Questions tagged [fluid-statics]

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47
votes
3answers
11k views

Why doesn't this perpetual motion machine using the buoyant force work?

I realize this isn't possible, but I can't see why not, especially if you change the model a little bit so that the balls simply travel through a tube of water on the way up, rather than exactly this ...
107
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8answers
43k views

Why does a helium filled balloon move forward in a car when the car is accelerating?

I noticed that when I had a helium filled, latex balloon inside of my car, it moved forward in the cabin as I accelerated forward. The faster I accelerated forward, the faster the balloon went from ...
26
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4answers
7k views

Why does a cork float to the side of a glass?

What is this physical phenomenon and when it's happen ? Please take a look at this picture: Notice: This is a cork ball attracted to sides of a glass of water
24
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4answers
13k views

The Density of Clouds

Clouds are made up of tiny water or ice droplets, depending on temperature. This implies that cloud density is greater than that of dry air. Why don't clouds sink through their surrounding atmosphere ...
6
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5answers
3k views

How does buoyancy work?

I realised, reading another Phys.SE question about balloons moving forwards in an accelerating car that I don't really understand how buoyancy works. Particularly concerning, for a SCUBA diver. The ...
5
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2answers
4k views

Does the weight of fluid in a conical container act entirely on the base?

Scenario description Lets assume both containers have a capacity of 300 litres. One is a vertical tube as shown in pic 1 Other one is more or less a V shaped containers as shown in pic 2 Both are ...
11
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3answers
21k views

Hydrostatic pressure - doesn't density vary with depth?

Our class is learning about hydrostatic water pressure and we have been told that we can calculate the force of the liquid on an object at any depth using "the density x 9.8 x the depth". However, as ...
2
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2answers
2k views

Proof of Archimedes Principle

Say I have an arbitrary body $\Omega$ and surface $\partial \Omega$ submerged in a hydrostatic fluid of density $\rho$ under the influence of gravity. How does one show Archimedes Principle? i.e. $$\...
12
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4answers
2k views

A water pipe from sea level to beyond the atmosphere

If a pipe extended from just above the ocean floor to outside the atmosphere, would water be sucked up it by the vacuum beyond the atmosphere? If a hole was made in the pipe, above sea level, how ...
3
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2answers
904 views

Pressure and weight? (hydrostatic paradox)

Consider two different shaped containers having same area: one is cylinder, the other is like an inverted pyramid (roughly). Both have the same level of water, the weight of the inverted pyramidal ...
17
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5answers
43k views

How far can water rise above the edge of a glass?

When you fill a glass with water, water forms a concave meniscus with constant contact angle $\theta$ (typically $\theta=20^\circ$ for tap water): Once you reach the top of the glass, the water-air ...
42
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4answers
20k views

Does the sea level increase if an iceberg melts?

It was claimed that if an iceberg melts in the ocean, the sea level won't change as the ice displaces as much water as there will be melted water. The other claim was that the sea level should rise ...
9
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2answers
5k views

How is the water meniscus at the edge of a capillary tube?

Suppose we have a capillary tube in which water can rise to a height of x cm. If we dip the tube such that the height above the surface is less than x, then how will the water meniscus be at the edge ...
0
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3answers
910 views

Pressure at base of 3 different dam designs

The question asks, For which design will the water pressure at the base of the dam wall be the greatest? The answer is all are equal. This doesn't make sense to me. Using the formula: P (pressure) =...
14
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5answers
14k views

If force is a vector, then why is pressure a scalar? [duplicate]

By definition pressure is the perpendicular force applied to a unit area. So it has a direction which is perpendicular to the area. So it should be a vector. But I did sone googling and found out that ...
11
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8answers
2k views

Can a ship float in a (big) bathtub?

I am confused. Some sources say it is possible at least theoretically ( http://www.wiskit.com/marilyn/battleship.jpeg ) and some say it is not true ( http://blog.knowinghumans.net/2012/09/a-...
4
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1answer
454 views

No buoyancy inside liquid [closed]

The answer to this question is given as (a) 5m. Due to the difference in pressure at the curved parts there will be a net upward force of buoyancy. And how can that be calculated without knowing the ...
2
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1answer
2k views

Why is the center of buoyancy located at the center of mass of the displaced fluid volume?

