Origin of Surface Tension

Cohesive forces:
- Cohesive forces are the attractive forces between molecules of the same substance.
- These forces arise due to intermolecular interactions, such as van der Waals forces, hydrogen bonding, and dipole-dipole interactions.
- Cohesive forces hold the molecules of a liquid together, creating a strong bond between them.
- These forces are responsible for the phenomenon of surface tension.

Adhesive forces:
- Adhesive forces are the attractive forces between molecules of different substances.
- These forces arise due to intermolecular interactions between the molecules of a liquid and the molecules of another substance.
- Adhesive forces can be observed when a liquid forms a meniscus in a glass tube or when a liquid wets a solid surface.
- These forces also contribute to the origin of surface tension.

Surface Tension:
- Surface tension is the property of a liquid that allows it to resist external forces and minimize its surface area.
- It is caused by the cohesive forces between the molecules at the surface of a liquid.
- The molecules in the bulk of the liquid experience cohesive forces in all directions, resulting in a net force of zero.
- However, the molecules at the surface experience a net inward force due to the lack of molecules above them.
- This inward force causes the surface to behave like a stretched elastic sheet, leading to the formation of a thin film on the surface.
- The surface tension is directly proportional to the strength of the cohesive forces between the molecules.

Contribution of Cohesive and Adhesive Forces:
- Both cohesive and adhesive forces contribute to the origin of surface tension.
- Cohesive forces hold the molecules of a liquid together, creating a strong bond between them, which is essential for surface tension.
- Adhesive forces allow a liquid to interact with other substances, such as a solid surface or a glass tube, and form a meniscus or wet the surface.
- These interactions between the liquid and other substances involve both cohesive and adhesive forces, which collectively contribute to the surface tension of the liquid.
- Without cohesive forces, there would be no intermolecular attractions to create surface tension.
- Without adhesive forces, a liquid would not be able to interact with other substances and exhibit surface tension-related phenomena.
- Therefore, both cohesive and adhesive forces are necessary for the origin and existence of surface tension in liquids.