Name: capillary action in thin tubes
Uploaded: 2023-05-16T08:18:41.000Z
Duration: 1 min 18 s
Channel: JoVE

L’action capillaire est la capacité d’un liquide à s’écouler contre la gravité dans des espaces étroits.
Cela se produit en raison de la combinaison de deux forces opposées : les forces de cohésion, qui amènent le liquide à minimiser la surface et à former une forme ronde, et les forces d’adhérence, qui font que le liquide s’accroche à la surface.
Considérons les tubes capillaires dans deux béchers différents. Si la force d’adhérence est plus forte, le liquide forme un ménisque concave. Si ce dernier est plus fort, le ménisque est convexe.
Cette équation donne la relation entre la hauteur de montée du liquide et divers paramètres.
L'élévation de la hauteur est indépendante de la forme du capillaire mais est inversement proportionnelle au rayon capillaire et à la densité du liquide.
La montée ou la descente d’un tube capillaire dépend également de l’angle de contact. Le liquide monte si l’angle de contact est inférieur à 90 degrés et descend s’il est supérieur à 90 degrés.
L’action capillaire est essentielle au transport de l’eau et des nutriments dans les plantes et s’applique à de nombreux processus industriels, tels que la teinture et la chromatographie.

<ol>
	<li>H.C. Verma Vol 1. (2012). Concepts de physique, Section 14.14 pp.289-290</li>
</ol>

montée du liquide dans un tube capillaire

Lorsque de très fins tubes cylindriques, appelés capillaires, sont plongés dans un liquide, le liquide monte ou descend dans le tube par rapport au liquide environnant. Ce phénomène est appelé action capillaire. L'action capillaire se produit en raison de la combinaison de deux forces opposées : les forces cohésives du liquide, qui le font adhérer à lui-même et former une forme arrondie, et les forces adhésives entre le liquide et les parois du récipient, qui attirent le liquide vers les parois du récipient.

Un exemple d'action capillaire peut être observé dans l'eau qui monte dans un tube en verre étroit. Les forces cohésives des molécules d'eau font que l'eau forme une forme arrondie en haut du tube plutôt que de s'écouler sur les côtés.

Un autre exemple peut être observé dans les plantes, où l'action capillaire est responsable du transport de l'eau et des nutriments des racines vers les différentes parties de la plante. Les tubes étroits dans la tige de la plante, appelés xylème, s'appuient sur l'action capillaire pour déplacer l'eau vers le haut contre la force de gravité.

L'action capillaire joue également un rôle dans de nombreux processus industriels, tels que la fabrication du papier, la teinture et la chromatographie.

Montée du liquide dans un tube capillaire

Lorsque des tubes cylindriques très minces, appelés capillaires, sont plongés dans un liquide, le liquide monte ou descend dans le tube par rapport au liquide environnant. ...

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Education

Enseignement

JoVE Core

Physics

Physique

Unit 1

Unité 1

Fluid Mechanics

Mécanique des fluides

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

Rise of Liquid in a Capillary Tube

capillary action in thin tubes

Capillary action explains why liquid can rise or fall in a very thin tube compared with the liquid around it. A capillary is a narrow cylindrical tube, and the effect becomes noticeable when it is dipped into a liquid. The movement happens because two forces act in opposite directions.

Cohesive forces make liquid molecules stick to each other, so the liquid tends to hold together and form a rounded shape. Adhesive forces pull the liquid toward the walls of the container. In a narrow glass tube, water can rise because these forces work together in a small space.

The curved shape at the top of the water shows that the liquid is not flowing evenly down the sides of the tube. Capillary action also helps plants move water and nutrients from the roots to other parts of the plant. The xylem, which are the narrow tubes in a plant stem, use this effect to move water upward against gravity.

This process is important outside biology as well. It is used in industrial work such as papermaking, dyeing, and chromatography. These examples show that capillary action matters in both everyday liquids and specialized technologies.

