What is Hydrostatic: Definition and 241 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. R

    Hydrostatic force on a semicircular wall

    Homework Statement This isn't really a homework problem, it's a passage in the lecture notes that I don't quite get wholly. So here's the passage: "To compute the hydrostatic force on a semicircular wall of radius a which forms the end of a swimming pool filled with water, between D(y) = 0 and...
  2. M

    Hydrostatic Problem: Three tube Manometer

    Hi guys, new to the forum here. I have of a conceptual question that I can't wrap my head around. Here's the situation: there's a reservoir filled with water attached to a "three-column manometer" with each column open to the atmosphere. The horizontal tube that connects all three of the...
  3. A

    Understanding Hydrostatic Pressure: Comparing Green and Orange Axis

    We are interested in pressure along green axis in the first picture and along orange axis in the second picture. Air pressure is constant everywhere. For the first case: under water surface: p = patm + ro.g.h patm = 105 Pa = 105 kg.m-1.s-2 ro = 103 kg.m-3 g = 10 m.s-2 h =...
  4. H

    Calculating the Hydrostatic Force on the wall of a Cylindrical Tank

    How would I go about calculating the hydrostatic force on the walls of an upright Cylindrical Tank. To keep it simple, it is completely full of water, is 1m tall, has a diameter of 1m. Many thanks for anyone that can help.
  5. M

    Resultant Force Due to Hydrostatic Pressure

    I've got a question concerning the resultant force due to hydrostatic pressure. I understand how to calculate an object with uniform dimensions as depth (and pressure) increase. But I got thrown a serious curve ball on a Statics test. The situation was such: A downward facing isosceles...
  6. D

    Negative pressure & Hydrostatic paradox

    2 parts: 1. What does it mean if you get a negative gauge pressure value when calculating from manometer containing compound liquid? When calculating absolute pressure how does atmospheric pressure affect this negative pressure ie. atmospheric pressure opposes the direction of force? 2...
  7. T

    Calculating Hydrostatic Force of a Submerged Semicircle

    Homework Statement There is a semicircle submerged in the water. The distance between the surface and the top of the semicircle is 2 ft, and the radius is 5 ft. Find the hydrostatic force. The answer is 1.2 * 10^4 N. Homework Equations y = sqrt(25 - x2) The Attempt at a Solution...
  8. H

    Hydrostatic Force Problem - Calculus

    Homework Statement Find hydrostatic force on the vertical side of the tank that has the shape of the region bounded by the curves y=2x2, y=8. Assume that the tank is full of water. Homework Equations F=pgAd (force = density*gravity*area*depth)The Attempt at a Solution I know I need to set up...
  9. P

    Calculate Hydrostatic Force on 4x3 ft Triangle in 6 ft Tank

    A tank that is filled 6 feet deep with water has a 4x3 foot, right triangular plate submerged into it so the 3 foot side is parallel to the bottom of the tank. The top of the triangle is one foot below the surface. Calculate the hydrostatic force on one of it's sides. The density of water is...
  10. M

    Hydrostatic Force (Out of my Calc book)

    This is technically a physics problem but its straight outta my calculus book... The instructions are to express the force as an integral and evaluate it. My problem is just the initial set up. I've tried a couple of different ways and none of them get me the answer that I am seeing...
  11. A

    Hydrostatic equilibrium violated in the sun

    Hi there Problem is: if hydrostatic equilibrium were violated by .01% so that 0.01% of the gravitational force were imbalanced by the pressure gradient, estimate how long it would take the sun to change its radius by 10%. My attempts at solving problem: My feeling is that the...
  12. Z

    Calculating Hydrostatic Forces in a Steel Tank with a Viewing Glass Window

    Homework Statement A steel tank is 6m long, 2m wide and 3.5m high. A viewing glass window is mounted at one side of the tank as shown. The tank contains water to a depth of 3m. The glass window is 0.2m in radius and its top is 0.5m below the water surface. Calculate the magnitude and...
  13. T

