Water Movement in Soils: Ch. 1-Adhesion and Cohesion

Decagon Devices, Inc.

10 Sept 201501:50

Summary

TLDRThe video explains the principles of capillarity, demonstrating how water moves upward in porous materials due to adhesive and cohesive forces. In the first demonstration, water rises into a ceramic rod from a dish because of attraction between the rod's surface and water molecules. This creates tension, as pressure in the water above the free surface is lower than atmospheric pressure. The second demonstration shows water rising between two closely spaced glass plates, with similar forces at play, emphasizing how tighter spacing increases the height of the water's rise due to internal tension.

Takeaways

🧪 The glass plates are one foot high and two feet wide with a half-inch space between them, representing a vertical cross-section through the soil.
🌊 Capillarity is demonstrated through the movement of water into dry, coarse materials due to adhesive and cohesive forces.
📉 Liquid is pulled upward from free water into a porous ceramic rod because of the attraction between the water molecules and the ceramic's surface.
🌍 Cohesion (between water molecules) and adhesion (between water and solid surfaces) allow water to move against gravity.
💧 The pressure in water inside the ceramic rod, above the free water level, is lower than atmospheric pressure, creating tension.
📊 In another demonstration, water rises between two closely spaced glass plates because of the adhesive force between water and glass.
📏 The height of water rise is greater when the plates are closer together, enhancing the adhesive forces.
🔽 The pressure in water that rises above the free water surface is less than atmospheric pressure, again referred to as tension.
⬆️ The higher the water rises, the greater the internal tension created within the water column.
🔬 Both demonstrations illustrate how capillarity works, a critical principle for water movement in soils and porous materials.

Q & A

What is the main concept discussed in the script?
-The script discusses the principles of capillarity and how adhesive and cohesive forces allow water to move against gravity, particularly in soil and between glass plates.
What does the model with glass plates represent?
-The model with glass plates represents a vertical cross-section through soil, used to demonstrate the principles of capillarity.
How does water move into dry, coarse materials in the first demonstration?
-In the first demonstration, water moves into dry, coarse materials through a porous ceramic rod due to the adhesive forces between water and the rod’s surface and the cohesive forces between water molecules.
What is the role of adhesive and cohesive forces in capillarity?
-Adhesive forces cause water to stick to surfaces like glass or the ceramic rod, while cohesive forces make water molecules attract each other. Together, these forces allow water to move upward against gravity.
What is meant by 'tension' in the context of the first demonstration?
-In the first demonstration, 'tension' refers to the condition where the pressure in the water contained in the ceramic rod is less than atmospheric pressure, which helps move water upward.
How does the second demonstration show the effect of adhesive forces?
-In the second demonstration, water rises between two closely spaced glass plates because of the adhesive forces between the glass and water, along with cohesive forces between water molecules.
What happens to the pressure of water above the free water surface in both demonstrations?
-In both demonstrations, the pressure of water above the free water surface is less than atmospheric pressure, creating tension that allows water to rise.
Why is the height of water rise greater when the glass plates are closer together?
-The height of water rise is greater when the glass plates are closer together because the adhesive forces between the glass and water are stronger when the spacing is tighter, enhancing capillary action.
What is the significance of free water in the dish in the first demonstration?
-The free water in the dish serves as the source from which water is pulled upward into the porous ceramic rod due to capillary action and the adhesive and cohesive forces at play.
How do adhesive and cohesive forces allow water to move against gravity?
-Adhesive forces cause water to stick to solid surfaces like glass or ceramic, while cohesive forces keep water molecules together. Together, these forces create upward movement of water, overcoming the downward pull of gravity.

Outlines

00:00

🌊 Water Movement through Soil via Capillarity

The paragraph explains how water moves through soil due to the principle of capillarity. It describes a demonstration involving a ceramic rod and how liquid is pulled upward from free water into the rod because of adhesive forces (the attraction between water and mineral surfaces) and cohesive forces (the attraction between water molecules). These forces work together to counteract gravity and move the water upwards, creating a pressure lower than atmospheric pressure in the water, known as tension.

