# What is Hydrostatics: Definition and 73 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. ### Just curious about many things like hydrostatics

How did you find PF?: I was Googling something and this forum popped up answering a completely different question. It was still very interesting. I wasn't sure what this forum was about and I was prompted to sign up while trying to figure that out. I then received an explanation and am glad I...
2. ### I Hydrostatics: Pascal's principle and ocean depth

Hello everyone! I've been learning about hydrostatics and one thing that I've heard is that the pressure is the same throughout confined incompressible fluids, this is one of the reasons hydraulics work, because when you have the same pressure per square meter, you can change the mechanical...
3. ### 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.
4. ### Oscillation of a boat in still water (Metacenter and Center of Mass)

Let’s say we have a boat whose longitudinal axis is the y-axis (which goes into the screen in the figure below) standing upright in a still water . ##S## is the Center of Mass of the boat and ##C## is the Center of Mass of the displaced water.On ##S## lies the force ##\mathbf W##...
5. ### Misc. Hydrostatics problem in a water vessel

I am trying to design a water vessel system that maintains it's water level as it is consumed. In item 1. It's a simple water barometer, where the height of water in the column can be supported by atmospheric pressure until 10.34. In item 2. There are two columns that are open to atmosphere...
6. ### 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...
7. ### My Second Post: Change in Magnitude of Normal Force?

Hello, Let us imagine a solid immersed in a liquid in a container such that the density of the liquid is less than the density of the solid. This means that the solid must sink. Let us study the solid when it reaches the bottom surface and is now at rest. The forces acting on the solid when it...
8. ### Hydrostatics: Immersing a metal cube in water......

Homework Statement A metal cube is placed in an empty vessel. When water is filled in the vessel so that the cube is completely immersed in the water,the force on the bottom of the vessel in contact with the cube (A) will increase (B)will decrease (C)will remain same (D) will become zero...
9. ### 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 *...
10. ### Surface Tension, find number of stitches to be made

Homework Statement The tension in the skin of the left ventricle of heart is 4.90 N/m. A cut is made on the left ventricle during surgery. How many stitches must be used to repair the cut? Each stitch will safely support a tension of 0.4 N. Homework Equations Surface tension = force/length...
11. ### I Object suspended over an empty bucket

I was recently tutoring a first year student, and a question of her assignment was as follows: Suppose that that you have a bucket of water over a scale. If you then partially submerge an iron rod in the water, while holding the rod so that it does not touches the bucket, will the reading on...
12. ### Hydrostatics, Length of a mercury column

Homework Statement What will be the length of mercury column in a barometer tube, when the atmospheric pressure is 75 cm of mercury and the tube is inclined at an angle of 60° with the horizontal direction? Homework Equations Pascal's Law The Attempt at a Solution l ⋅ sinϑ = h l = h / sinϑ l...
13. ### Hydrostatics, find length of kerosene column in U tube

Homework Statement A glass tube is bent into a U shape. Water is poured into the tube until it sands 12 cm high on each side. Kerosene (density = 870 kg/m3) is added slowly to one side until water on the other side raises 5 cm. What is the length of kerosene column? Homework Equations (ρhg)1 =...
14. ### 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...
15. ### 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...
16. ### How to Determine Centroid of Gate Hydrostatics

Homework Statement In this image : http://ezto.mheducation.com/13252703414204806874.tp4?REQUEST=SHOWmedia&media=2.83qs.jpg Why does the weight of the gate have a centroid at 2R/pi away from the force F? Homework Equations The centroid for a half circle in both x and y directions is =...
17. ### Vapor Pressure In Closed Cylinder

Hi There, I am trying to understand if I have a vacuum in the below scenario or simply just really low pressure. A pump supplies a pipe with a constant supply of water at one end (Point A) the water discharges several kilometers away at some lower elevation (Point B). At "Point A" a valve...
18. ### Pressure is equal or force is equal at the bottom?