    Spherical star in a hydrostatic equilibrium

    Hello again, I've got a question about a star in a hydrostatic equilibrium. How do I derive an equation of motion for a pertubation in the full momentum equation? I'm attaching my solution (my_solution.jpg) , but I'm not quite sure about it. The full exercise is attached as...
  14. B

    Hydrostatic Pressure: Submarine Crew Escape Force Needed

    Homework Statement In a submarine, at a specific time, her bottom part is at 30m below surface. Submarine gets a part fail. If the crew would like to get out, they would have to push the door of area 0,75 m^2. Door is at the bottom of the submarine and has weight of 300 N. If you have a...
  15. F

    Thermodynamics Hydrostatic Pressure as Function of Height Question

    How is hydrostatic pressure not a function of the shape of the container? My professor says that the pressure P2 is the same for the figures on the right and left. How does the area of the two sections not matter at all? Clearly, if a plate is inserted of negligible mass, thickness, and...
  16. Z

    Pressure in Hydrostatic Equlibrium

    Homework Statement Find the pressure as a function of r for the region r<< R where R is the radius of the object. The density goes as \rho = \rho_o {(\frac{r_o}{r})}^2. Homework Equations I know how to get to the answer my problem is dealing with the infinite density at r = 0.The Attempt at a...
  17. J

    Fluid dynamics: Hydrostatic equilibrium and density stratification

    Firstly, the whole question is below, for now I need help on parts of the question- I've included it all for clarity and just in case I have further problems. An equilibrium ring of isothermal fluid orbits a star at radius R. In the plane of the ring, mechanical equilibrium results from a...
  18. Z

    Moment about shaft from hydrostatic forces

    Homework Statement A gate with the shape as shown is mounted on a horizontal shaft. Determine the net moment about the shaft from the hydrostatic forces acting on the gate. Answer: 750kNm Homework Equations h_c: height of centroid = y_c * sin(theta) y_r: location of force or centre of...
  19. K

    Hydrostatic Force and Center of a Mass - Calc 2

    Hey guys, I have a couple of problems about hydrostatic force and center of a mass that I was hoping someone could help me out with. Center of mass Homework Statement Sketch the region bounded by the curves y=2x^3, x+y=3 and y=0. Find the coordinates of the centroid. Homework Equations Sorry I...
  20. C

    Deriving Pressure on a Fluid Surface at Rest with Constant Density

    Homework Statement Consider a stationary fluid (u=0) with constant density and take F= (0,0,-g). Find P(z) which satisfies P=P_a on z=h_0 , where z is measured positive upwards. What is the pressure on z=0? Homework Equations Euler's equation: \frac{Du}{Dt}=-\frac{1}{\rho}\nabla P...
  21. A

    Relativistic Hydrostatic Pressure in Constant Gravitational Field

    Hi everybody, When I have a perfect fluid within a constant gravitational field g, the pressure at depth z simply reads P=\rho g z, where \rho is the fluid density (incompresible). If now my g is still constant, but my fluid is relativistic. Not because it's moving (everything is still)...
  22. F

    Hydrostatic force on submerged curved surface

    Homework Statement Hi i know how to do these problems but its calculating the weight of the fluid, which you have to do to minus it from the vertical force. But in the solutions to the problem is say that the volume is R^2 - Pie *(R^2)/4 *1 The only thing i want to know is why is that...
  23. C

    Why Does Volume Not Affect Hydrostatic Pressure? | Dave

    One of the six conditions of hydrostatic pressure is said to be that the volume of the liquid does not affect the hydrostatic pressure. Can anyone explain why? Thanks Dave
  24. S

    How can hydrostatic pressure drop to zero?

    Hello everyone, If this is a vessel the hydrostatic pressure would drop along the vessel due to resistance. My question is why does hydrostatic pressure drop if hydrostatic pressure is due to gravity. Gravity is always there, even if the molecules lose hydrostatic energy, they would gain it...
  25. P

    How Does Atmospheric Pressure Affect Hydrostatic Calculations in Tank Design?

