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# Questions tagged [fluid-statics]

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### Wood in water and buoyant force

Wood doesn't sink in water because its density is less than water density. So $ΣF=0$. But what is the force that counterbalances the gravitational force if the wood does not sink in water so that ...
76 views

### What is the physical meaning of static and velocity pressure?

According to Bernouli's equation, the static pressure inside a pipe with streamline and steady flow decreases with fluid's velocity. One explanation to rationalise this phenomenon is because velocity ...
29 views

### Gravity and objects in substances

This is probably a matter of terminology and me not finding it due to the lack of it. An apple falls from a tree on the ground due to gravity. Yet, if it falls into a water pit it floats on top of ...
231 views

### Why does Pascal's principle apply to a Hydraulic jack but not to stream lines in a stream tube?

Pascal's principle says that the pressure applied at one point in an enclosed fluid under equilibrium conditions is transmitted equally to all parts of the fluid and thus the pressure in e.g. ...
60 views

### Pressure on side walls of container [duplicate]

My textbook mentions the standard derivation of finding pressure at a depth of a liquid by considering a cylindrical portion of liquid an then using the equilibrium of forces and hence pressure comes ...
594 views

### Ice is in alcohol, if the ice melts does fluid level go up, down or stay the same?

The answer key says fluid level goes down. So, I understand the the ice would sink since density of alcohol is less than ice. However, I remember that when ice is in water and it melts, the water ...
83 views

### Champagne bubbles and gravity

One of the influences on bubble size is the speed with which a bubble rises in a glass - this, I believe, is due to the force of gravity which acts on the liquid around the CO2. The greater the ...
80 views

### Atmospheric Density

As I was reading my textbook, I noted that it stated that the atmosphere becomes less dense as height increases. I am unable to understand this. I understand that pressure decreases as height ...
26 views

### How to calculate the buoyance's work when releasing bar above water

The exercise is to calculate the buoyance's work when releasing a bar of mass $m$, lenght $L$ and cross section area $S$ just above water. My problem is that I am assuming my referencial on the water ...
88 views

### Hydrostatic force on spillway gate?

I'm designing an spillway gate that, as the water exceeds a specific height, then it opens pure mechanically, it means the hydrostatic force compensates for the weight of the gate. As you can see the ...
117 views

### Free falling fluid pressure distribution

Consider a free falling tank of fluid. The goal is to find the pressure distribution. My intuition says that there should be no pressure distribution; the pressure should be uniform since the ...
45 views

### The vertical component of surface tensions in wetting

To find the contact angle made by a droplet on a flat surface at equilibrium, we take the sum of all surface tensions at the boundary of the droplet to be equal to zero (Wikipedia link). Projecting ...
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 ...
669 views

### How to calculate speed of buoyant object rising

I'm looking for a formula to calculate the speed of object in buoyancy. Is there any formula available for this purpose? For example, if I release one liter water bottle from under 10 meter distance ...
520 views

### Physical meaning of same pressure on the same plan (hydrostatic paradox) with different weight above them [duplicate]

In this picture the points on red have the same pressure because the weight of the fluid is the same above them. But according to pascal law the point on black must have the same pressure(both 3 ...
106 views

### Confusion regarding Archimedes principle

Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body ...
560 views

### How do speed and density change in a turbulent flow?

Suppose a fluid passes from having laminar flow, to having a turbulent flow (like when passing after an object). How do fluid speed and fluid density change after that?
67 views

### Physical meaning of variation of force of pressure with altitude in fluid

We usually prove that pressure is a function altitute Z. Imagine a cube in a fluid, then the force of pressure on the bottom surface is higher than the force of pressure on the top surface. But we don'...
37 views

### What is the force being applied? (Water Pump Problem)

Lets talk about the water pump problem where you must pump water up and out of a tank and figure out how much work was needed to accomplish this. So assume we have a cubic container with length 1 on ...
158 views