Capillary Action in Thin Tubes

characteristics of fluids

Fluid Behavior Under Force

Fluid behavior under force differs from the behavior of solids. When a force acts parallel to the top surface of a solid, the solid resists it because of internal friction between its layers. This is called shearing resistance. If the force is removed, the shearing forces help the solid return to its original shape. Other deformation forces can also change the shape of a solid for a short time, as long as the force stays below a threshold magnitude. Solids usually keep their shape, which makes...

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density

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pressure of fluids

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Fluid pressure appears in many everyday situations, including blood pressure and weather systems. The same force can have a very different effect depending on the area it acts on. A force spread over 1 mm² creates 100 times more pressure than the same force spread over 1 cm². That is why a sharp needle can pierce skin with a small force, while the same force from a finger usually does not. Pressure is especially important when studying fluids. A fluid does not offer much resistance to a force...

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Atmospheric Pressure and Altitude

Atmospheric pressure and altitude are closely linked. As height increases, atmospheric pressure decreases. This happens because the gravitational force per unit area becomes smaller as we move away from Earth’s surface. To describe this change, the atmosphere is treated with a constant air temperature at a given altitude. The ideal gas law of thermodynamics is also used as a good approximation for the air. Let p(y) be the atmospheric pressure at height y. The density ρ at y, the temperature T...

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pascal's law

Pascal’s Principle in Static Fluids

Pascal’s principle explains how pressure changes move through a fluid that is not flowing. A fluid at rest is in static equilibrium. If the fluid is water, it is in hydrostatic equilibrium. In this state, the net force on any part of the fluid must be zero, or the fluid will begin to flow. Blaise Pascal described this idea in 1653 in Treatise on the Equilibrium of Liquids. He showed that when pressure changes in an enclosed fluid, that change is transmitted without loss through the fluid and...

application of pascal's law

Hydraulic Force Transfer with Pascal's Law

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archimedes' principle

Buoyant Force from Fluid Pressure

Archimedes' principle explains buoyant force in a fluid. An upward buoyant force acts on an object that is partially or fully immersed in a fluid. This force is equal to the weight of the fluid displaced by the object. To see why an object floats, imagine removing a submerged object from the fluid. The space it occupied would be filled by fluid with weight w_fl. That weight is supported by the surrounding fluid, so the buoyant force must match the weight of the displaced fluid. The principle...

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accelerating fluids

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Fluid pressure changes when a liquid accelerates inside a moving container. A beaker placed in an elevator that moves upward with constant acceleration is one example. In this setup, the pressure and buoyant force equations must be modified. To find the pressure difference, the liquid is modeled as a thin vertical cylinder with height h and an infinitesimal cross-sectional area, ΔS. Three vertical forces act on this small fluid element. The liquid below the bottom surface pushes upward, the...

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surface tension and surface energy

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excess pressure inside a drop and a bubble

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Surface Tension in Drops and Bubbles

Surface tension sets the pressure difference in small drops and bubbles. For a tiny liquid drop, gravity can be neglected, so the drop is treated as spherical. It can also be viewed as two equal hemispherical drops joined together by surface tension. The forces on the drop come from three sources. The liquid inside pushes outward, the air outside pushes inward, and surface tension acts along the diameter between the two hemispheres. Since surface tension is force per unit length, it creates a...

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buoyancy

Buoyant Force in Sinking and Floating

Buoyant force explains why objects float, sink, or stay suspended in a fluid. A fluid can be a liquid or a gas, and every object placed in it experiences this upward force. A metal ball sinks, while a rubber ball floats. A submarine also changes its buoyancy to move up or down. The force comes from pressure changes in the fluid. Fluid pressure increases with depth because the weight of the fluid above also increases. That means the bottom of an object feels more pressure than the top. This...

contact angle

Wetting and Surface Curvature

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rise of liquid in a capillary tube

Capillary action explains why liquid can rise or fall in a very thin tube compared with the liquid around it. A capillary is a narrow cylindrical tube, and the effect becomes noticeable when it is dipped into a liquid. The movement happens because two forces act in opposite directions. Cohesive forces make liquid molecules stick to each other, so the liquid tends to hold together and form a rounded shape. Adhesive forces pull the liquid toward the walls of the container. In a narrow glass...

laminar and turbulent flow

Fluid Motion Patterns in Air and Water

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Fluid Flow in Narrowing Pipes

