# What is Fluid statics: Definition and 55 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 Fully submerged block in a pool of water

Let’s say we let a block of iron sink into the water and it reaches the bottom. Would the force pushing on body towards the bottom be: ##F_{downwards}=mg+F_P## where ##F_P## is the force caused by hydrostatic + atmospheric pressure. The force acting upwards should be then...
2. ### B Static pressure inside the glass of water

If we had a perfectly isolated glass of water, the total pressure inside will be equal to the sum of hydrostatic and static pressure. In this case, would the static pressure be totally dependent on the temperature of water and the volume of glass? Also, consider that the glass is completely...
3. ### B Physically speaking, what happens in Torricelli’s experiment?

I understand what happens in experiment, but my understanding of pressures isn’t the perfect. Torricelli used a one meter long glass tube with opening on one end with mercury inside it. He then dipped the tube into a bowl of mercury and mercury started to dip from tube. However it stopped after...
4. ### 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 : $$F = 1/2 \rho g h_{y} A_{y}$$
5. ### How Do SI Units Affect Calculations in Fluid Statics?

For A) I used P = hpg (h=0.0125km, p=1000kg/m^3, and g= 9.8m/s^2) this gave me 122.5N/m^2 For B) I used Ptotal = Pgauge + Patm = 1.01E5 + 122.5 = 101122.5 N/m^2
6. ### Why is solid density used in this thermodynamics problem?

Callen asks us the following question in his famous textbook: I have answered as follows: However, I get the wrong answer and, in fact, the correct answer obtains from using ##\Delta P = -\rho_s g h##; that is, using the solid density for the change in pressure. Now why on earth should this...
7. ### What does atmospheric pressure have to do with the gauge pressure?

In this video( ) it's explained what is gauge pressure. Can someone please explain to me what does atmospheric pressure acting on a tube(in video at 3:51) has to do with displacement of a tube? I understand that the atmospheric pressure acts on the tube, but in the open space that does not...
8. ### Solving Fluid Statics Problem: Accounting for Atmospheric Pressure

Hi! For this fluid statics problem, One of the answers is: However, why did they assume the pressure at the top was zero? I thought the pressure at the top would be 1 atm? So tried to take atmospheric pressure into account putting 1 atm at the top, Do you please know how to get P_0A/2 so...
9. ### I How Does Surface Tension Balance Small Objects on Water Surface?

When small object such as needle is put on the surface of water it displaces small amount of water which creates a depression under the object. Such depression increases surface area of the water because of which surface tension tends to decrease it. Explanation why surface tension balances the...
10. ### Force on side of tank filled with liquid of variable specific weight

Homework Statement: An open tank with a rectangular side 1 m wide and 4 m high is filled with a liquid of variable specific weight, γ, with γ = 50 + 2y (N/m3), where y is measured vertically downward from the free surface. Find the magnitude of the force on the side of the tank. Homework...
11. ### Pressure in Forces on Submerged Surfaces

Why does the pressure we take into account is the gage pressure and not the absolute pressure? Reading Fundamentals of Momentum Heat and Mass transfer by Welty in chapter 2 it says "the magnitude of the force on the element dA is PgdA ,where Pg is the gage pressure" my question is why the gage...
12. ### What's the difference between hydrostatic force and bouyancy?

Homework Statement Homework EquationsThe Attempt at a Solution
13. ### Fluid static problem with wooden block being pulled down

Homework Statement The figure below shows a metal object (2) hanging by a thin cord from a floating wooden block (1). The wood block has a SG of 0.3 and dimensions of 50mm x 50mm x 10mm. The metal part as a volume of 6600m^3. Find the mass of the metal part and the tension in the cord. Work in...
14. ### Pressure Calculations at Points A and B using Pascal's Paradox

Homework Statement The points of interest are at point A and B, I want to calculate the pressures at that point. I am working in gage pressure so we can ignore atmospheric pressure. Homework Equations P = pgh P = sg x specific weight of water x height The Attempt at a Solution Attempting a...
15. ### Buoyancy,volume of air inside barrel

Homework Statement We are using a device(as shown in the image) to blow air into a 200L plastic barrel. We want to know how much air (volume) that is needed to raise the anchor from the seabed. Homework EquationsThe Attempt at a Solution The anchor will start moving upwards when the sum of...
16. ### Pressure at same height in same fluid?

