Cohesive Force: Definition and Characteristics Explained with Real-Life Examples

Have you ever noticed how water forms droplets on a leaf or how some insects can walk on the surface of water? These interesting phenomena occur because of cohesive force. Cohesive force is the attraction between molecules of the same substance, causing them to stick together. It plays an important role in many natural processes, from the formation of raindrops to the movement of water in plants.

This article covers the cohesive force, how it differs from adhesive force, its role in liquids and surface tension, and its everyday applications. 

Table of Contents 

• What is Cohesive Force
• What is Cohesive Force in Liquids
• Examples of Cohesive Force
• How the Surface Tension and Cohesive Force Relates
• Factors Affecting Cohesive Force
• Applications of Cohesive Force

What is Cohesive Force?

Cohesive force is the force of attraction between molecules of the same substance. In simple words, it is the tendency of similar molecules to stick together due to intermolecular attraction.

For example, water molecules attract one another through hydrogen bonding, which is why water forms droplets instead of spreading out completely.The word cohesion comes from the Latin word cohaerere, which means to stick together.

Definition

Cohesive force is the intermolecular force of attraction that exists between molecules of the same kind.

Examples include:

• Water molecules attracting other water molecules
• Mercury molecules sticking together
• Oil molecules attracting each other

The Question is: How Cohesive Forces differs from Adhesive

Students often confuse cohesive and adhesive forces because both involve molecular attraction. However, they are different.

• Cohesive force: Attraction between molecules of the same substance.
• Adhesive force: Attraction between molecules of different substances.

For example:

• Water sticking to water → Cohesion
• Water sticking to glass → Adhesion

Both forces work together in many natural processes, including capillary action and the movement of water through plants.

Read More: Atoms and Molecules 

What is Cohesive Force in Liquids

Cohesive force is especially important in liquids because the molecules are free to move while still remaining close to one another.

Among common liquids, water has one of the highest cohesive forces due to the presence of hydrogen bonds between its molecules.

Because of cohesion:

• Water forms droplets.
• Liquids tend to minimise their surface area.
• The surface of water behaves like a stretched elastic membrane.
• Liquids can remain together in containers.

Inside a liquid, molecules are surrounded by other molecules on all sides, so the forces balance out.

However, molecules on the surface experience an inward pull because there are no molecules above them. This inward pull creates surface tension.

Have you ever wondered Why Does Water Have High Cohesive Force?

Water molecules are polar.

Each water molecule contains:

• A slightly positive hydrogen end (δ⁺)
• A slightly negative oxygen end (δ⁻)

Because opposite charges attract each other, neighbouring water molecules form hydrogen bonds.

These hydrogen bonds are responsible for water's high cohesive force.

Examples of Cohesive Force

1. Formation of Water Droplets: Rainwater forms droplets because water molecules attract one another.
2. Mercury Forms Spherical Drops: Mercury has very strong cohesive forces, causing it to form round beads.
3.  Water Striders Walking on Water:Some insects can walk on water because cohesive forces create strong surface tension.
4. Dew Drops on Leaves:Morning dew remains in the form of droplets due to cohesion.
5. Raindrop Formation: Tiny water molecules combine because of cohesive forces and eventually form raindrops.

How the Surface Tension and Cohesive Force Relates?

Surface tension is the tendency of the surface of a liquid to shrink to the smallest possible area due to cohesive forces.

Because surface molecules are pulled inward, the surface behaves like a thin elastic sheet.

Surface tension is responsible for:

• Formation of spherical water droplets
• Floating of small insects on water
• Formation of soap bubbles
• Capillary action in plants

Factors Affecting Cohesive Force

Several factors affect the strength of cohesive forces.

Nature of the Substance:Polar substances generally exhibit stronger cohesive forces than non-polar substances.

Temperature: As temperature increases, molecular motion increases and cohesive forces become weaker.

Intermolecular Forces:Substances with stronger intermolecular forces have greater cohesion.

Molecular Structure:The arrangement and polarity of molecules determine the strength of cohesion.

Applications of Cohesive Force

Cohesive force has many practical applications in daily life and science.

1. Formation of Raindrops: Water molecules combine due to cohesion.
2. Water Transport in Plants: Cohesive forces help water molecules move upward through xylem vessels.
3. Cleaning and Washing: Detergents reduce cohesive forces, allowing water to spread more easily.
4. Ink Flow in Pens: Cohesion helps maintain a continuous flow of ink.
5. Biological Systems:Cohesion plays an important role in blood flow and water transport in living organisms.
6. Industrial Applications:Used in paints, coatings, printing technologies and liquid handling systems.

We have learned that Cohesive force in chemistry is the attractive force between molecules of the same substance that causes them to stick together. It is responsible for many everyday phenomena, such as the formation of water droplets, surface tension and the movement of water in plants.