Consider Archimedes' principle Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. I do not understand why the ...
1
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1answer
132 views

Noncoalescing and bouncing droplets

if you set a dish filled with water onto a loudspeaker or other vibrator and make vibration, When it oscillates, it is possible to hold small droplets on its surface for a long time. I mean, when you ...
0
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3answers
3k views

Oscillations in U-tube [duplicate]

U-tube, of uniform cross section $S$ and opened at both ends, is filled with a liquid column of length $L$ and density $\rho$. In equilibrium the water levels in both arms are at same height. What ...
1
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1answer
974 views

Would a pipe from the surface to the Earth's exosphere suck all atmosphere to the space? [closed]

If I built a tube from Earth's surface to the exosphere, would all the air be sucked out to space? If this pipe reached to a big planet, like Jupiter, would its gravity through the pipe suck our ...
1
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3answers
819 views

Pressure and altitude

I am going to ask a simple question, for sure. The pressure with respect to the altitude is given by this formula Where sea level standard atmospheric pressure p0 = 101325 Pa sea level standard ...
1
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4answers
116 views

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 ...
53
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4answers
7k views

Why does a cup with 100 g water float when placed on another cup with 50 g of water?

Imagine we have cup A with 50 g of water and cup B (smaller in width than A) with 100 g of water. Now put cup B into cup A. If the width of both cups are of comparable size then the cup with ...
11
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3answers
862 views

Fluid Pressure: The Collision Model - Approximation or Truth?

Microscopically, the pressure exerted by a fluid on a surface in contact with it is caused by collisions of molecules of fluid with the surface. As a result of a collision, the component of a molecule'...
10
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1answer
19k views

Question on the hydrostatic paradox

The hydrostatic paradox, states that the height of the water in any container is independent of the shape of the container. This does make sense since it is only the height of the fluid ...
7
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4answers
1k views

Why doesn't hydrostatic pressure glue objects to the seafloor?

Consider a cement block of the same density as sea-water resting on the (perfectly polished) seafloor. I also assume the side-faces of the cement block are highly polished, so that no vertical ...
10
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3answers
5k views

What is the meniscus shape?

What is the shape of a meniscus? I suppose that the problem is very complex, but is the solution known at least for a liquid that wets the wall in a big vessel? (exponential, maybe?)
7
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3answers
53k views

Can pockets of air exist underwater?

If yes, why don't they fill up with water, and can you breathe the air there? Like, it's not exactly atmosphere there, but an underwater cave with higher ceiling. P.S. Possible that it has a ...
9
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2answers
1k views

At the molecular level, how is the pressure at the bottom of a lake higher than at the top?

Surely the temperature of the molecules is the same throughout the water. Using $p = \rho g h$ seems to assume a constant density as well. But then how is it that the force per unit area on an object ...
4
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4answers
3k views

Shape of a rotating fluid surface

I was going through fluid dynamics and I came upon this section on the shape of a liquid surface in a rotating cylindrical vessel. The working in the book is something like this: It considers a mass ...
2
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3answers
242 views

Is there any direction of pressure i.e. according to force applied or something..?

I was reading about pressure in general and came to know that it is a scalar and being scalar it has no direction(by definition of scalars). But I think that there is some direction as when we push a ...
1
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2answers
2k views

Negative pressure

How is negative pressure created in a fluid system?Isn't it counter intuitive that we are reducing the pressure of a system containing no molecules(zero pressure) to a lower value?
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2answers
2k views

Is Atmospheric Pressure due to weight of air or the collisions of the Molecules

This question is in response to @brightmagnus answer whose link is Pressure in Fluids,in particular horizontal pressure The question is that is the atmospheric pressure due to the weight of air or ...
1
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1answer
388 views

Does the shape of a containter affect the apparent mass of liquid inside it when measured by a scale? [duplicate]