Homework Statement A sealed has a partition stuck down in water, creating two separate air pockets. The pressure at A is measured to 95 kPa (absolute) and the temperature is 20 C. Find the pressure at B. The Attempt at a Solution Why is the pressure at A not equal to B? Doing U-tube exercises...
17. ### Pressure on a vertical rectangular plate submerged in water

The question goes as follows..: A car driver has an accident and drives into a lake. The car sinks to the bottom. The distance from the car door to the water surface is 10m. The car door is 0.9m wide and 1.3m tall. Assume that the car door can be approximated as a vertical rectangular plate and...
18. ### 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...
19. ### Force on the bottom of the vessel containing a submerged cube

Homework Statement Conside the fig below. A tank of water (height of water column b) is kept on a electronic weighing scale . a metal cube (side a and density D) is hung from a spring balance and the spring balance is slowly lowered into the tank till the cube reaches the bottom of tank. The...
20. ### Work done in expansion of a bubble

Homework Statement as title Homework Equations force exerted by atmosphere on bubble = 2(on account of dual layer) * 2pi*r*L(surface tension) work is the integral of force *dx The Attempt at a Solution so we're looking at int ( 4pi*r*L *dr) but since not it 1 particle is traveling against...
21. H

### Fluid Statics- u-tube displacement

Homework Statement A uniform U-tube is partially filled with water (ρH20 = 1000 kg/m3). Oil, of density 750 kg/m3, is poured into the right arm until the water level in the left arm rises 30 mm. The length of the oil column is then: (Answer: 40mm) Homework Equations P = pgh Pressure = density...
22. ### Understanding Fluid Statics: Solving Gage Pressure Problems

Homework Statement All over the place here so bare with me, I'll get the hang of it eventually. -----For these types of problems.. can you start at either the top of the tank or from point a? -----Given specific Gravity, you need gamma of the unknown fluid so you multiply it by the density...
23. ### How to find the angle of a pinned rod at a certain depth

Homework Statement The uniform 5 m-long round wooden rod (ρ = 800 kg/m3 ) is tied to the bottom by a string with length 1 m. Determine the inclination angle θ if the water level is 3.5 m. What if the water level is 7m? Homework Equations Fb = ρgV The Attempt at a Solution So I'm really...
24. ### Fluid Statics: Difference Between Force Formulas

Homework Statement What is the difference between these two formulas Homework Equations 1.Force=rho*g*h*area 2. Force=rho*g*volume 3. Force=rho*height*Area Where rho= specific weight of fluid The Attempt at a Solution I am guessing that 2 is for sphere or cylinders and for 3 i think it is...
25. ### Fluid Statics: Calculate Moment on Rectangular Gate Hinged on Upper Edge

Homework Statement The rectangular gate shown in section is 3 m long (perpendicular to the paper) and is hinged about its upper edge B. The gate divides a channel leading to a fresh-water lake on the left and a salt-water tidal basin on the right. Calculate the moment, M, on the shaft of the...
26. ### What Is the Correct Ratio of Platform Sides to Lift a Car with a Boy's Weight?

Homework Statement A 1,500-kg car stands on a square platform, and a 25-kg boy stands on another square platform. These platforms are the two caps of a large oil-filled container. What must the ratio of the platform sides (large/small) for the boy to gently lift the car? -less than 1.5...
27. ### Problem in Great Courses Video On Physics

[ mod note: moved from general physics so homework template is missing ] At the end of each lesson, the lecturer gives a problem. The question is: A rectangular, flat-bottomed rowboat has a mass of 120 kg when empty. It's 3 meters long, 1 meter wide, and 0.24 meters deep. How many 85 kg people...
28. ### Pressure force in water on truncated cone with air inside

Homework Statement Consider the truncated cone tank submerged in water: inside the truncated cone tank there is air. Evaluate the forces acting on the truncated cone tank. Homework EquationsThe Attempt at a Solution The forces are the following Boyuant force : $$F_b= \rho_w g V_{tank}$$...
29. ### Floating block with objects that are thrown in a liquid

Homework Statement I'm confused about the following kind of situation. Consider a block of density ##\rho_b##, mass ##M_b## and section ##S_b## that floats on a liquid of density ##\rho_l##, in a tank of section ##\mathcal{S}##. On the block there are some objects (all equal), of density...
30. ### Why Does the Shape of a Container Not Affect Fluid Pressure Calculations?

for static fluids we have studied that p=patm +density*g*depth. and this equation is derived from Newton's laws,but in fbd why didn't we consider the force exerted by curved surface area of container,it doesn't cancel out when containers are in frustrum shape.and the vertical components add up...
31. ### Pressure exerted by a fluid in a closed container

When a hole is made in the side of the container holding water, water flows out and follows a parabolic trajectory. If the container is dropped in free fall, what will happen to the water flow? I think that the water flow will follow a similar trajectory..what effect can gravity have on it? it...
32. ### Manometer with non linear height change.

I am trying to establish a mathematical relationship between heights h1 and h2 (please refer to figure attached) for a manometer whose RHS channel is the shape of a triangle (defined by a base length and the angle theta). I want to be able to calculate the heights h1 and h2 for a given change to...
33. ### Fluid statics- pressure intensity and hydrostatic force

Homework Statement a concrete dam, 20m in height, has a vertical upstream face. if the water level is coincident with the top of the dame, calculate and plot the pressure intensity at 4m intervals over a vertical and thus determine the total hydrostatic force acting per unit width. Show that...
34. ### Fluid Statics: Find vertical and horizontal forces in tank

Homework Statement The tank shown in the figure is filled with water and fastened to the ground. There is a small opening on top of the semi-spherical part of the tank. a) What is the magnitude of the horizontal force on the screws? Explain using a free body diagram. b) Consider the proper...
35. ### Fluid Statics - net upward force

