liquid on a body is due to pressure difference on the top of the body and the bottom of the body. How, then, is this fact used in order to derive/work out ...
2
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1answer
39 views

ϕ-component of equation of moition: proving a relationship [closed]

I have the following velocity vector (in spherical polars): \begin{equation} \textbf{v} = u \hat{\textbf{r}} + v_{\phi}\hat{\boldsymbol\phi} \end{equation} Where $u(r) = u$ and $v_{\phi} (r) = ...
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1answer
71 views

How can I carry out this force summation? Control volume involved

I have a stationary jet engine on a test stand, like shown in the next figure: The control volume is indicated in the figure as a dashed rectangle, that has its left side far upstream of the ...
16
votes
7answers
846 views

Physics of how the cochlea isolates frequencies along its length?

Can anyone explain the separation of frequencies along the basilar membrane of the cochlea please? (equations would be nice) I understand it being related to the resistance caused by fluid in the ...
0
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0answers
97 views

Self-made air pump - What does it take to pump up a balloon?

We are building a simple altitude-controlled balloon (idea borrowed from Google Loons). As part of that, we need an air pump to inflate a balloon acting as ballast (which is called a Ballonet in ...
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0answers
30 views

Calculating power in fluid systems with $pQ.$

I was wondering: say we have a fan which is being used to provide lift to some mass, like in a simple air cushion device, where the air has to flow through a chamber beneath the fan. Let's say that ...
0
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1answer
56 views

How are shock waves related to sound, and are there equations describing its density, size, and pressure?

How exactly does one model a shock wave? I've done a lot of searching and have failed to find any equations where we're able to relate things such as its pressure, density, temperature etc. I've ...
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0answers
22 views

Roughness of the Surface and the time that a toy hovercraft hovers?

My question is about a toy CD hovercraft. I want to know that how does the time that the hovercraft hovers scale with roughness of the surface? Thanks in advance
0
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1answer
86 views

Water clock in ancient time [closed]

A Water clock used in ancient Greek is designed as a closed vessel with a small orifice O.The time is determined according to the level of the water in the vessel. What should the shape of the vessel ...
3
votes
1answer
115 views

What's up with my whipped cream? [closed]

I got a latte with whipped cream this morning, and towards the end of the drink I noticed a peculiar effect. Regardless of how I turned the cup and thereby the coffee, the whipped cream pieces ...
1
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1answer
81 views

The demise of the Tacoma Narrows bridge was casused by aeroelastic flutter. But isn't that just a special case of resonance?

Much of the research I've done on the Tacoma Narrows bridge disaster of 1940 attribute the collapse of the bridge due to aeroelastic flutter - not strucural resonance. But isn't aeroelastic flutter ...
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1answer
33 views

Conceptualising the switch from discrete molecules to the continuum (fluid dynamics)

I understand that $\rho(x,t)$ represents the density of the small volume surrounding the point $x$. However what have I done with the discrete molecules in the process of averaging?
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2answers
75 views

Deriving an Euler Equation

In this derivation is it necessary to write the triple integral, as I thought that if we are dealing with one fluid particle it only contains one "point" and hence we do not have to take a sum?
0
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1answer
182 views

What does the continuum hypothesis of fluid mechanics mean?

I'm a bit confused by the continuum hypothesis stating that fluid are continuous objects rather than made out of discrete objects. Say for $\rho (x,t)$ (density) is there more than one fluid ...
0
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1answer
32 views

Pressure as the magnitude of the reaction force

Here $\vec{F}$ is the reaction force caused by the interaction of the fluid particle on the surface and another. I don't think the two parts I have highlighted in green tally with one another. If ...
0
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2answers
86 views

Mass flux across a volume

Here mass flux means the mass flow rate, units: kilograms/second This is for a one-dimensional flow Firstly is the reason why the mass flux/ mass flow rate $=$ $\rho(x_1,t)A(x_1,t)u(x_1,t)$ ...
-1
votes
1answer
275 views

Continuity equation in fluid mechanics

The continuity equation in fluid mechanics states that $$ \frac{\partial\rho}{\partial t} + \nabla\cdot(ρ\mathbf u)=0 $$ Can you explain to me what is the physical meaning of each term of the ...
1
vote
1answer
109 views

Is the Mass flow rate (Mass flux) a scalar quantity?

