Name: hydrostatic pressure and fluid depth
Uploaded: 2025-02-13T15:43:11.000Z
Duration: 1 min 11 s
Channel: JoVE

Considérons un petit élément fluide au repos. L’accélération du fluide est nulle et l’équation générale du mouvement se simplifie en conséquence.
Dans ces conditions, seule la composante verticale a une force agissant sur le fluide.
Si les pressions à différents niveaux de fluide varient, l’intégration des composantes de force verticale donne la différence de pression entre les deux niveaux.
Si la distance entre deux niveaux est h, la différence de pression peut être exprimée en fonction de h.
Ici, h est appelé la tête de pression, qui indique la pression au point inférieur due au fluide dans la région entre le point inférieur et le point supérieur.
Si l’on suppose que la référence supérieure est la surface de l’eau, la pression à la surface est souvent la pression atmosphérique.
Ensuite, la pression à n’importe quelle profondeur h sous la surface du fluide est exprimée en termes de pression atmosphérique.
Cela indique que pour un fluide au repos, la pression en tout point sous la surface dépend de la profondeur et de la pression atmosphérique agissant à la surface.

variation de pression dans un fluide au repos

Dans un fluide au repos, la pression à tout point sous la surface du fluide dépend uniquement de la profondeur, et non de la forme ou de la taille du récipient. Ce principe, appelé pression hydrostatique, est dû au fait que, dans les fluides stationnaires, il n’y a pas d’accélération, ce qui signifie que les forces à l’intérieur du fluide s’équilibrent. Seules les forces verticales, causées par le poids du fluide au-dessus, contribuent aux variations de pression avec la profondeur.

Lors de la mesure de la pression à deux niveaux différents dans le fluide, la différence de pression est due au poids du fluide entre ces points. Cette différence peut être exprimée en termes de hauteur de pression, un concept qui relie la profondeur du fluide à la pression qu’il exerce. La hauteur de pression est directement proportionnelle à la distance verticale ou à la profondeur entre deux points. Plus le point dans le fluide est profond, plus la pression due au poids du fluide au-dessus est élevée.

Si la surface du fluide est le point de référence, où la pression est souvent atmosphérique, alors la pression à n’importe quelle profondeur sous la surface est égale à la pression atmosphérique plus la pression supplémentaire exercée par le fluide au-dessus de ce point. Cette relation sous-tend de nombreuses applications pratiques, telles que la compréhension des pressions sous-marines, la détermination de la pression de l’eau dans les réservoirs et la conception de structures pour résister aux forces des fluides.

Variation de pression dans un fluide au repos

Considérons un petit élément fluide au repos. L’accélération du fluide est nulle et l’équation générale du mouvement se simplifie en conséquence.
Dans ces conditions, ...

Education

Enseignement

JoVE Core

Civil Engineering

Génie civil

Unit 1

Unité 1

Fluid Statics

Statique des fluides

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

Pressure Variation in a Fluid at Rest

hydrostatic pressure and fluid depth

Hydrostatic pressure describes how pressure changes with depth in a fluid at rest. In a stationary fluid, the fluid acceleration is zero, so the forces inside the fluid balance. That means pressure at a point below the surface depends on depth, not on the container’s shape or size.

Only vertical forces affect the pressure change in this situation. These forces come from the weight of the fluid above a point. When pressure is compared at two different levels, the difference in pressure equals the weight of the fluid between those points.

This pressure difference is often described using pressure head. Pressure head is the vertical distance, or depth, between two points in the fluid. It shows that pressure is directly proportional to depth. The deeper the point, the greater the pressure from the fluid above it.

If the fluid surface is used as the reference point, the pressure there is often atmospheric pressure. The pressure at any depth below that surface equals atmospheric pressure plus the extra pressure from the fluid above. This relationship helps explain underwater pressure, water pressure in tanks, and the forces that fluid can place on structures.