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bernoulli's equation

Fluid Pressure and Speed in Motion

Bernoulli's equation connects fluid pressure with fluid speed. It helps explain why moving fluids can create pressure changes in everyday situations. One example is when two trains pass each other quickly and seem to pull inward. The same effect can happen when two cars pass each other at high speed. As the air between the trains or cars speeds up, its pressure drops. The air on the outside stays at atmospheric pressure. That pressure difference creates a net inward force on the vehicles.

bernoulli's principle

Fluid Pressure and Speed Changes

Bernoulli's equation links fluid pressure and fluid speed in a static, incompressible fluid. For horizontal flow, where gravitational energy density stays constant, the equation is especially useful. In that setting, the result is known as Bernoulli's principle. Bernoulli's principle says that fluid pressure drops when speed increases, and pressure rises when speed decreases. This pressure-speed relationship helps explain how moving fluids behave in simple flow situations. It also provides a...

bernoulli's principle: applications

Bernoulli's Principle in Fluid Devices

Bernoulli's principle helps explain how many fluid devices work when the fluid moves at a constant height. It is useful for devices that use fast flow to create low pressure and for devices that measure fluid speed. Some devices use this pressure change to pull one fluid into another. These are called entrainment devices. A Bunsen burner uses an adjustable gas nozzle to entrain air for proper combustion. An atomizer uses a squeeze bulb to make a jet of air that pulls perfume drops into the...

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energy conservation and bernoulli's equation

energy-conservation-and-bernoulli-s-equation

Bernoulli’s Equation in Streamlined Flow

Bernoulli’s equation describes energy in a moving fluid. It comes from the conservation of energy principle, or the work-energy theorem, applied to an incompressible, inviscid fluid in laminar, steady, irrotational flow. The equation says that pressure energy, potential energy, and kinetic energy per unit volume stay constant along a streamline. Each term has the units of energy per unit volume. The kinetic energy per unit volume is called kinetic energy density, and the potential energy per...

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viscosity

Viscosity and How Fluids Flow

Viscosity describes how easily a fluid flows. Water moves quickly, while honey and maple syrup flow slowly and stick to a surface. That difference comes from fluid friction between liquid layers and between a fluid and the material around it. In this example, water has a lower viscosity than honey and maple syrup. Viscosity is measured in newton-second per meter squared (N·s/m2) or pascal-second (Pa·s). It also changes with temperature and can differ from one fluid to another by several orders...

poiseuille's law and reynolds number

Fluid Resistance, Viscosity, and Flow Regime

Fluid resistance, viscosity, and flow regime shape how liquid moves through a horizontal tube. Fluid flows from high pressure to low pressure. The flow rate, Q, is the ratio of the pressure difference to the resistance in the tube. A larger pressure difference gives a higher flow rate. Poiseuille's law describes laminar flow of an incompressible fluid in a tube. In this relation, the factors that affect flow rate except pressure are grouped into resistance. Resistance depends on the tube size...

stokes' law

Terminal Velocity in a Viscous Fluid

Viscous forces act like friction in a liquid. They resist the relative motion of molecules and pull back on a solid body moving through the fluid. The size of this force depends on the body’s shape and size, its speed, and the liquid’s viscosity, density, and temperature. For a spherical solid object, the force in a fluid is described by Stokes’ law. This law applies only at low Reynolds number, when the flow is laminar and not turbulent. Experiments show that the force is proportional to the...

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key terms and concepts

Learn how capillary action makes liquid rise or fall in narrow tubes, why cohesion and adhesion matter, and how plants use xylem to move water.

Capillary Action in Thin Tubes | JoVE K12

physics

JoVE Core Physique présente plusieurs branches de la physique fondamentale grâce à des vidéos animées concises et faciles à comprendre ; cela inclut: la cinématique, la dynamique, la mécanique des fluides, la mécanique statique, les ondes et l'acoustique. En parallèle, les vidéos de scientifiques à l'action démontrent l'application de concepts associés à ces domaines dans des expériences de recherche classiques et originales réalisées dans des laboratoires modernes du monde entier.

Capillary Action in Thin Tubes

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