Wikipedia states that mass flow rate is a scalar quantity, however Mass Flow Rate= Density x Cross Sectional Area x Velocity and velocity is a vector quantity, so this would imply Mass Flow Rate is ...
1
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1answer
120 views

Rate of Dripping of tube

My original problem was to discover the rate at which leaking taps dripped, and its relation with the tap's size, radius, etc. However, I have no clue how taps work, so I simplified the problem. ...
0
votes
1answer
21 views

What to measure for cylinder stiffness/compressibility?

I have 2 cylinders made from different polymers. Both cylinders are made to 'accept' the same volume of water. When I fill cylinder 1 it is subjectively stiff while cylinder 2 is subjectively floppy. ...
1
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2answers
152 views

How to calculate liquid pressure regardless of the gravity?

Assume we have a balloon in a tank filled with a liquid , without any gravitational forces: We just know the Temperature, V0 and V1 I want to calculate the pressure exerted from the liquid on the ...
2
votes
0answers
79 views

Where can I find a table for NIST standards on temperature and pressure?

The Wikipedia article Standard conditions for temperature and pressure notes that IUPAC and NIST are two of the most common standards for temperature and pressure in use. Even if I could have gotten ...
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3answers
63 views

Why is mass per second constant in the Equation of continuity?

Why should the mass per second be constant in the equation of continuity? Why can't the mass accumulate inside a tube?
5
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3answers
95 views

Walking on water

I was wondering about walking on water. I wonder if we can use surface tension to do this. Lets say I make a pair of shoes in shape which has infinite perimeter (e.g a koch snowflake) with glass. Now ...
0
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0answers
45 views

What will happen to this fan in this situation?

Lets say I have a pipe with a fan at the end of it and it is drawing ambient air from the other end of the pipe. Once I account for some blockages and looking at the fan curve, it was found the ...
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2answers
148 views

By what mechanism is lift produced on a rotating cylinder in an inviscid flow?

I am taking some introductory fluid dynamic classes, and have become very confused by the Kutta-Joukowski theorem. One of the conclusions that can be derived by applying Kutta-Joukowski is that a ...
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1answer
163 views

Why does a propeller suck in air from the front?

A rotating but fixed propeller sucks in air from the front. What is the cause for this acceleration of air particles? Since propeller blades act like rotating wings, my best guess is that the blades ...
3
votes
2answers
1k views

Is Magnus effect a corollary of Bernoulli principle?

Magnus effect is commonly explained using Bernoulli principle. However, taking the lift on a rotating cylinder as an example, the velocity difference is caused by the extra work done by the rotating ...
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0answers
44 views

Superfluids (meaning, properties)

I am curious as to what a superfluid is? I have seen videos that say that they have zero viscosity, and I know that it means that there is no friction between the layers of the fluid. But what is its ...
0
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2answers
64 views

Microscopic definition of dynamic pressure of fluids

So we have a moving fluid and we know from Bernouli's equation that there is a term called dynamic pressure(not to be confused with the hydrostatic pressure of the fluid). So,what exactly is it and ...
0
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1answer
79 views

What is the difference between high speed water supply and high pressure water supply coming out of a hose?

According to Bernoulli's principle, $P + \frac{1}{2} d v^2 + dgh = constant$ where, P is pressure, d is density of water, v is velocity and h is height. Assuming that height of a plastic pipe is ...
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1answer
42 views

Tsunami effects of a nuclear explosion

Sea surface nuclear explosion arouses a tidal wave of water. How does this kind of wave compare to naturally occurring tsunamis? E.g. what would be the potential of a 100KT bomb 100km away the from ...
0
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2answers
156 views

Why does this capillary action generator not work?

So I was doing a bit of reading. Apparently the the obstacle to generating energy from the forces driving capillary action is breaking the surface tension at the top of a capillary tube. It is just ...
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0answers
21 views

Practical nozzle question / mass of finger?