🧪 Capillary Action between Glass Plates

This paragraph describes a second demonstration, illustrating how water rises between two closely spaced glass plates due to adhesive forces between glass and water and cohesive forces between water molecules. The height of the water rise is greater when the glass plates are closer together. This rise creates internal tension, as the water pressure above the free water surface is lower than atmospheric pressure. The internal tension increases with the height of the water rise.

Mindmap

Keywords

💡Capillarity

Capillarity refers to the movement of liquid in narrow spaces without the assistance of external forces like gravity. In the video, this principle explains how water rises into dry, porous materials and moves against the force of gravity. For example, capillarity is demonstrated by the upward movement of water into a porous ceramic rod from a free water source.

💡Cohesion

Cohesion is the force that causes water molecules to stick together. In the video, cohesive forces are responsible for the upward movement of water as water molecules pull on each other. This principle supports the capillarity phenomenon by enabling water to rise between closely spaced glass plates.

💡Adhesion

Adhesion is the attraction between water molecules and the surfaces of different materials. In the video, adhesive forces between water and the surfaces of glass plates or the ceramic rod allow the water to be pulled upward into these materials. Adhesion plays a crucial role in capillarity by enabling water to climb materials like glass and ceramic.

💡Porous Materials

Porous materials contain small openings or pores that allow liquids to pass through. In the video, the ceramic rod acts as a porous material, allowing water to be absorbed and rise through it. These materials are critical to understanding how water can move through the soil and other substances.

💡Tension

Tension refers to the condition where the pressure in water is less than atmospheric pressure. The video demonstrates this concept when water rises into porous materials or between glass plates, creating internal tension as water moves against gravity. Tension is key to understanding the mechanics behind water rising above a free water surface.

💡Free Water

Free water is the body of water that serves as the source from which water is drawn into porous materials. In the video, water is pulled upward from a dish of free water into the ceramic rod and glass plates. This is the starting point for capillary action to occur.

💡Gravitational Force

Gravitational force is the downward pull that objects experience due to the Earth’s gravity. In the video, water moves against this downward pull due to capillarity, with the adhesive and cohesive forces allowing water to rise in opposition to gravity.

💡Glass Plates

The glass plates in the video represent the surfaces between which water rises. They are used in a demonstration of capillarity, illustrating how the adhesive forces between water and glass, combined with cohesion between water molecules, allow water to move upward. The closer the plates are, the higher the water rises.

💡Ceramic Rod

The ceramic rod is a porous material used in the first demonstration in the video to show capillarity. Water is drawn into the rod from a dish of free water due to adhesive and cohesive forces, providing a visual example of how porous materials can pull water upward.

💡Atmospheric Pressure

Atmospheric pressure is the pressure exerted by the weight of the atmosphere. In the video, the pressure inside the water that rises through the ceramic rod and between the glass plates is less than the atmospheric pressure. This difference in pressure is a key factor in the concept of tension and the ability of water to rise above the free water surface.

Highlights

The glass plate is a foot high and two feet wide with about one-half inch of space between.

The model represents a vertical cross-section through the soil.

The demonstration illustrates the principle of capillarity, where water moves into dry, coarse materials.

Water is pulled upward from free water into a porous ceramic rod due to the attraction of soil minerals to water.

The cohesive and adhesive forces are responsible for moving water upward against gravity.

The pressure in the water inside the ceramic rod above the free water level is lower than atmospheric pressure, causing tension.

In the second demonstration, water rises between two closely spaced glass plates.

The rise occurs due to adhesive forces between the glass and water and cohesive forces between water molecules.

The height of water rise is greater when the glass plates are closely pitched together.

The pressure in the water above the free water surface is less than atmospheric pressure.

This reduced pressure in the water is again referred to as tension.

Capillarity is a critical concept for understanding how water moves through soil and porous materials.

The internal tension in the water increases as the height of the water rise increases.

Adhesion refers to the attraction between water molecules and other surfaces, such as glass or soil particles.

Cohesion is the attraction between water molecules themselves, enabling water to resist external forces like gravity.