Short Answer

Cohesion is the force of attraction between particles of the same substance. For example, water drops stick together because of cohesion. Adhesion is the force of attraction between particles of different substances. For example, water sticking to glass is due to adhesion.

These two forces help explain many natural events such as the formation of water droplets, capillary action, and how liquids spread on surfaces. They play an important role in physics, biology, and everyday life.

Detailed Explanation :

Cohesion and adhesion

Cohesion and adhesion are two important forces that describe how particles of matter attract each other. These forces help us understand the behaviour of liquids and how they interact with surfaces. Many common activities—such as drops forming on leaves, water climbing inside thin tubes, or paint spreading on walls—are possible because of these forces. Although cohesion and adhesion are simple ideas, they play a major role in physics, chemistry, and biology.

Cohesion

Cohesion is the force of attraction between particles of the same substance. This means that molecules of a material stick to each other because of this force. Cohesion is usually strong in liquids, especially in water. Water molecules attract each other due to hydrogen bonding, which creates strong cohesive forces.

Some important effects of cohesion:

1. Formation of water droplets
   When water falls on a surface or is dropped from a tap, it forms rounded droplets. This happens because water molecules pull each other tightly, creating a spherical shape.
2. Surface tension
   Cohesion is responsible for surface tension in liquids. Surface tension is a property where the surface of a liquid acts like a stretched elastic sheet. This is why insects such as water striders can walk on water and why small objects like needles can float when placed gently on the water surface.
3. Limiting the spread of liquids
   Because of strong cohesive forces, some liquids do not spread easily. For example, water forms beads on a waxed surface because the molecules hold tightly to each other.

Cohesion varies for different substances. Liquids with stronger cohesive forces, like water, show higher surface tension, while liquids with weak cohesion, like alcohol, spread more easily and evaporate faster.

Adhesion

Adhesion is the force of attraction between particles of different substances. This force causes one substance to stick to another. Adhesion is very important in explaining how liquids behave when they come in contact with solid surfaces.

Examples of adhesion in daily life:

1. Water sticking to glass
   When you pour water into a glass and then empty it, small drops remain stuck to the walls. This happens because water molecules are attracted to glass molecules more strongly than to each other.
2. Ink or paint on surfaces
   Paint spreads on a wall because of adhesion between paint particles and wall surface. Similarly, ink sticks to paper because of adhesive forces.
3. Wet cloth sticking to a surface
   When a cloth is wet, it sticks easily to tables, walls, or windows due to adhesion between water and the surface.

Adhesion can be stronger or weaker depending on the types of substances involved. Surfaces like glass, paper, or cloth show strong adhesion with water, while surfaces like plastic or wax show weak adhesion.

Interaction between cohesion and adhesion

Cohesion and adhesion often work together and influence how liquids behave. One important example is capillary action. Capillary action is the tendency of a liquid to rise or fall in a narrow tube. It happens because adhesion pulls the liquid up the walls of the tube, while cohesion pulls the rest of the liquid along with it. This process is essential for many natural and scientific activities.

Examples of capillary action:

• Plants use capillary action to transport water from roots to leaves.
• Ink moves through the nib of a fountain pen by capillary action.
• Paper towels absorb water because water climbs between the tiny fibres.

The shape of a liquid surface inside a container is also decided by cohesion and adhesion. Water forms a concave meniscus (curved upward at the edges) because adhesion to glass is stronger than cohesion among water molecules. Mercury, on the other hand, forms a convex meniscus (curved downward) because cohesion is stronger than adhesion.

Importance of cohesion and adhesion

These forces have great importance in nature and technology:

• In plants, water movement through stems depends on these forces.
• In industries, paints, inks, adhesives, and dyes work because of adhesion.
• In daily life, cleaning, wiping, and even cooking involve these forces.
• In science, they help explain surface tension, liquid flow, and molecular interactions.

Both forces are essential in understanding how materials behave and interact at the microscopic level.

Conclusion

Cohesion and adhesion are attractive forces that determine how substances stick together or stick to other materials. Cohesion works between similar particles, while adhesion works between different particles. These forces help explain surface tension, capillary action, droplet formation, and many natural and practical processes. Understanding cohesion and adhesion helps us better understand how liquids behave in daily life and in scientific applications.