# What is Hydrostatic pressure: Definition and 98 Discussions

Fluid statics or hydrostatics is the branch of fluid mechanics that studies "fluids at hydrostatic equilibrium and the pressure in a fluid or exerted by a fluid on an immersed body".It encompasses the study of the conditions under which fluids are at rest in stable equilibrium as opposed to fluid dynamics, the study of fluids in motion. Hydrostatics is a subcategory of fluid statics, which is the study of all fluids, both compressible or incompressible, at rest.
Hydrostatics is fundamental to hydraulics, the engineering of equipment for storing, transporting and using fluids. It is also relevant to geophysics and astrophysics (for example, in understanding plate tectonics and the anomalies of the Earth's gravitational field), to meteorology, to medicine (in the context of blood pressure), and many other fields.
Hydrostatics offers physical explanations for many phenomena of everyday life, such as why atmospheric pressure changes with altitude, why wood and oil float on water, and why the surface of still water is always level.

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1. ### B What actually is static pressure?

I’ve been confused about the term static pressure for quite some time. Different sources use very different definitions. From the problems perspective, it’s usually some external pressure. For example we are having a pool with tiny hole on the bottom which makes water level decrease and it flows...
2. ### Calculate the average force on the side walls of a container

Hi All, in the following problem: the book solution I don't understand why he added the term $$\rho g h_{z} A_{y}$$ shouldn't it just be : $$F = 1/2 \rho g h_{y} A_{y}$$
3. ### Filmmaker and inventor fascinated by Physics

Hi, my question is about electricity, hydrostatic pressure, potential energy and friction. Using an electrically powered compressor (such as compressors used to fill diving bottles) if I fill a tank of volume 10 cubic meters to a pressure of 100psi, 1. what is the potential energy stored in that...
4. ### Decompressing through an underwater horn shaped tunnel

Since the Titan sub disaster I have been thinking about the issue of protecting people from the dangers of the pressure changes associated with deep sea exploration. Reading about the Byford dolphin tragedy in particular was chilling. This was just a thought experiment of mine and I was...
5. ### I A specific case of an exception to Archimedes' Principle?

First post on this forum, hopefully in the correct category and conforming to forum rules. Will the object in below scenario move upwards, downwards or will it remain stationary? An object is submersed in a container 'A' which contains a fluid 'B' (e.g. water) The trapezium shaped object...
6. ### Hydrostatic pressure in a narrow container

I understand that pressure increases with depth regardless of the shape of the container. However, this doesn't sit well with me. Imagine a container: 8' tall x 1" wide x 1' long. The pressure at the bottom of the container is 8' x 62.4 pcf = 499.2psf. However, the weight of the water in the...
7. ### B Hydrostatic pressure in a bottle of water on ISS

Hello, I am new in physics but I really like it so far. I have a question about hydrostatic pressure. I know that hydrostatic pressure equals (height)x(density)x(g). Am I right if I say that hydrostatic pressure in a bottle of water on ISS (state of weightlessness) will be zero ? Thank you for...
8. ### Hydrostatic pressure at a point inside a water tank that is accelerating

I draw this diagram: The formula for hydrostatic pressure is: ##P=\rho g h## so I just plug everything $$P=1000 \times 9.8 \times 0.1=980 Pa$$ Will the acceleration of the cart affect the hydrostatic pressure? Another thing that came to my mind was there would be extra force coming from...
9. ### Stress in rectangular vessel subjected to hydrostatic pressure

Hi, it's not easy to find formulas for stress in rectangular pressure vessels. However, I've found some in a Polish book titled "Podstawy konstrukcji aparatury chemicznej" (Fundamentals of the design of chemical process equipment) by J. Pikon. The problem is that the book provides equations for...
10. ### Engineering Hydrostatic Pressure of Ball Floating in Liquid

Let's say there's an object floating in liquid. The depth of the object below the surface is 𝑑 and its height above the water is ℎ. The density of the ball is 𝑝𝑏 and the density of the liquid is 𝑝𝐿. The pressure above the water is 𝑃𝑎𝑡𝑚. I understand this situation when only the density of the...