Problem Statement: Both containers are just equal in volume and having same height; you can assume one is upside down of another. What is pressure at the bottom of the containers. Let's say left side is container 1 and one on right side is 2. Relevant equation: h is the depth of fluid from the...
19. ### 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...
20. ### Bouyant force when there is no liquid beneath an object

Homework Statement A block floating on water contained in a vessel is pushed inside until it touches the bottom of the vessel and then released. Will the block come back? Homework EquationsThe Attempt at a Solution [/B] Bouyant force acts because the pressure on the bottom of the block is...
21. ### Problem involving gas laws and hydrostatics

Homework Statement A glass tube filled with air at room temperature is 1.54m long. The tube is closed on one end, and open on the other. When submerging the open end in water, the water in the tube rises by 0.14m. How much of the tube is above the water's surface? The correct answer is 0.40m...
22. ### Thermodynamics -- hydrostatics question

Good afternoon. You are a student of the career of physical I am 'm like someone aids with the second section (II) the following problem because I do not understand much. Thank you very much. Problem: Considering that the effects of pressure variation with height are due only factor hydrostatic...
23. ### Hydrostatics on Plane surface

Homework Statement A 3 m long gate of weight 4 kN per unit width is hinged at O and sits at an angle θ as a function of water height h above the hinge. (A) Using a y-axis measured up from the hinge, derive a general relation between h and θ, with all other variables evaluated in the relation...
24. ### 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...
25. ### Hydrostatic and atmospheric pressure

So I've been wondering, 10.3 meter of water amount for one atmosphere, and according to Pascal's law pressure can compute by P=P0+ ρgh. If we have a glass with 10 cm of water inside , the pressure in the glass would be lower than atmospheric pressure and therefore when you turn the cup upside...
26. ### Hydrostatic Pressure Question?

Homework Statement During a test dive in 1939, prior to being accepted by the U.S. Navy, the submarine Squalus sank at a point where the depth of water was 73.0 m. The temperature at the surface was 27.0 ∘C and at the bottom it was 7.0 ∘C. The density of seawater is 1030 kg/m3. A diving bell...
27. ### Fluid Hydrostatics: Homework Solutions & Explanations

Homework Statement Attached below Homework EquationsThe Attempt at a Solution My first confusion is with the pressure measuring device, i just converted the units into Pa by dividing by 1.02x10-5 such that: Pressure at the top of the tank = (0.07/1.02e-5) - (9800*0.3) = 3922.75Pa So on the...

haruspex submitted a new PF Insights post Frequently Made Errors in Mechanics - Hydrostatics Continue reading the Original PF Insights Post.
29. ### Hydrostatics on plane surface (basic fluid mechanic Q)

I don't understand how they got the "position of individual forces". For F1, I'm guessing they used a pressure diagram and that's why it's 2/3 from the tip of the triangle. But why wouldn't the force act on the centroid for this square section (thus its 3.5/2)? But for position of F2 (y2)...
30. ### Hydrostatics with density and area

Homework Statement A dam is made which is rectangular and flat in profile. It is a depth of 25m and a width of 100m and holds back fresh water which has a density of 1000 kg m3 . What is the total force that the water exerts on the dam? Homework Equations F=ρA |dF|=pdA d/dz p=-ρg The Attempt...
31. ### Hydrostatics: pressure and forces and density

A 5.0 kg cube of metal has a density of 3000 kg m3 and is held by a vertical string while immersed in water which has a density of 1000 kg m3 . Assume that the cube is oriented so that all the faces are either vertical or horizontal. 1. What is the difference in pressure between the top of the...
32. ### Water hydro statics and presure

hey guys. bellow is an upside down cone frustum with the dimensions given bellow where the green R is the radius of the larger circle and the blue r is the radius of the smaller circle and the red h to be the height of the object knowing that volume of this shape is calculated as...
33. ### Help please -- Problem of hydrostatics force in flat surfaces

Homework Statement Homework EquationsThe Attempt at a Solution I could know the pressure in point B If I calculate the heigh of pressure I got: But I don't know where is my free surface in the container 3, is it down?? I don't know how to keep doing it...
34. ### Hydrostatics: What remains the same in a fluid?

I am looking into hydrostatics, but am now very confused about what has to remain constant in an incompressible fluid. I initially thought that pressure has to be the same all throughout the fluid, and that this is the reason why you can use water or oil when raising a car- you apply a small...
35. ### What is the Equation for Water Pressure on a Dam Wall?