Hydrostatic Pressure and Fluid Depth

concept of pressure at a point

Fluid Pressure at One Point

Fluid pressure at one point is the focus of this lesson. It shows that pressure in a fluid is the same in every direction at a single location. This happens because fluid molecules move randomly and collide with nearby molecules in a balanced way. At a given point, the pressure depends on the surrounding fluid molecules. It is affected by depth and density, not by the shape of the container or the way the fluid is oriented. In a fluid at rest, the pressure acts equally in all directions...

basic equation for pressure field

Pressure Balance in a Fluid Element

The pressure field equation describes how forces stay balanced inside a small fluid element. In fluid mechanics, this balance helps explain how pressure changes from one place to another within a fluid. Two main force types act on a fluid segment: surface forces and body forces. Surface forces come from pressure differences across nearby points in the fluid, so they depend on the local pressure gradient, which is the rate of pressure change with position. Body forces are spread through the...

pressure variation in a fluid at rest

Hydrostatic pressure describes how pressure changes with depth in a fluid at rest. In a stationary fluid, the fluid acceleration is zero, so the forces inside the fluid balance. That means pressure at a point below the surface depends on depth, not on the container’s shape or size. Only vertical forces affect the pressure change in this situation. These forces come from the weight of the fluid above a point. When pressure is compared at two different levels, the difference in pressure equals...

measurement of fluid pressure

Manometers and Gauges for Fluid Pressure

Fluid pressure is measured with manometers and related gauges. These tools use a liquid column to show pressure differences. The height of the column gives a simple reading of the force the fluid exerts. A basic manometer is the piezometer. It is a vertical tube that is open at the top and filled with the same fluid being measured. When the tube connects to a container, the fluid height in the tube matches the pressure inside that container. For more detailed measurements, the U-tube...

hydrostatic pressure force on a plane surface

hydrostatic-pressure-force-on-a-plane-surface

Hydrostatic Pressure on Submerged Surfaces

Hydrostatic pressure creates force on submerged plane surfaces. The force depends on the fluid pressure and the area of the surface. The way that force acts changes with the surface position. For a horizontal surface, the depth stays the same across the whole area. That means the pressure is uniform. The resultant force equals the pressure at that depth multiplied by the surface area, and it acts through the centroid of the surface. For a vertical surface, pressure increases as depth...

hydrostatic pressure force on a curved surface

hydrostatic-pressure-force-on-a-curved-surface

Finding the Force on Curved Fluid Surfaces

Hydrostatic pressure on curved surfaces is an important idea in fluid mechanics. It helps explain how water pushes on curved structures in civil engineering. Examples include reservoirs, dams, and storage tanks. The pressure changes in both size and direction along the curve. To find the total hydrostatic force on a curved surface, engineers isolate the fluid volume next to that surface. They then study the forces on imaginary horizontal and vertical planes that cut through the volume. The...

buoyancy and stability for submerged and floating bodies

buoyancy-and-stability-for-submerged-and-floating-bodies

How Buoyancy Keeps Bodies Stable in Water

Buoyancy and stability explain how submerged and floating bodies behave in a fluid. When a body is fully or partly under water and stays still, the fluid pushes upward on it. That upward push is called the buoyant force. The buoyant force acts through the center of buoyancy. This is the center of the displaced fluid volume. Archimedes’ principle says the buoyant force equals the weight of the fluid displaced by the body. Stability describes whether a body can return to its original position...

design example: application of archimedes' principle

design-example-application-of-archimedes-principle

Floating Block Buoyancy and Center of Buoyancy

Archimedes' principle is used to analyze the buoyant force on a wooden block that floats in seawater. The block has a rectangular section, and its dimensions, specific gravity, and the specific weight of seawater are used in the calculation. This setup shows how floating bodies stay in equilibrium. The first step is to find the weight of the block from its volume and specific gravity. Then Archimedes' principle is applied. The weight of the displaced water must equal the weight of the block.

key terms and concepts

Learn how hydrostatic pressure changes with depth in a fluid at rest, why container shape does not matter, and how pressure head links depth to pressure.

Hydrostatic Pressure and Fluid Depth | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

Hydrostatic Pressure and Fluid Depth

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