5 Difference Between Cohesion And Adhesion In Fluid Mechanics

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What Is Cohesion?

Cohesive forces are the intermolecular forces such as those from hydrogen bonding and Van der Waals forces which cause a tendency in liquids to resist separation. These attractive forces exist between molecules of the same substance. For instance rain falls in droplets, rather than a fine mist, because water has strong cohesion which pulls its molecules tightly together, forming droplets. This force tends to unite molecules of a liquid, gathering them into relatively large clusters due to the molecules’ dislike for its surrounding.

What You Need To Know About Cohesion

  1. Cohesion is the attraction force between molecules of the same substance.
  2. Cohesion is responsible for surface tension such as droplets of water beading together on waxed paper.
  3. Cohesion is caused by hydrogen bonding and Van der Waals forces.
  4. A strong force of cohesion causes water droplets to form on any surface.
  5. Cohesion is an intermolecular force between different molecules.

What Is Adhesion?

Adhesive forces are the attractive forces between unlike molecules. They are caused by forces acting between two substances, such as mechanical forces (sticking together) and electrostatic forces (attraction due to opposing charges). In the case of a liquid wetting agent, adhesion causes the liquid to cling to the surface on which it rests. When water is poured on clean glass, it tends to spread, forming a thin, uniform film over the glasses surface. This is because the adhesive forces between water and glass are strong enough to pull water molecules out of their spherical formation and hold them against the surface of the glass, thus avoiding the repulsion between like molecules.

In slim tubes, cylinder or permeable substance ascension of liquids is usually due to adhesive and cohesive forces interacting between the liquid and the surface. This is referred to as capillarity or capillary action.

What You Need To Know About Adhesion

  1. Adhesion is the attractive force between two types of molecules, which are different from each other.
  2. Adhesion is responsible for a meniscus when water is observed in a glass container, because water clings to the glass around edges.
  3. Adhesion is caused by electrostatic or mechanical forces that exist among two kinds of different substances.
  4. A strong adhesion force causes a liquid to spread on a solid surface.
  5. Adhesion is an intermolecular force of attraction.

Also Read: Difference Between Laminar And Turbulent Flow

Difference Between Cohesion And Adhesion In Tabular Form

BASIS OF COMPARISON COHESION ADHESION
Description Cohesion is the attraction force between molecules of the same substance.   Adhesion is the attractive force between two types of molecules, which are different from each other.  
Effect Cohesion is responsible for surface tension such as droplets of water beading together on waxed paper.   Adhesion is responsible for a meniscus when water is observed in a glass container, because water clings to the glass around edges.  
Cause Cohesion is caused by hydrogen bonding and Van der Waals forces.   Adhesion is caused by electrostatic or mechanical forces that exist among two kinds of different substances.  
Effect On Water A strong force of cohesion causes water droplets to form on any surface.   A strong adhesion force causes a liquid to spread on a solid surface.  
Kind Of Force Cohesion is an intermolecular force between different molecules.   Adhesion is an intermolecular force of attraction.  

Summary

  • Attractive forces between molecules of the same type are called cohesive forces.
  • Attractive forces between molecules of different types are called adhesive force.
  • Cohesive forces between molecules cause the surface of a liquid to contract to the smallest possible surface area. This general effect is called surface tension.
  • Capillary action is the tendency of a fluid to be raised or suppressed in a narrow tube, or capillary tube which is due to the relative strength of cohesive and adhesive forces.