Homework Statement Find magnitude of net upward force on a cube in terms of l, ρ (rho), g and h. then show that h = m/ρl2 A solid cube, mass m, side length l, is placed in a liquid of uniform density, ρ(rho), at a depth h0 below the surface of the liquid, which is open to the air. The upper...
36. ### Fluid statics - two water tanks

Homework Statement A water tank, 3.7 m deep and 2 m in diameter, is connected at the bottom to a second water tank by using a 2 cm diameter pipe (see the figure). The tank A is open to the air and tank B is filled to the top and sealed. a) what is the mass of the water in tank A...
37. ### Archived Fluid statics and relative humidity problem

Homework Statement A tube (both ends open, height h, diameter d) is immersed into water so that length h1 of the tube is above water. Then the top of the tube is covered tightly and the tube is pulled out of the water so that length h2 is above water. The relative humidity of air is \phi and...
38. ### Very basic fluid statics and dynamics question

consider the image on the drawing at the top (above the yellow arrow) if i had some non-compressible fluid enclosed in a pipe like container that looped back in on itself (as shown in figure), and if the container was non-elastic, when i rotate this container filled with fluid such that...
39. ### Fluid Statics Problem: Calculating Resultant Force on a Dam - Solution Attempt

Homework Statement Water stands at a depth D behind the vertical upstream face of a dam. Let W be the width of the dam. Find the resultant horizontal force exerted on the dam by the water. The Attempt at a Solution So I know how to solve the problem, I was just unsure of whether we...
40. ### Maximum Capacity of a Flat-Bottomed Rowboat

Homework Statement A rectangular, flat-bottomed rowboat has a mass of 120 kg when empty. It's 3 meters long, 1 meter wide, and .24 meters deep. How many 85 kg people could it hold before swamping? Homework Equations d=m/v ? The Attempt at a Solution I need to determine the...
41. ### Fluid Statics - Forces on Submerged Surface?

QUESTION Rainwater collects behind the concrete retaining wall shown in the figure. If the water saturated soil (specific gravity 2.2) acts as a fluid, determine the force and center of pressure on a 1-m width of the wall. PROBLEM 1. What does it mean by 1-m width of the wall? Is it 1-m...
42. ### Fluid Statics (multiple choice question)

Homework Statement #1 If you hold a block of lead and an identical size block of Styrofoam under water, the buoyant force will a) be greater on the lead block. b) be greater on the Styrofoam block. c) be the same on both blocks. d) depend on the depth that each block is held. #2 Salt...
43. ### Fluid statics with Pascal's barrel

I am confused about the some of the concepts behind fluid statics. Here is an example to illustrate this, using Pascal's barrel experiment. Consider a cylindrical barrel with cross-sectional area A and height H. Now insert a straw of height h and cross-sectional area a so that the total of...
44. ### U-Tube Fluid Statics: Solving for Water Column Length and Mercury Rise

Homework Statement Mercury is poured into a U-tube. The left arm has a cross-sectional area A1=.001 m and the right has A2=.0005m. One hundred grams of water are then poured into the right arm. Determine the length of the water column in the right arm of the U-tube; given the density of...
45. ### Fluid statics seems easy but can't figure it out .

Homework Statement A cylindrical tank of internal diameter 1.5m and length 2.0m is mounted on a trailer. When the tank is filled with water the combined weight is 55 kN. Find the weight of tank plus trailer with the tank full of methyl alcohol (relative density 0.789). Homework Equations...
46. ### Fluid Statics Center Of Pressure

Hey guys I'm needing some help here its to find the center of pressure on a plane vertical. Sorry guys for the way I've set out all of this but its the only way i know how basically I'm just wondering how to calculate the experimental and theoretical center of pressure of this lab I'm...
47. ### Fluid statics specific gravity question

Homework Statement A block of wood with a specific gravity of .6 with a volume of 100 cm^3 is made to just float in H2O by hollowing out some of the wood and replacing it with a substance of specific gravity of 6.5. How many grams of wood were replaced. Homework Equations Not totally...
48. ### Question about fluid statics and dynamics

This is not a homework assignment but a general question about something I found in my textbook. It pertains to fluid statics and dynamics and it says that: We can make the flow of a fluid visible by adding a tracer. This might be a dye injected into many points across a liquid stream or...
49. ### Fluid Statics Problem: Determining pressure change in adiabatic atmosphere

Homework Statement At ground level in Colorado Springs, Colorado, the atmospheric pressure and temperature are 83.2 kPa and 25 C. Calculate the pressure on Pike’s Peak at an elevation of 2690 m above the city assuming an adiabatic atmosphere. Known Patm = 83200 Pa T0 = 25° C z-z0 = 2690 m...
50. ### Fluid Statics: Solid & Hollow Spheres in Water

Homework Statement A solid sphere and a hollow sphere of same radius and same material are dropped from the top of a beaker filled with water. The height of water in the beaker is 'H'. Which sphere will reach the bottom of the beaker earlier and why? (Neglect any viscous force)