Homework Statement Consider a simple model of a free-standing dam, depicted in the diagram. Water of density ρ fills a reservoir behind the dam to a height h. Assume the width of the dam (the dimension pointing into the page) is w. (a) Determine an equation for the pressure of the water as...
36. ### Metallic coin over wooden block in glass of water - buoyancy

Homework Statement So there is some water inside a container; the height of water inside the container is l. I placed a wooden block on the water and it's floating to some height x, on top of the block is a metallic coin (see the diagram below). What will happen if I throw that coin inside the...
37. ### Hydrostatics: long, bent tube

A uniform long tube is bent into a circle of radius R and it lies in vertical plane. Two liquids of same volume but densities ρ and δ fill half the tube. Show that the angle θ = arctan{(ρ-δ)/(ρ+δ)}
38. ### Hydrostatics - Benzene poured into uniform U shaped tube with water

Homework Statement A uniform glass tube is bent into a U shape. Water is poured into the tube till it stands 10cm in each tube. Benzene (sp gr = 0.879) is then slowly added to the tube on the left side until the water rises 4cm on the right. What length is the column of benzene when the...
39. ### Hydrostatics (abs pressure)

Homework Statement (a) Calculate the absolute pressure at the bottom of a fresh-water lake at a depth of 22.5 m. Assume the density of the water is 1.00x10^3 kg/m3 and the air above is at a pressure of 101.3 kPa. (b) What force is exerted by the water on the window of an underwater vehicle at...
40. ### Hydrostatics question - angled triangular gate?

Homework Statement The question asks to find the magnitude of the pressure force on the gate: The Attempt at a Solution Here is the part of the solution: I don't get why zc is 3.667m. Shouldn't it be 3 + (2/3)sin40 since you want the depth of the centroid from the surface to the...
41. ### Hydrostatics - Why is the pressure force the same?

Homework Statement The Attempt at a Solution So for the cone there is the weight of the liquid (W), the upward force (F_y), and the pressure force acting on the bottom (F_v): F_v = W - F_y For the cylinder there is only the weight of the liquid and the pressure force acting on the...
42. ### Basic Hydrostatics question, RL applications

Any feedback will be appreciated. I live on a semi-rural property and the owner charged me with a real-world problem involving hydrostatics. On the water pump, we currently get only 11 psi of water pressure. His goal is to get 30psi. His plan is to get a 2500 gallon water tank and let...
43. ### Hydrostatics: Is There a Force at the Top?

Should there be a force from the water at the top, or no?
44. ### Hydrostatics- rearranging formula

Homework Statement Derive an equation for the pressure difference p – B in terms of ρM, ρ, L, θ, a, A and the acceleration due to gravity g Homework Equations (LHS p')= B+(ρm)g(Lsinθ+h+Δ) = (RHS p') P+ρg(Lsinθ+H) Δ=delta = La/A a= area of tube, A= area of reservoir h= ρH/ρm...
45. ### Hydrostatics and Cylindrical Tank

Homework Statement I fill a cylindrical tank of length 50 ft and diameter 90 ft with water (to the brim). What is the force the bottom 1 ft band of water exerts on the lining? Homework Equations The Attempt at a Solution My main doubt is whether i should integrate from 0 to 1 and...
46. ### Hydrostatics and work done by a gas in a situation similar to a siphon

It isn't actually homework, it was just a problem proposed and then the answer was also given, but I don't understand it and I would like some help in trying to understand. Homework Statement In a cylindrical container the water level is at 30 cm. If you float a glass bowl in it, the water...
47. ### Finding the Height of a Heavy Oil Column in a U-Tube with Mercury and Light Oil

Homework Statement U-tube has mercury of relative density 13.6. Column of light oil is poured into one limb. It is 15 cm tall and of relative density 0.78. A column of heavy oil is poured into the other limb so that it is level with the top of the light oil column. Find the height of the heavy...
48. ### Hydrostatics: U-Tube Homework Solution

Homework Statement A u-tube of uniform cross section with vertical limbs of height 20cm has mercury of relative density 13.6 in the bottom of it. The columns of mercury in each limb are 6.9cm high. Water is poured into one limb until it just reaches the top. Find the height of the water...
49. ### Help with Hydrostatics Problem

Hi I am really stuck on this problem and would greatly appreciate some help. Homework Statement Homework Equations The Attempt at a Solution I would be able to solve this if the dam wasn't curved. I would just use integration to find the magnitude of the force f = pghA. I would express a...
50. ### Hydrostatics: solving for density.

Homework Statement A block of wood floats in water with 2/3 of its volume submerged. In oil, it does so with 9/10 of it submerged. Find the density of the block of wood and the oil in terms of water's density. The Attempt at a Solution Setting the equilibrium condition (net force = 0)...