# Questions tagged [fluid-statics]

Fluid statics or hydrostatics is the branch of fluid mechanics which deals with the study of fluids at rest and the pressure exerted by it on an immersed object. If your question is about the study of fluids in motion, use the tag "fluid-dynamics" instead.

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### High School Problem

Draw the FBD diagram of a sphere of density $\rho_1$ and radius $R$, initially falling with velocity $v$ in a fluid of viscosity $η$ and density be $\rho_2$. Also list the forces acting on the body. (...
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### What's the physical meaning of static pressure & dynamic pressure?

as an undergrad i had a doubt regarding the physical meaning or feel of these terms could anyone please make me understand these in connection with the Bernoulli equation .
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### When calculating the terminal velocity of droplets, why do we not account for viscosity?

When I am asked to work out the terminal velocity of an object, I set up the equation, weight = upthrust + viscous drag, insert the appropriate values, and then rearrange the equation to find v. In a ...
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### Can a fluid layer float on air? Yes. And can a toy boat float upside down on the underside of the fluid? Apparently yes [duplicate]

For those who haven't seen it, this appeared in Science News (with a link to the original Nature article). It was news to me that a (viscous) fluid could float on air, provided it was shaken. This ...
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### What what will happen to the height of the Mercury column in a barometer when it is accelerated upwards?

What will happen to the height of the Mercury column of a barometer when the barometer is accelerated upwards assuming the value of g does not change with height? I think the height will remain same ...
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### Would everyone die? [duplicate]

When you open the door of your spaceship, the oxygen disappears from the ship. So if I put a very very long tube from the Earth to space, would all the oxygen from the Earth automatically aspire into ...
63 views

### Does my work suggest that the buoyancy force isn't generally just the pressure exerted on a body? [closed]

If I got it right, the buoyancy force is a result of pressure changes exerted by the gravitational force. Archimedes’ law then generally predicts the buoyant force to be $\rho_\text{fluid} Vg$. What I ...
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### I have a container completely filled with water, I add copper coins, how much can the water level rise before it spills? [duplicate]

My question is, how can I calculate the total volume such that once reached, the surface tension and cohesion are insufficient to keep the water stuck to the glass? I mean when we add objects to the ...
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### Can helium gas lift the bottle itself?

I came up with this argument: it’s possible that in the right circumstance helium would weigh more than the empty bottle. If I were to fill empty bottle full of helium can it lift the bottle in the ...
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### How does the size of a valve opening determine liquid velocity and pressure?

Say we have a water reservoir with a valve near the bottom to allow water to be released into a separate reservoir (for example, in order to avoid flooding). The valve is initially slightly (10%) open,...
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### Calculate Flow in Horizontal Venturimeter

Calculate the flow of water through a 400 x 150 mm horizontal venturimeter , when the differential gauge connected to the inlet end of the meter and It's throat shows 250 mm of mercury. Assume ...
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### What causes pressure in a liquid?

Say there is a mass inside a liquid. What causes the force on its upside downwards and the force on its downside upwards? It seems logical that the downward force is due to the weight of the fluid ...
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### Why is pressure different at different points in the same level when the water is flowing?

In fig.a below, water is to flow out from the yellow tank. But the flow is stopped because of the mercury in the green manometer. So the water is stationary. In this situation, the pressure at both ...
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### Transition from laminar to turbulent flow

Is there a mathematically rigorous definition of turbulent or laminar flow? As far as I understand, laminar flow - means, that the velocity fields varies smoothly along the distance and time. Layers ...
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### How do bubbles rise in water?

As a concrete example, consider boiling water. As water boils, bubbles form which rise to the surface. I know that things rise because of the Archimedes principle, however as far as I understand it, ...
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### Pressure at same level in a liquid in U-tube

Why does the pressure at same level in a liquid with uniform density same in both arm of a U-tube even when there is a liquid of another density at one arm? Please give me an intuitive explanation
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### Forces applied to bucket [closed]

We have two similar buckets of equal weight submerged in water, the first up and the second down. Calculation of the weight of each bucket (Can the weight of the water inside each bucket be ...
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### References for effective viscosity experiments

Presentation I am studying the following fluid mecanics problem : let's consider a domain $\Omega$ filled with water. In this fluid, we can find perfectly spherical particles of radius $\epsilon h$ ...
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### Variation of atmospheric pressure with depth in U-tube

In my physics book "Fundamentals of Physics" by Jearl Walker there is a figure that shows a U-tube with uniform cross-sectional area. The U-tube contains two liquids in static equilibrium: ...
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### Why do we consider only liquid-air surface forces in capillary rise?

Consider this diagram from wikipedia. Now the diagram clearly depicts forces due to three interfaces. But in the derivation of capillary rise, we only consider the force due to Surface Tension of the ...
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### Surface tension in a water drop

Consider the above image This is a pretty standard diagram but it makes no sense to me. I have some questions regarding it. Why are we taking surface tension of air-solid interface into consideration ...
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### Free Body Diagram of Capillary Rise

I found have found several diagrams for capillary rise and they often display different forces. What is shown in one diagram may not be covered in the other. Can someone provide me with the free body ...
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### Line of action of buoyant force [closed]

Question: Show that the line of action of the buoyancy force on an arbitrarily shaped body submerged in a liquid passes through its center of mass My observation: I know that buoyant force is equal to ...
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Assume that density of the body is less than the fluid. If we put a body in a given fluid the buoyant force equalise the weight of the body. If we increase weight, the buoyant force increase? If it ...
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### Answers to “More Questions without Explanations” in “Thinking Physics” by L. C. Epstein

In the book Thinking Physics is Gedanken Physics by Lewis Carroll Epstein is after each part the section “More Questions without Explanations”, every question with more answers, but only one of them ...
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### Defying gravity with vertical shaking? [closed]

I saw this video on levitating a denser liquid on less dense air by vertical shaking. But I couldn't understand some points in the video. Particularly: How did the liquid levitate? I think it's ...
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### Can you explain the meaning of buoyancy, written here?

