Surface Tension - What is the relation between angle of contact and surface tension?

  Surface Tension

Surface tension definition: The force of unity between the molecules of fluid gives rise to a phenomenon called surface tension. According to this aspect of molecular attraction, the free surface of the fluid always acts as if a thin membrane is spread over it and this membrane is tense and trying to contract. This is why a thin needle carefully placed on the surface of the water creates a small depression on the surface and its density stays there even if it is about eight times higher than the water. Then a clean glass tube of a small-bore is dipped in water, and the water rises in the tube, But when the tube is dipped in mercury, the mercury becomes depressed.

Surface tension equation or surface tension formula

                    T = F/L

• F is the force per unit length
• L is the length in which force act
• T is the surface tension of the liquid

Surface tension is measured as the force per unit length acting on both sides of the line in the equilibrium on the liquid surface, the direction of the force being tangential to the surface and perpendicular to the line. S.I. unit surface tension is measured in newton/meter. (N/m) and in CGS Unit dyn/cm.

Surface tension examples

• Insects walking on water.
• Floating a safety needle on the surface of the water.
• Rainproof tent materials where the surface tension of water will bridge the pores in the tent material.

Surface tension and surface energy

The force of attraction of the molecules present on the surface of a liquid towards each other is called the surface tension of that liquid. Surface energy is the uniform attractive force present between molecules on the surface of a solid material.

 The angle of contact: In a narrow tube, the free surface of liquid-like turpentine is concave and the surface of mercury is convex. The tangent plane inside a liquid is called the angle of contact between a liquid and a solid. Thus a is the contact angle between mercury and glass and b is the angle of contact between turpentine and glass. Note that a is obtuse while B is an acute angle. Generally, a wet glass contains all the liquids that have a sharp angle of contact. The force of surface tension acts in the direction of contact of the liquid with the solid, i.e. in the direction of the tangent plane on the liquid surface.

Surface tension and temperature

An increase in temperature increases the kinetic energy of molecules and decreases the effectiveness of intermolecular attraction, so surface tension decreases as temperature increases.

 Common Measurements 

surface tension of ethanol = 22.32 N/m

surface tension of water = 72 N/m

Let me know if you have more questions or if there is a specific topic that you would like to know more about.