Name: how buoyancy keeps bodies stable in water
Uploaded: 2025-02-13T15:43:11.000Z
Duration: 1 min 11 s
Channel: JoVE

Lorsqu’un corps stationnaire est entièrement ou partiellement immergé dans un fluide, le fluide exerce une force sur le corps, appelée force de flottabilité.
Cette force agit à travers un point connu sous le nom de centre de flottabilité.
La force de flottabilité est égale au poids du fluide déplacé par le corps et agit verticalement vers le haut, ce phénomène est connu sous le nom de principe d'Archimède.
Un corps est en équilibre stable s’il revient à sa position d’origine après avoir été déplacé, ce qui définit sa stabilité.
Lorsque le corps s'incline, le centre de flottabilité se déplace et l'axe du corps s'aligne avec la ligne verticale à travers le nouveau centre de flottabilité, connu sous le nom de métacentre, qui détermine la stabilité du corps.
Un corps complètement immergé reste en équilibre stable pendant de petites rotations si le centre de gravité est en dessous du centre de flottabilité.
Lorsqu’un corps flottant s’incline, la force de flottabilité se déplace pour créer un couple de rappel avec le poids, même si le centre de gravité est au-dessus du centre de flottabilité.
Cependant, les corps grands et minces peuvent connaître un couple renversé, entraînant une instabilité.

flottabilité et stabilité des corps immergés et flottants

Buoyancy and Stability for Submerged and Floating Bodies

En mécanique des fluides, la flottabilité et la stabilité sont des concepts clés pour comprendre le comportement des corps immergés et flottants. Lorsqu'un corps stationnaire est entièrement ou partiellement immergé dans un fluide, le fluide exerce une force sur le corps appelée force de flottabilité. Cette force agit verticalement vers le haut à travers un point appelé centre de flottabilité, qui est le centre du volume de fluide déplacé. Selon le principe d'Archimède, l'amplitude de la force de flottabilité est égale au poids du fluide déplacé par le corps.

La stabilité d'un corps dans un fluide dépend de sa capacité à revenir à sa position d'origine après déplacement. Pour les corps immergés, la stabilité est déterminée par les positions du centre de gravité et du centre de flottabilité. Si le centre de gravité est en dessous du centre de flottabilité, le corps reste en équilibre stable. Pour les corps flottants, la stabilité résulte de l'interaction entre la force de flottabilité et le poids du corps. Lorsque le corps s'incline, le centre de flottabilité se déplace, créant un couple de rappel qui ramène le corps à l'équilibre. Cependant, les corps grands et minces peuvent subir un couple de retournement, provoquant une instabilité et un risque de chavirage.

Flottabilité et stabilité des corps immergés et flottants

Lorsqu’un corps stationnaire est entièrement ou partiellement immergé dans un fluide, le fluide exerce une force sur le corps, appelée force de flottabilité.
Cette force agit à travers ...

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

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

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 after it is moved. For submerged bodies, stability depends on the center of gravity and the center of buoyancy. If the center of gravity is below the center of buoyancy, the body stays in stable equilibrium.

Floating bodies become stable through the balance between buoyant force and weight. If the body tilts, the center of buoyancy shifts. That shift creates a restoring couple that turns the body back toward equilibrium. Tall, slender bodies may instead develop an overturning couple, which can make them unstable and lead to capsizing.

How Buoyancy Keeps Bodies Stable in Water

how-buoyancy-keeps-bodies-stable-in-water

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 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...

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 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 buoyant force, the center of buoyancy, and Archimedes’ principle explain why submerged and floating bodies stay stable or capsize.

How Buoyancy Keeps Bodies Stable in Water | 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.

How Buoyancy Keeps Bodies Stable in Water

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