    Dear guys, I got a common doubt regarding the pressure at the bottom of a open tank filled with water. 1) Assume a tank of 2m height, filled with water. So the hydrostatic pressure at the bottom of the tank will be 0.2 bar(rho*g*h). Wondering! it is less then atmospheric pressure(1 bar)...
  26. W

    Hydrostatic force acting on beam

    Attached is the problem i am trying to get to grips with along with my current line of understanding, The column seen is a side section slice from the design of a water tank. The column is designed to take the load of the water. The column is designed with 2 unequal angle 75x50x6 steel...
  27. D

    Hydrostatic pressure, and force

    if i am asked to find the hydrostatic pressure on a certain object emerged in a liquid, am i meant to use the barometric or manometric pressure? when asked for hydrostatic force, should i find the force on the object , or the force that the solution applies to the object??
  28. R

    Hydrostatic pressure on triangular plate

    Homework Statement A triangle with base 3 m and height 4 m is submerged vertically in water so that the tip is even with the surface. Express the hydrostatic force against one side of the plate as an integral and evaluate it. Homework Equations \int_{a}^{b}{\rho}g(x)w(x)dx The Attempt at...
  29. 3

    Hydrostatic Pressure and Force

    Homework Statement An aquarium 5ft long, 2 ft wide, and 3 ft deep is full of water. Find the hydrostatic pressure and the hydrostatic force on the bottom of the tank. Homework Equations P=g*\rho*h F=m*g=g*\rho*A*h \rho=62.5 \frac{lbs}{ft^3} g=32 \frac{ft}{s^2} The Attempt...
  30. N

    Hydrostatic Test: Calculate Leakage Rate of Thread & Coupling

    I am looking to conduct a hydrostatic test on two short pieces of pipe connected via coupling a round thread coupling. Our intent is to pressurize the sample to 6000 kPa and hold for 1 hour to see if there is any sort of pressure drop, and if so what is the leakage rate of the system through the...
  31. S

    Internal energy of a hydrostatic system in a reversible adiabatic process

    Homework Statement A simple hydrostatic system is such that PV^k is constant in a reversible adiabatic process, where k > 0 is a given constant. Show that its internal energy has the form E=\frac{1}{k-1}PV+NF(\frac{PV^k}{N^k} where f is an arbitrary function. Hint: PV^k must be a function of...
  32. N

    Hydrostatic Equilibrium and Forces

    Homework Statement Two Piston cylinders are connected by a pipe with radius (Rp). Piston 1 which is located at height (h1) with an area (a1) is pushed down with a force (F1). In the opposite cylinder, Piston 2 is at a height (h2) with an area (a2), with force (F2) pushing up on the piston due...
  33. Totalderiv

    Hydrostatic Equilibrium in General Relativity

    Homework Statement Finding the TOV equation of Hydrostatic Equilibrium in General Relativity Homework Equations The Attempt at a Solution For the above questions, I've scanned in my work...so that might help instead of typing it on the computer...
  34. Totalderiv

    Hydrostatic Equilibrium in General Relativity

    What am I doing wrong?
  35. V

    How Does Hydrostatic Equilibrium Apply to a Polytropic Star?

    Homework Statement I am working on a problem in which I need to calculate the hydrostatic equilibrium for a spherically symmetric star described by a polytropic equation of state. There are two boundary conditions. Homework Equations All I know is gravity and pressure are going...
  36. S

    Automobile Hydrostatic Pressure

    Homework Statement 1) A typical automobile tire has a gauge pressure of around 30 Ib/in^2. How much is that in pascals? If a car weighs 8897N(=2000lb), how much area(SI units) on each tire is in contact with the road? 2) A swimming pool 5m wide by 10m long is filled to a depth of 3m...
  37. L

    Hydraulic Dune Buggy Design: Is My Math Correct?