### Does venturi effect violate pascal's law?

If we use Bernouill's law to compare pressure between point 1 and point 2, we find that P(2)gdH=0, we conclute P(2)=P(1). I must have made a mistake but where is?
72 views

### Is it possible to generate energy by exploiting the hydrostatic pressure gradient?

Is there any way to harness the hydrostatic pressure gradient to generate energy? The pressure at the surface of an ocean is atmospheric pressure.As we descend down the ocean, the pressure increases ....
234 views

### Why is the pressure same in a horizontal plane in a static fluid?

One of the common explainations involve a cylindrical flask filled with fluid and Newton's second law. But such explainations is specific. What could be possible explanation in a case in which the ...
258 views

### Hydrostatic pressure in a gas

I have a physical picture of hydrostatic pressure ($dp/dh = \rho g$) in liquids, interpreting it as the weight of the water column. Now in a gas, the molecules are much further apart than in a liquid....
67 views

### Balloon rising up in water and reading on the scale

The balloon rises beause of buoyant force being greater than its weight, I'm interested in the change in scale reading while the balloon is still completely underwater. And let's ignore any viscous ...
620 views

### How can pressure act in both the up and down direction?

It says in my textbook that pressure is a vector. So how does it act both in the up and down direction in the same body of water as seen in this image?
228 views

### Archimedes Principle $\Delta M$ formula

i'm trying to determine a formula for $\Delta M=M-M_{apparent}$ in terms of $\rho_o , \rho_w , M$ for a fully submerged object and I have no idea where to begin. I have attempted to draw a force ...
104 views

### How to find velocity of water flow and $Q$ if I know static pressure at the end of the pipe of known diameter?

I have a pipe. At its end I have mounted pressure meter. Of course there is no circulation. Water pressure meter is a kind of stopper for water. I know diameter of the pipe, and I know its pressure in ...
267 views

### Is Pascal's law incorrect?

Consider the figure given below. Here I'm gonna talk about capillarity. The liquid inside the beaker as well as the column is water. As water has a tendency to rise in the capillary as shown, doesn't ...
64 views

### Would a conical siphon be able to lift water greater than 10.1 m?

In a discussion with my father, he argued that a siphon can only pull water up to a limit of ~33 ft (10.1 m). I understand that this limit would apply to water with a density of 1.0 g/cm at sea level (...
70 views

My points of interests is at point A and B. I want to investigate how much pressure is acting on this two points. (Ignore Atmospheric pressure and work in gage pressure). Since the oil will flow up ...
76 views

### The link between two definitions of “potential density”

In Kundu's book , 4ed, P21, they define the potential density $\rho_\theta$ like this: However, later in P22, they define the potential density gradient as It seems to me that the potential density ...
27 views

### fluid statics doubt (regarding free body diagrams)

why does the pressure exerted by liquid on side walls increases with depth? please explain in detail.Thanks in advance
81 views

### What's measured by weighting a fluid?

Suppose you have a glass of water at room temperature. Now suppose you put the glass of water on a weighting scale. What the quantity actually measures ? I have read that in fluids are basically lots ...
936 views

### Why should pressure be same at same height?

Suppose I have an U shaped tube, and I fill the left side with mercury and right side with water. Also I take another U shaped tube, and fill it with water completely, as shown in the below picture: ...
53 views

### The other force in centrifuge

Consider a rotating centrifuge and a reference frame rotating with it. On every "piece" of fluid inside a centrifuge acts centrifugal force, but what are the other forces that make every piece stay in ...
526 views

### Torque exerted by pressure in a fluid

If I have a solid rigid body (let us call it a duck) in a static regime submitted to the forces of pressure $P$ of a fluid (no shear forces) I can easily calculate the total force $\mathbf{F}$ exerted ...
7k views

### Can ants walk on liquid mercury? [closed]

I'm not a physicist, but I was wondering: Can ants walk on dense liquid like mercury and why?