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Understanding Surface Tension and Its Effects

Aug 13, 2024

Lecture Notes: Surface Tension and Related Concepts

Surface Tension

  • Definition:

    • Surface tension is a property of the surface of a liquid that allows it to resist external force.
    • It is due to the cohesive forces among liquid molecules.
  • Example:

    • A needle can rest on the surface of water due to surface tension.
    • It is not floating but supported by the tension.
  • Cause:

    • Water molecules are attracted to each other, forming hydrogen bonds (cohesion).
    • Molecules on the surface have fewer neighbors, allowing them to form tighter bonds, leading to surface tension.

Cohesion

  • Definition:

    • The attraction between like molecules.
    • In liquids, it leads to the molecules being pulled together.
  • Effect on Surface Tension:

    • Molecules in the bulk are restricted by surrounding molecules.
    • Surface molecules are less restricted, forming tighter, cohesive bonds.

Practical Applications of Surface Tension

  • Bile in Urine Test:

    • Surface tension is lowered by bile, indicating liver function.
  • Camping and Tents:

    • Do not touch the inside surface of a rain-covered tent to prevent breaking surface tension and allowing water leakage.
  • Washing Hands:

    • Detergents reduce surface tension, allowing water to spread more easily, cleaning better.

Adhesion

  • Definition:

    • The attraction between different substances, such as water and container walls.
  • Meniscus Formation:

    • The curved surface of a liquid in a container is due to adhesion.
    • The adhesive force pulls water up the sides of the container.

Capillary Action

  • Definition:

    • The ability of a liquid to flow in narrow spaces without the assistance of external forces.
  • Mechanism:

    • Arises due to adhesion between the liquid and the walls of the container.
    • The smaller the diameter of the tube, the higher the rise of the liquid.
  • Importance:

    • Significant in biological systems and other practical scenarios.