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Fluids and Hydrostatics

Hydrostatics is the study of fluids at rest and belongs to the field of fluid mechanics, also known as hydraulics.

The principle of hydrostatics states that the pressure difference between two points in the same liquid is equal to the product of the specific weight of the liquid and the difference in levels. This principle is expressed in the following formula:

P2 - P1 = γ * (h2 - h1) (10)

P1, P2: Hydrostatic pressure of points 1 and 2.

γ: Specific weight of the fluid.

h2, h1: Pressure at points 1 and 2.

In thermodynamic physics, hydrostatic pressure is the pressure exerted by the fluid at rest on its own weight. In hydrostatics, or the study of fluids at rest, there is hydrostatic pressure and atmospheric pressure, the latter being the pressure exerted by the atmosphere on the fluid.

The solid, liquid, and gaseous states behave under the same laws, but fluids have the special ability to change shape, increasing their volume, not their mass.

Thus, hydrostatics is measured through the density (p), gravity (g), and depth (h) of the fluid, and not by its mass or volume. Hydrostatic pressure is defined by the following formula:

P = pgh

P: Pressure

p: Density of the fluid

g: Acceleration due to gravity (9.81)

h: Depth of the fluid column

To calculate hydrostatics and its pressure, two principles that define its behavior must also be taken into account:

Pascal's principle, which states that a liquid at rest exerts pressure in all directions.

Archimedes' principle describes how increasing depth causes greater pressure, allowing objects within the liquid to float.

Hydrostatic pressure is the pressure exerted by a fluid at rest due to its own weight. It is defined as the product of fluid density, acceleration of gravity, and the depth at which the fluid is located.

Activity. Answer the following questions.

Remember to review the answers to the open-ended questions at the bottom of this page.

1. What principle states that a fluid transmits pressure in all directions?

a. Pascal

b. Archimedes

c. Newton

d. Bernoulli

2. What happens to the pressure if the density of the fluid increases?

a. Decreases

b. It remains constant

c. Increases

d. Disappears

3. Which of the following factors does NOT influence hydrostatic pressure?

a. Density

b. Gravity

c. Depth

d. Volume

4. What pressure does a column of water 10 m high (density 1000 kg/m3) exert?

a. 9,810 Pa

b. 981 Pa

c. 98,100 Pa

d. 981,000 Pa

5. What is the pressure difference between two points of a fluid at rest at different depths?

a. ΔP=mg

b. ΔP=ρg

c. ΔP=Vg

d. ΔP=γ(h2​−h1​)

Once you click this button, the questions will close and you will not be able to change your answer.

6. What is the difference between hydrostatic pressure and atmospheric pressure?

7. If the density of water is 1000 kg/m3, what is the hydrostatic pressure at a depth of 5 meters?

8. How does increasing depth affect hydrostatic pressure?

9. What happens to the shape of fluids at rest in relation to hydrostatics?

10. What is the general formula for hydrostatic pressure, and what does each symbol represent?

Still have questions?

We recommend visiting the following materials for further knowledge or understanding on the topic:

1. The Hydrostatic Equation

2. Hydrostatic Pressure

3. Hydrostatic

Answers to open-ended questions:

6. Hydrostatic pressure is the pressure exerted by a fluid at rest due to its weight, while atmospheric pressure is the pressure exerted by the atmosphere on bodies or fluids.

7. P = 1000 × 9.81 × 5 = 49.050 Pa

8. The greater the depth, the greater the pressure, since the column of fluid above the point in question is greater.

9. Fluids adopt the shape of the container but maintain internal pressure based on their density, gravity, and depth.

10. P = ρgh. P is the pressure, ρ is the density of the fluid, g is the acceleration due to gravity, and h is the depth.




References:

1. De Enciclopedia Significados, E. (2024, 12 julio). Hidrostática (Física): Qué es, Concepto y Qué estudia. Enciclopedia Significados. https://www.significados.com/hidrostatica/ https://www.significados.com/hidrostatica/

2. National Oceanic and Atmospheric Administration [NOAA]. (s. f.). The Hydrostatic Equation. https://www.aoml.noaa.gov/ftp/hrd/annane/prelim_notes/hypsometric_equation.pdf https://www.aoml.noaa.gov/ftp/hrd/annane/prelim_notes/hypsometric_equation.pdf

3. Hydrostatic Pressure. (s. f.). https://jackwestin.com/resources/mcat-content/fluids/hydrostatic-pressure https://jackwestin.com/resources/mcat-content/fluids/hydrostatic-pressure

4. Simon Fraser University [SFU]. (s. f.). Hydrostatic. https://www.sfu.ca/~mbahrami/ENSC%20283/Lecture%20presentations/Fluid%20statics.pdf https://www.sfu.ca/~mbahrami/ENSC%20283/Lecture%20presentations/Fluid%20statics.pdf

5. Less Boring Lectures. (2021, 23 febrero). HYDROSTATIC PRESSURE (Fluid Pressure) in 8 Minutes! [Vídeo]. YouTube. https://www.youtube.com/watch?v=3MvRpp7WnK0 https://www.youtube.com/watch?v=3MvRpp7WnK0

6. Physio Flip. (2021, 19 enero). Hydrostatic and osmotic pressure | Introduction to #edema [Vídeo]. YouTube. https://www.youtube.com/watch?v=rPWf43lYcBU https://www.youtube.com/watch?v=rPWf43lYcBU

7. The Organic Chemistry Tutor. (2017b, noviembre 12). Introduction to Pressure & Fluids - Physics Practice Problems [Vídeo]. YouTube. https://www.youtube.com/watch?v=kkq8ruV8_Jw https://www.youtube.com/watch?v=kkq8ruV8_Jw