I got this Archimedes' principles from a website named smithplanets.com Can you explain why we cut the volume of water equivalent to the weight of an object when the object is floating in the water ...
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### Columns of liquid on top of gas, when and why does gas bubble up through the liquid?

I have a long straw ("small" diameter tube of constant cross-section) hanging vertically above me. The straw is filled with liquid (water). I blow a finite volume of air (gas) into the lower ...
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### Rate of change between radius and temperature in a spherical balloon with difference of pressure proportional to the radius

I have an spherical ballon filled with an ideal gas such that the difference of pressure between the interior $(P)$ and the exterior $(P_0)$ is proportional to the radius of the balloon: P-P_0 = \xi ...
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### Hydraulic jack and pascal's law

When using the hyraulic jack , I am totally convinced that the pressure at the initial phase must be the same in the interconnecting liquid and both surfaces where force is applied (pascal's law) , ...
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### Having difficulties deriving the formula for the force acting upon a dam with height $H$ and width $L$

I was recently fiddling around with the derivation of the formula for the force acting upon a dam with height $H$ and width $L$, which in my textbook is derived by integrating the term $dF=p(z)Ldz$ ...
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### Why does a floating object displace more substance than a sunk object? [duplicate]

Consider a box floating on water having a coin on top, now suppose after some time by some external influence, the coin is dropped into water. After doing the calculations, to my surprise, I found ...
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### How to derive the hydrostatic equilibrium equation from the variational principle?

I was reading the book "Advanced Stellar Astrophysics" (William K. Rose, 1998) and I came across a different approach to deriving the hydrostatic equilibrium equation. First he defined the ...
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### Will a plastic feel less heavy when I put it in a bucket of water and carry it?

If I'm carrying a bucket of water in one hand and a piece of plastic in the other, and then I decide to keep the plastic in the bucket of water (it floats). Will it feel less heavy in the second case? ...
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### Lattice Boltzmann method: properties of D2Q37 stencil and beyond

I am new in the world of Lattice Boltzmann method (LBM). I have just found in this paper  the following statement: A D2Q37 Lattice Boltzmann scheme correctly reproduces the equation of state of ...
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### Water level changes after scrap iron thrown off a barge [closed]

I'm currently trying to work through Physics by HRK, Edition 5. I've come across this problem in the Fluid Statics section which I, being an amateur, decided to google. The exercise reads: A barge ...
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### Contact Angle vs Wetting Angle

On this site, among others, the angle used in determination of the surface tension forces on a solid object suspended in a liquid is referred to as "the contact angle". ($\theta$ in this ...
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### Physically, how does erection work?

All articles I found explain a human male erection through biological mechanism. However I am still curious how such process can make the male sexual organ "stand up" during an erection. ...
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### Stress and Strain lag for viscous materials

As stated here, In purely viscous materials, strain lags stress by a 90 degree phase. How can we derive this statement? Is it experimental? If not, which is its proof and what is the physical cause ...
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### Smaller droplets == smaller surface tension?

When applying soap liquid on the inner surface of swim goggles, the surface tension of the water decreases and small droplets of water on the surface won't form, therefore the fog won't form. In this ...
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### How does gravity, viscosity, IMF help a liquid spread on a surface?

If I have a bottle full of water and I turn it upside down at a small height above a flat horizontal surface while it’s cap is open, the water spreads on the surface. If I used a metal solid in place ...
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### Pressure of 2 immiscible liquids of diffrent density in a u tube

2 diffrent liquids in a u shaped tube can have height difference at equilibrium but when I try to analyse the pressure at the same level of c,on the surface of more denser liquid there is only ...
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### If I had a non-rotating whirlpool, what equation can I use to calculate the inward changing water velocity based on the distance from the whirlpool?

I'm trying find an equation that if given a non-rotating whirlpool with some inward velocity of water at the mouth of the whirlpool. What will the velocity or acceleration of the water be at some ...
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### Change in length of the body immersed in a fluid

When part of a body is submerged in a fluid of density D1 in a container accelerating with accln 'a' . Why wouldn't the length decrease? My professor already told me that the pseudo force acting on ...
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### Fluid dynamics and Bernoulli equation

What is the basic difference between static, dynamic and hydrostatic head in bernolli equation? Is static pressure gauge pressure or thermodynamic pressure?
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### Flow rate of an open tap

If I have an open tap such that there is a continuous stream of water falling through height $h$, is the flow rate the same at every point on $h$?
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### Temperature effect of rising helium balloon in air

I wanna consider some cases and make sure if im right , if i have fixed volume balloon filled with helium , and let balloon fly in air , 1) if air temperature increases , ( without increasing temp of ...
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### Conditions for water to go down from high places

I've noticed that all of the above-ceiling water tanks are piped in a way that ensures to be open to the air at the tank, and then these water-carrying pipes go down to the kitchen or rest rooms,.....