For both containers it is true that: $p_{bottom}=p_{atm}+\rho gh$ and $F_{bottom}=a*p_{bottom} \iff F_{bottom}=a*p_{atm} + a\rho gh$ I do not know how a scale functions, but I guess that the only ...
1
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3answers
419 views

Volume of melted polar ice caps

If (or rather when) the polar ice caps melt, will they occupy more, the same or less volume? Somehow all options seem possible to me. I don't assume they are just big ice cubes floating on the poles....
-1
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1answer
3k views

Energy Conservation in Kinetic Power Plants [duplicate]

Quite recently the company Rosch has developed a new kind of power plant that supposedly utilizes the buoyancy effect to generate electricity. The apparatus consists of a vertical conveyor belt with ...
20
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4answers
1k views

Which weighs more in atmosphere, $1\,{\rm kg}$ of steel or $1\,{\rm kg}$ of feathers?

I'm having a discussion at the moment regarding the mass of $1\,{\rm kg}$ of feathers and $1\,{\rm kg}$ of steel. The person I'm arguing with states that $1\,{\rm kg}$ of feathers will be lighter ...
5
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4answers
3k views

Where is the right place to put the pressure gauge to measure the pressure of a tank?

Studying the basic concepts of Fluid Mechanics, applied to pressure gauges, and looking at schematics in many places, a question came into my mind: Where is the right place to put the pressure gauge ...
4
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4answers
2k views

Atmospheric Pressure inside a closed room

Even though they’re too tiny to see, all the molecules of air in the atmosphere above your head weigh something. And the combined weight of these molecules causes a pressure pressing down on your body ...
4
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5answers
730 views

Why does not ice float in this case just instantly after melting?

I encountered this question: A cube of ice of edge 4 cm is placed in an empty cylinder of glass of inner diameter 6 cm. Assume that ice melts uniformly from each side so that it always retains its ...
4
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1answer
345 views

Is this formula for the energy of a configuration of 3 fluids physically reasonable?

I have studied for a couple of months now a mathematical model of the energy of a configuration of immiscible fluids situated in a fixed container such that the fluids fill the container. In other ...
3
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3answers
1k views

Why is a hot air balloon “stiff”?

1) Why is a hot air balloon stiff? 2) Is the pressure inside the balloon higher than the pressure outside (atmospheric pressure)? 3) If the pressure inside is higher than the outside, how is it ...
1
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2answers
356 views

Could a really tall tube suck garbage in to space?

When I was around 10 years old, I had this idea that was supposed to solve our waste problems; I imagined having tubes miles high that would stretch in to space. Every tube would have a door at the ...
1
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1answer
1k views

Surface tension: the paper clip experiment

In the paper clip experiment, the surface tension of water prevents the clip from falling, thus we can assume it exerts a force of $mg$ (weight of clip) upwards. However, if you try to pull the clip ...
0
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2answers
314 views

Archimedes' principle

Archimedes principle says that if a body is immersed in water the weight of displaced water is equal to the buoyancy force experienced by the body. Why volume of displaced water is equal to buoyancy ...
0
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1answer
255 views

Buoyant force when object is between two liquids

Suppose we have a ball floating in liquid A. Then we pour a liquid B on top of the ball (Assuming that the liquid is poured such that the ball doesn't oscillate) . The ball rises up. Why? According ...
0
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1answer
659 views

Problem regarding Buoyancy forces and Archimedes principle

A thin-walled container of mass $m$ floats vertically at the separation surface of the two liquids of density $ρ_1$ and $ρ_2$ . The whole mass of the container is concentrated in the part of height $...
0
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1answer
11k views

How to calculate the buoyant force on a balloon at different altitudes [duplicate]

For a project into balloon simulation I'd like to know how the force on a balloon changes with altitude: I know that the Buoyant force on a balloon is: $F = (\rho_{air} - \rho_{helium})gV$ Using ...
0
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2answers
69 views

If I immerse a coin in a cup of water, help me define the forces acting on it

So the coin is hanging in an equilibrium position midway in the water filled cup, concerning the force acting on the upper face of the coin, I define it as F=mg where m is the weight of the water ...