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

静止している小さな流体要素を考えてみましょう。流体の加速度はゼロであり、一般的な運動方程式はそれに応じて単純化されます。
これらの条件下では、垂直成分のみが流体に作用する力を持ちます。
異なる流体レベルの圧力が異なる場合、垂直力成分を統合すると、2つのレベル間の圧力差が得られます。
2つのレベル間の距離がhの場合、圧力差はhで表すことができます。
ここで、hは圧力ヘッドと呼ばれ、下点と上点の間の領域内の流体による下点の圧力を示します。
上部の基準が水面であると仮定すると、表面の圧力はしばしば大気圧になります。
次に、流体の表面から任意の深さhの圧力を大気圧で表します。
これは、静止している流体の場合、表面の下の任意の点の圧力が、表面に作用する深さと大気圧に依存することを示しています。

静止ている流体の圧力変化

静止ている流体では、流体表面下のどの点の圧力も、容器の形状や大きさではなく、深さのみに依存します。静水圧と呼ばれるこの原理は、静止している流体では加速がなく、流体内の力が釣り合うために生じます。上部の流体の重量によって生じる垂直方向の力のみが、深さによる圧力変化に寄与します。

 流体内の 2 つの異なるレベルで圧力を測定する場合、圧力の差は、これらの点間の流体の重量によるものです。この差は、圧力水頭で表すことができます。圧力水頭は、流体の深さと流体が及ぼす圧力を関連付ける概念です。圧力水頭は、2 点間の垂直距離または深さに正比例します。流体内の点が深いほど、その上にある流体の重量による圧力が大きくなります。

 流体の表面が基準点である場合 (圧力は多くの場合大気圧)、表面下のどの深さでも、圧力は大気圧とその点より上の流体が及ぼす追加の圧力に等しくなります。この関係は、水中の圧力の理解、タンク内の水圧の決定、流体力に耐える構造の設計など、多くの実用的なアプリケーションの基礎となります。

静止している小さな流体要素を考えてみましょう。流体の加速度はゼロであり、一般的な運動方程式はそれに応じて単純化されます。
これらの条件下では、...

Education

JoVE Core

Civil Engineering

土木工学

Unit 1

ユニット1

Fluid Statics

流体静力学

KEY TERMS AND CONCEPTS

主要用語と概念

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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