12. ### Can someone please clarify this formula? (hydrostatic pressure)

Is in the bottom of a liquid the pressure equal to p 0 + ρ.g.h or only ρ.g.h? please can someone tell me this correctly?
13. ### Hydrostatics: should I use P1A1 = P2A2 or P1 = P2?

I used P1A1 = P2A2 and my professor said that P1=P2 is correct, but some sources on the internet say that P1A1=P2A2 is correct, just like I did, but unfortunately no one explains why one or the other is the correct answer. For P1A1 = P2A2 you get ρI / ρII = 1/4 and for P1=P2 you get ρI / ρII = 1/2.
14. ### Forces at the bottom of a rotating U-tube filled with water

So when the rotation starts some water will move upwards and in the vertical part of tube. I know hat centripetal force will be given by F=mv²/r Now I though of taking r as centre of mass of the water system but I don't know what to take the value of m as? Should I only consider the water...
15. ### Hydrostatic pressure of liquid in a cart on an inclined ramp

Sorry for my English, I'm Spanish. I am not able to make the force diagram for the liquid. I am still in high school and started now little hydrostatic. If someone can give me a light, I would be very .grateful.
16. ### Engineering Hydrostatic Pressure Sluice Gate - Civil Engineering

Please can you help with a question I am struggling with. I have done as much working out as I could until I was completely stumped: Calculate the concrete volume that is required to keep the sluice gate AB closed, assuming that the only resisting force is the friction between the concrete...
17. ### Compressed air pressure vs hydrostatic pressure

Hi all, I'm new on here and will start off with what I think is a simple clarification. I'm questioning my workings due to previous work being completed by another engineer and thought this was the best place to ask. Essentially we have compressed air being supplied through a hose, the hose...
18. ### Hydrostatics Pressure - Finding thrust and resultants

Homework Statement I'm getting stuck with this one and in need of some direction! Obviously I'm not looking for a direct solution, but maybe a outline of what I should be doing? (I'll attach an image in a few minutes) <Image here incoming!> Known data: d2 = d1 / 2 F = thrust force (N) Pa = ρ...
19. ### Impossible hydrostatic scenario

Homework Statement There is an infnite high hydrostatic head in an infite high tank on the surface of earth. How big is the pressure p(r) in tank at a distance r. Ignore the rotation of the Earth and assume the water stays liquid. ( So basically ignore it's an impossible scenario )...
20. ### Force to lift a pyramid that is sitting in a water tank

Homework Statement A pyramid weighing 4000 lb has a base 6ft square and an altitude of 4ft. The base covers an opening in the floor of a tank in which there is water 4 ft deep. Underneath the floor of the tank and on the water surface there is air at atmospheric pressure. What vertical force is...
21. ### Why can't we use the hydrostatic pressure gradient to do work?

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 .After a point, the pressure will be very high.Why can't we use this pressure difference to do work?
22. ### Which equation to use for hydrostatic pressure?

Homework Statement h = 10 ft RHO = 10 ppg (or pounds/gallon) Homework Equations P = 0.052 * RHO * h P = RHO * G * h I am very confused right now as why each equation gives a different answer! What are the correct units for the 2nd equation and how do I convert from second equation to the...
23. ### Water tower: Why is all the water at the top?

Hi. Most water towers store their water in a huge container at their top. Why? Wouldn't it be easier to place the container at the bottom and just add a long, thin pipe upwards to create the hydrostatic pressure? Is the problem that the container would need to endure too much pressure? Or that...
24. ### Hydrostatic pressure distribution despite fluid motion

Hello, in some exam questions I've looked at it is stated that the pressure distribution is hydrostatic, even though there is fluid motion. (In these cases the velocity has been constant over the section where the pressure is said to be hydrostatic). Is it really possible to assume that the...
25. ### Minimum gas pressure to measure its volume with an eudiometer

Hello, As you can see in the attached hand drawing+calculation, my question concerns the typical method of evolved gas volume measurement by water displacement in an inverted graduated cylinder or "eudiometer". Once a bubble (cavity to be precise) of gas leaves the end of the tube through...
26. ### Calculating pressure within a system at a specific location?