    Hi all. I don't know if I have posted this in the right section, but I am hoping someone might be able to lend me a hand with a project. A friend on mine and I are always looking to build something challenging and unique. We recently finished building a truck completely from the ground up...
  38. S

    Find the hydrostatic force exerted on a sphere

    Homework Statement a spherical vessel is made by fitting together identical hemispherical halves across a horizontal plane.It is filled completely with water of weight W.What is the the resultant hydrostatic pressure force on the bottom half of the vessel? anyone please help me how to...
  39. A

    Calculate Hydrostatic Force Exerted on Plane Submerged in Water

    I need to find the hydrostatic force exerted on a plane submerged vertically in water. I attached a diagram of the problem. Here are the basic definitions: --------------------------- d=distance from surface, p=density, P=pressure p=\frac{m}{V} P=pgd=\delta d F=mg=pgAd...
  40. G

    Hydrostatic pressure in a submerged pipe

    What would be the hydrostatic pressure near the top of a vertical pipe closed at the top and open on the bottom? Would you calculate the pressure density*gravity*depth measuring depth from the top of the pipe or from its opening at the bottom or the difference between the point of measurement...
  41. Totalderiv

    Hydrostatic Equilibrium in General Relativity

    Background info: Hello PhysicsForums, I'm currently a high school student in calculus and physics. I've been teaching myself Astrophysics by using the books Stellar Structure and Evolution by Springer-Verlag and Principles of Stellar Evolution and Nucleosynthesis by Clayton. I realize these are...
  42. R

    Calculating Hydrostatic Blood Pressure in Different Body Positions

    Homework Statement a person is 1.8 m tall, standing upright. His heart is 1.4m above his feet. He is doing a head stand. Calculate the hydrostatic blood pressure in (a) his feet and (b) his head. Homework Equations P-Po= density x g x d The Attempt at a Solution When...
  43. D

    Help needed: Hydrostatic pressure forces and torque

    Homework Statement Consider the dam in example 3. Suppose there is a rectangular gate near the top of the dam that can be used to release water. The gate is 4 m wide and 3 m tall and is hinged at its top edge so that it will close under its own weight. Determine the torque on the gate for...
  44. D

    Hydrostatic pressure forces and torque

    Homework Statement Consider the dam in example 3. Suppose there is a rectangular gate near the top of the dam that can be used to release water. The gate is 4 m wide and 3 m tall and is hinged at its top edge so that it will close under its own weight. Determine the torque on the gate for...
  45. S

    Hydrostatic Pressure Explained: Why Does Water Flow & Stop?

    I don't understand. If there is a bucket of water and you put a tube inside the bucket and blow at one end and then release water flows out of the tube. Why does this happen. Also when you raise this tube water stops. Why? This is not homework or anything. :smile:
  46. A

    Hydrostatic Pressure: Calculate Force on Cylindrical Tank

    Homework Statement A cylindrical tank, with base radius 9.4 meter, lies on its side and is partially filled with a liquid whose density is \sigma=1260 kilograms per cubic meter. The liquid fills the tank to a maximum depth of 14 meters. Determine the amount of force (in Newtons) exerted on a...
  47. S

    Hydrostatic Force: Impact on Sidewall and Bottom of Box

    You have a rectangle box filled with a liquid to height H. How will the force on the sidewall of the box change if the height (H) is increased without adding anymore fluid? (i.e. a smaller solid box is added to displace the liquid). Assuming the equation F=specific weight*depth of center...
  48. B

    Solving a Hydrostatic Problem: Cylinder Height in Water and Oil

    Homework Statement A Cylinder got ratio of 15 cm, and h=15. Their mass=7kg. This is floating in water. After we put oil on it (density=725kg/m^3), on the water. Calculate what's the height of cylinder when its in oil. Answer=7.6cm Homework Equations F=D x V x g The Attempt...
  49. M

    Hydrostatic Pressure: Liquids or Air?

    Is the equation for hydrostatic pressure limited to liquids? Or can it be used for air pressure as well?
  50. P

    Hydrostatic Thrust Calculation for Trapezoidal Retaining Wall

    Homework Statement A trapezoidal mass concrete retaining wall 6m high,1.5m wide at the top and 3m at the base retains water to its full height. calculate the hydrostatic thrust on the retaining wall and a factor of safety against oveerturning. take the density of water to be 1000kg/m3 and the...
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