A spray bottle i own broke off its compressor tip so i fashioned another one from a rubber tube, a pen lid, an ear plug and a 1 mm radius tube from a computer cleaning duster. The opening of the ...
2
votes
1answer
139 views

Understanding equation for force acting on stones skipping over water

I think I have a decent conceptual understanding of the forces at work when stones are skipped over water. My question pertains to this equation, $$ F = C_L\rho U^2S\sin({\alpha + \beta}) $$ which ...
0
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0answers
21 views

boundary layer pipe

What is the shape of fluid(say water) on exiting a pipe due to boundary layer formation?Since the velocity decreases as we move from centerline of pipe to boundary along the radius(say fully developed ...
2
votes
1answer
62 views

Boundary Layer in aerofoil

I want to know how the top and bottom boundary layer interact at the trailing edge of an aerofoil (zero angle of attack) and what happens to the boundary layer after a small distance from the trailing ...
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0answers
44 views

What happens to the d/dr term of the continuity equation in cylindrical coordinates?

The derivation of the continuity equation in cyclindrical coordinates should look like this, $$ \dfrac{dm_{cv}}{dt}=\sum \dot{m}_{in} - \sum \dot{m}_{out} $$ where $$ m_{cv} = \rho r ...
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1answer
30 views

Liquid Flow Over Object

When there is a large object in the bottom of the ocean of height h, the surface of the ocean rises by a height less than h. In fact, if the ocean depth >> h, then the surface will rise negligibly. ...
3
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2answers
86 views

2 different density liquids in space

Lets say you are in deep space with basically zero gravity. You have a ball of water floating in front of you. If you carefully injected that ball with a syringe filled with vegetable oil, what ...
2
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2answers
124 views

Are standing waves in water exact sine waves?

In many physics demonstrations waves in water are used to illustrate principles of standing waves and wave propagation. After such demonstrations, classes tend to move on to basic problems ...
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0answers
48 views

Complex potentials in plane polar coordinates - stream function

Determine the stream function and the potential in plane polar coordinates and sketching streamlines. We need to take the value of m=1. I know how to find the stream function and velocity potential, ...
2
votes
2answers
279 views

Water Waves in the Wake of a Boat

As a boy I noticed that the waves from the wake of my model boat would fan out. If I looked at the end furthest from the boat the front had turned so that it was almost running in the same direction ...
1
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0answers
52 views

Air flow through a hole [closed]

If I drill a hole of 1 cm diameter in each of two opposite window frames of my house, assume that the temperature outside is 0 deg C, the atmospheric pressure is 1020 millibar, wind speed is 10 meter ...
0
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2answers
65 views

The relation between the velocity and the static head

I would like to ask about the Bernoulli's principle: as the principle states, increasing the velocity causes a decrease in the pressure. I made an experiment using a duct and 6 manometers and what I ...
4
votes
3answers
127 views

Is viscosity simply “slowing down time”?

The Pitch drop experiment has pitch, a fluid with extremely high viscosity, flowing through a funnel. In 85 years, only 9 drops have fallen. Photographs of the drops, however, show an appearance just ...
0
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2answers
52 views

If I accelerate a mass quickly enough through a short distance (i.e. unit step function), would I create wind, sound, and heat?

As far as I know, the movement of air molecules can result in what we call wind, sound, or heat (and maybe some other things I'm not thinking of), depending on the assumptions about its motion. Wind ...
0
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2answers
37 views

Hydro-electric gravity problem - Is there a air-resistance-like force affecting water flow down a mountain making placing hydro-electric ?

Say I have a theoretical mountain with a river starting exactly at the peak. Gravity would act on the water, accelerating it down the mountain. There would also be a force limiting the water's ...
3
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2answers
83 views

How do you calculate/estimate hypersonic leading edge and skin temperatures?

At lower speeds (below Mach 5-ish), stagnation temperature (TAT) is a very accurate proxy for skin temperature. But at mid/high hypersonic speeds (especially in the thin upper atmosphere where mass ...