Homework Statement Solution: Homework Equations dp/dz = -ρh Pressure varies linearly with the depth. The Attempt at a Solution Firstly, I have calculated the pressure at point B. PB = PA - (0.3m)*(1000kg/m^3)*(9.81m/s^2) PB = 88057 Pa Calculating the pressure at point C. However, my...
27. ### MHB Integral Applications - Hydrostatic Pressure + Force

Question #1 - A lobster tank in a restaurant is 1 m long by 0.75 m wide by 60 cm deep. Taking the density of water to be 1000 kg/m$^3$, find the water forces (a) on each of the larger sides of the tank; (b) on each of the smaller sides of the tank.
28. ### Hydrostatic Pressure and its Effects: A Visual Explanation

Homework Statement I drew a picture[/B] Homework Equations I drew a picture The Attempt at a Solution I drew a picture
29. ### Determine Force on 6ft Door Due to Water & Air Pressure

Homework Statement Determine the total force and its direction (left or right) due to water and air pressure in the surface shown in Fig. P3.62 (lb f). The door is hinged at the top and is 6 feet wide. See attached image.Homework Equations Fp (force of pressure) = specific weight of fluid *...
30. ### Hydrostatic pressure in a tilted tube

Homework Statement Prove that the hydrostatic pressure difference between the liquid surface and the base of rightmost tube is ρgh (h is the vertical distance of the liquid surface from the base ) ? Homework EquationsThe Attempt at a Solution I would like to prove this result just out of...
31. ### Hydrostatic Pressure: Resultant Thrust & Overturning Moment

Homework Statement [/B] Hello, am i on the right track with this problem. I am not sure if i have done the it correct. The part i am unsure on is b). Not sure if i have calculated it correct. Part of a sea defence consists of a section of a concrete wall 4 metres high, and 6 metres wide. (See...
32. ### Pressure Required for Fireman to Send Water 12m High | Physics Problem

<Moderator's note: Moved from a technical forum and thus no template.> My daughter, who attends the italian equivalent of US K9, asked me some advice about a physics hydrostatic problem. > Which pressure (in atmospheres) a fireman must use to send water at 12 > meters height. I tried to use...
33. ### Regarding the pressure at a point in a "rested" fluid

Hey! I just came across this text ; from http://www.feynmanlectures.caltech.edu/II_40.html I tried to find "the law of hydrostatics" on the internet, to find no other mention of it. (would appreciate links to more details on it or any ideas regarding the topic) What is really puzzling is how...
34. ### Hydrostatic pressure (infinitesimally small column of water)

This is a hypothetical question: since hydrostatic pressure is calculated as depth of water times its density, would a column of water less than a square foot in cross section still have a pressure at the bottom of depth*density of water? For example, if I had a 1" thick by 1ft wide by 5' tall...
35. R

### Calculating Water Volume in a Tank Using Pressure Measurements

Homework Statement on a flat desk is an aquarium with a volume of 640 cm3 ,t's not full of water. The pressure to the bottom of the aquarium is 3 times bigger than to one side of it, how much water is in the tank? Homework Equations is the pressure, is the normal force, is the area of...
36. ### Calculating Filling Time for a Diving Tank with Changing Hydrostatic Pressure

Hey, Let's imagine I have a tank, filled with air at atmospheric pressure. This tank have a closing/opening valve. I dive this tank at 100m under water and opened ce valve, my filling speed will be sqrt( 2*g*h) with h=100m. Now, if i want to dive the tank (with a volume X) continuously at a...
37. ### Question about hydrostatic pressure

Hi, I have a 12(W)x18(L)x1m concrete tank installed underground and it will be subjected to pressure of 0.5bar. To test the tank for leaks, instead of pressurizing the tank using pumps or air blower, my supplier suggests we use a 1 inch hose with 1 end connected to the top of the tank...
38. ### Trying to build a gas collecting chamber above a packed bed

