# Questions tagged [fluid-statics]

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### From what point is the hydrostatic pressure formula not valid anymore?

The hydrostatic pressure formula (P=p.g.h) is used (eg) to calculate the pressure at the bottom of a container. Now this pressure is equal independent of the mass in it as long as the bottum surface ...
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### Is it possible to find the exact value of the dynamic viscosity of a fluid by applying Stokes' law?

I am a high school student who is investigating the dynamic viscosity of a fluid. Typically, high school physics model the dropping of a spherical object vertically into a viscous fluid with the ...
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### Obtain an expression for pressure difference [closed]

The question is "For the two-liquid manometer, shown below, obtain an expression for $p_1 – p_2$. Let $\mathcal A$ be the area of each tank and $\mathcal S$ the area of the tube. Let $S_3$ be the ...
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### The definition of control volume regarding fluids

I haven't seen a clear and general definition of control volume. So if you know one, skip the context below and please give me your definition and sincerely, thank you. Context: The union of all the ...
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### How can you calculate the total time taken for water to completely flow out of a container given the amount of water initially in the container?

I'm doing an experiment on changing the amount of water in the container and seeing how the time is taken changes with it. The container has a little hole at the bottom where the water flows out from. ...
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### Would I have to add any additional weight at the end of the lever of well pump (B) for it to lift the same amount of water as did well pump (A)?

The question is if I would have to add any additional weight at the end of the lever of well pump (B) for it to lift the same amount of water as did well pump (A)? My assumption is yes because of ...
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### Buoyant force on partially submerged object

Is the force exerted by the liquid, in which the object is floating, same as the buoyant force exerted by the liquid? I am confused since the object is assumed to float with some part of it above the ...
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### Why is there an upthrust?

Why is there $P_2$? Is it because by Newton's third law of motion, $P_2$ is there due to the pressure of water column of $0.7 ~m$ above the bottom.
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### Difference between static and stagnation [closed]

Consider this equation. According to my understanding, the term static and stagnation means velocity is zero. So shouldn't static temperature be equal to the stagnation temperature? What am I missing ...
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### Surface Tension of Floating Object

I was reading this thesis about surface tension and its role in floating bodies. I couldn't quite understand at page 10 how the author applied the 2D divergence theorem outside the region bounded by ...
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### Basics of static and dynamic pressure

What actually is static and dynamic pressure? Can they be felt individually? Apart from definitions and equations is there any other way to explain these two quantities?
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### Water level in connected tanks

I've got two water tanks on my rooftop(both tanks are of exactly same dimensions and are at exact same level) connected at the bottom. I fill them via an external pipe connected with a pump on the ...
6k views

When I forget to water my plants, and their soil becomes very dry, during the next watering I can see that the soil becomes hydrophobic. I can even see pockets of air between the repelled blob of ...
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### Resistance between steel wires in water delayed response

I am trying to make a wire wave gauge by measuring the resistance between two stainless steel wires. Theoretically, the output voltage reading should change the deeper the wires are in the water. If ...
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### Radius of rain drop on ground

Just an observation I made this monsoon, When a raindrop falls on the ground its colour starts to fade, this may be due to the absorption of water by the ground. But gradually the radius of the water ...
1k views

### Pressure in giant ball of water floating in space

In this question: Swimming in a ball of water in space They seem to have reached the conclusion that the pressure inside a giant ball of water in space is zero. Quoting the second answer: As a ...
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### How much motion in fluids is random motion?

Say that the only pressure differences in the atmosphere was due to the gravitational pull of the earth. That is, say pressure only changed as a function of height. So we're assuming there's no wind, ...
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### Would a giant solid column float?

This question was originally inspired by this one: Why does the air pressure at the surface of the earth exactly equal the weight of the entire air column above it In it, the author mentions a ...
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### Will mass flow rate be the same in these tank-pipe-ideal fluid systems?

The equation of continuity for pipes $$\frac{\Delta m_{1}}{\Delta t} =\frac{\Delta m_{2}}{\Delta t}$$ states that mass flow rate inside a pipe doesn't depend on pipe diameter. I'm confused on ...
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### How is it possible for tall trees to pull water to heights more than 10m?

Which force actually drives water so high up, since pure atmospheric pressure will only get you up to about 10 meters if you're using suction and a long straw and yet tallest trees are over 100 meters ...
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### Pressure variation in liquids with varying densities [closed]

There is a question mentioned in my textbook which is given below Equal masses of three liquids are kept in 3 identical cylindrical vessels A, Band C . The densities are Da,Db and Dc with Da < ...
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### Pressure at the bottom of the fluid (fluid mechanics) [closed]

There is a question given my book which is stated below The three vessels shown in figure have the the same base area. Equal volumes of a liquid are poured in the three vessels the force on the ...
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### Fluid pressure in Neumann's triangle for triple junctions

Consider a point of contact where three fluid phases meet. The Neumann's triangle rule for this case is usually written as, \begin{equation} \frac{\sigma_{\alpha\beta}}{\sin \gamma} = \frac{\sigma_{\...
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### How to measure flow rate using Toricelli's law?

For my experiment, I want to investigate the relation between height and velocity using Torricelli's law. I would like to know how I would measure the flow rate from volume in a spouting cylinder.
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### How to calculate force exerted by vacuum from size and rpm of propeller used to create it?

