Mechanical Properties of Fluids

Surface Tension

  • Work done per unit area in increasing the surface area of a film is known as surface energy.
  • Every liquid surface behaves like an elastic membrane and surface tension is a molecular phenomenon.
  • Surface tension can also be defined as the surface energy per unit surface area.
  • Angle of contact is the angle made by the tangent drawn to the liquid surface at the point of contact of solid liquid surface.
  • Angle of contact is not changed by the inclination of solid object in liquid.
  • The rise or fall of a liquid in a capillary called capilarity it is due to surface tension.
  • If the angle of contact is greater than 90° then the liquid does not wet solid and capillary depression takes place.
  • If the angle of contact is less than 90° then the liquid wets solid and capillary rise takes place.
  • Surface tension decreases with the increase of temperature.
  • Weakly soluble impurities decrease surface tension and highly soluble impurities increases surface tension.

Surface Tension View the Topic in this video From 23:01 To 1:01:20

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1. The property of a liquid by virtue of which it tries to acquire minimum surface area is called surface tension. It is given by surface tension, \tt S=\frac{F}{l}

2. Surface energy of a given liquid surface is equal to the work done against the force of surface tension, in forming the liquid surface of given area at a constant temperature.
Surface energy, E = S × ΔA