Hi guys, I'm a graduate student and currently doing some research on a packed bed - I want to collect gas data from the headspace of my samples so i thought of building a gas collecting chamber on top of the vessel, where i can take gas measurements using calorimetric gas tubes. I'm not sure...
39. ### Static pressure and hydrostatic pressure

Hello can someone explain the difference between static and hydrostatic pressure in terms of a water in a glass
40. ### Why does external pressure on a liquid increase vapor pressure

I was reading an online chemistry textbook that said "when a liquid is subjected to hydrostatic pressure (for example, by an inert, non-dissolving gas that occupies the vapor space above the liquid surface), the vapor pressure of the liquid is slightly raised." (link...
41. ### I Hydrostatic Pressure and Fermi Surface

How exactly does hydrostatic pressure affect the shape and size of each Fermi surface in Figure 4B? How do you read this figure or what exactly is it showing?
42. ### Calculating the hydrostatic pressure on a tube

Hey guys. I'm working on a submarine project and my goal is submerging it to 100m, but I'm having trouble calculating the parameters i need. I'm working with a perspex tube (E is about 1.3Gpa), 26mm inside diameter and 30mm outside diameter. the tube X meters long with inside pressure of 1 atm...
43. ### Hydrostatic Pressure on a Curved Surface

Homework Statement Gate AB is a quarter-circle 10 ft wide and hinged at B. Find the force F just sufficient to keep the gate from opening. The gate is uniform and weighs 3000 lbf. Figure and solution attached. Homework EquationsThe Attempt at a Solution I've been able to figure out how to...
44. ### Deriving hydrostatic pressure equation for an ideal gas

Assume: Hydrostatic Situation, ideal gas Use empirical formula T = T0 - Bz I have rechecked my work several times and can't seem to find a mistake. The answer is supposed to be: p2 = p1((T0 - Bz)/T0)(g/Bz) dp/dz = -ρg Now substitute ideal gas equation for ρ dp = -(p/RT)g dz ∫(1/p) dp...
45. ### Pressure & Hydrostatic Pressure

Hello, I would like somebody to help me with few simple questions for my homework. I did try to solve them but I failed at few of them. Here are the two papers I need to help with. I need help with the highlighted excerises. I tried some basic formulas for pressure and hyrdostatic pressure but...
46. ### Cylindrical barrel Hydrostatic Pressure

Homework Statement A circular cylindrical barrel is half full with oil. If the diameter of the base is 8.0 m, find the net force against each end if ρo = 800 kg/m3. The cylinder is on its side. Homework Equations F=P*A P=ρgdy The Attempt at a Solution P = ρo*g*h, where h is the radius which...
47. M

### Hydrostatic Pressure Curved Surface

Hi PF! I have been reading and reading for a clean explanation for the hydrostatic force of a curved submerged 2-D (or 3-D if you're up to it) surface. I really don't care what the curve looks like: quadratic, circular, partway sinusoidal, etc. All articles I read involve the centroid, but...
48. ### Fluid Dynamics - Hydrostatic Pressure #2

Homework Statement a Flat rectangular door in a mine is submerged from one side in water. The door dimensions are 2m high, 1m wide and the water level is 1.5m higher than the top of the door. The door has two hinges on the vertical edge, 160mm from each corner and a sliding bolt on the other...
49. ### Fluid Dynamics - Hydrostatic Pressure

Homework Statement A rectangular vertical plate is submerged in water. The top edge is horizontal and at a depth of 0.6m. The length of the vertical edge is 1.2m. determine at what dept under the water surface a horizontal line can be drawn on the plate such that the hydrostatic forces on...
50. ### Hydrostatic pressure - barrel vs. small cylinder of water

This problem was translated from Swedish, sorry for any grammatical errors present. The problem The grey is liquid is water. The small container is a pipe made of glas and the big container is a barrel. Water is poured into the glas pipe. When water reaches 12m over the barrel top(lid) the...