If a propeller of particular size pushes some volume of air out per unit time. How can the suction force be determined? How big of a particle can it suck?
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### What is buoyancy?

I’ve seen answers which cite newton’s third law as the cause for buoyant force, but wouldn’t this mean the moment an object of any weight is placed on a fluid, the fluid would immediately exert an ...
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### Can density replace buoyancy?

Recently I discussed the possibility of a flat earth, with a flat earther whom rejected much of established science, especially newton and his laws because Newton's idea of gravity rendered a flat ...
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### Why is horizontal pressure the same as vertical pressure in a static fluid?

In a static fluid, I know that because it is not moving, the pressure from the top equals the pressure from the bottom. Also, using the same logic, the pressure from the sides must be the same. Why ...
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### Does the pressure from a water tank increases as the altitude increases?

If a solenoid valve is placed right after water tank's water tap does the water pressure changes if the water tank is lifted to 3 meters? The context is this: the electric valve is functional only if ...
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### Does the mass of a beaker filled with water change due to a mass partially submerged in it?

I believe it should be different as there is upthrust acting on the second block and hence by Newton Third's Law it should act back on the liquid adding to more weight. The answer is given isn't so as ...
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### Young's equation

Can somebody derive the Young's equation for the contact angle and surface energy of a droplet. $$\gamma_{la}Cos\theta+\gamma_{ls}+\gamma_{sa}$$ I've scratched my head for days finding how it exist....
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### In fluids, what is the difference between the two forces in the formula $F=pA$ and $F=\rho Vg$?

I was doing a question on fluids which is: A living room has floor dimensions of $3.5 m$ and $4.2 m$ and a height of $2.4 m$. What does the air in the room weigh when the air pressure is $1.0 atm$?...
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### Pressure and upthrust force

What is upthrust force? Is is the pressure difference or just pressure x Area at the bottom of the surface? How does upthrust force change with depth in liquid?
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### Temperature relation to Archimedes principle

I have a probably very simple problem which I cant solve. I am weighing animals in seawater by placing them on a small PVC arm that is fixed on a balance and reaches into a beaker of seawater. On the ...
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### Barometer-an air pressure measuring device

I have read about torricelli's invention of barometer,in that he used a test tube which he filled it fully with water and also he take a container and filled that container with some water.Now he ...
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### Does a rubber pipe bears more weight when the pressure of water inside it is high?

I have passed a rubber pipe across a road to my home temporarily. The pressure of water inside the pipe is very high, the vehicles and school buses passes over it! i am interested to know that "In ...
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### Why does a helium balloon rise? [duplicate]

This may be silly question, but why does a helium ballon rise? I know it rises because helium is less dense than air. But what about the material of the ballon. It is made up of rubber/latex which is ...
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### Acceleration acquired by a metallic ball in a fluid [closed]

A metallic ball of density $4.9gcm^{-3}$ is thrown in a bucket full of water.What is the acceleration acquired by the ball?(ignore all factors except gravity and resistance given by water,ball and ...
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### What makes that bottle so bouncy?

Lets take a small coke bottle(plastic one). Now fill the bottle entirely with water not even letting a small air bubble, however a tiny bubble always form. Now this water bottle when dropped will ...
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### Transfer of gas particles during pressure change

There is a room with a known volume. The temperature and pressure are known too (STP). It is given that the window is open and there will be a pressure drop outside due to wind. I need to find the ...
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### Mercury Barometer

Why Mercury surface is flat instead of convex at 760mm Hg level in Mercury Barometer? refer the image attached. note that At top it is a vacuum and surface tension = (pi-po)r/2.
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### What makes an ideal liquid incompressible?

Just thinking about liquids and Pascal's law when, this question came. Ideal liquids, I understand, are deemed to be incompressible, which simplifies our problems while decently holding good for some ...
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### Fast reversible switching from hydrophobic(>120 degrees) to hydrophilic (<60 degrees)?

I found few papers on reversible switching from hydrophobic to hydrophilic Reversible Hydrophobic to Hydrophilic Transition in Graphene via Water Splitting Induced by UV Irradiation Light-induced ...
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### Confusion about the coefficient of surface tension and the relation between force and length of a body

I haven't found a software that can create 3d or 2d shapes filled with liquids so I posted this picture. I know that the p=2σ/r where p is the pressure that goes inside the liquid and I guess that σ ...
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### Density of different liquids in manometer

According to diagram, liquid X and liquid Y have the same pressure on mercury, but how can I know which of them will be denser, liquid X is denser than liquid Y or reverse argument?
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### Is this working by communicating vessels?

https://www.youtube.com/watch?v=JzuamK0AyC4 I think the first 2 bottles are working by communicating vessels because i think that the third bottle is with atmospheric pressure and since the second ...
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### Diameter to prevent water flow into a closed-end tube?

Imagine I drill three holes of different diameter into a large block of plastic but the holes don't go all the way through. (They form three close-ended tubes, see the image.) I then submerge the ...
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### Does a non-buoyant (denser than water) object (such as a lead diving weight) weigh any less when submerged in water?

I've just been discussing this question with my eldest son, who is an extremely intelligent man, as well as being an engineer, a sailor and a scuba-diver, and he believes that an object heavier than ...
Consider a block with density $\sigma$ kept in liquid of density $\rho$, where $\rho > \sigma$. Now what is the cause of force by which it moves upwards? Is it buoyant force? If yes, then how? As ...