Units of Surface Tension

Surface tension is the tendency of liquid surfaces to behave as stretched membranes due to the cohesive forces between molecules. It causes phenomena like water striders walking on water.

Si unit of surface tension

The SI (International System of Units) unit of surface tension is Newton per meter (N/m). Surface tension is a measure of the force per unit length acting perpendicular to a line on the liquid surface. In terms of units, it is expressed as the force (measured in Newtons) divided by the length (measured in meters). Therefore, the SI unit of surface tension is N/m.

CGS unit of surface tension

  • The cgs unit of surface  tension is dynes per centimeter (dyn/cm).
  • Not an SI unit but commonly used historically.
  • Defined as 1 dyn/cm = 0.001 N/m.

erg/cm2

  • Surface tension may be given in ergs per square centimeter (erg/cm^2).
  • Related to dyn/cm: 1 erg/cm2 = 1 dyn/cm
  • Converts to other units as: 1 erg/cm2 = 0.001 mN/m

mN/m

  • Surface tension is often given in millinewtons per meter (mN/m) for low values.
  • Defined as 1 mN/m = 0.001 N/m
  • Useful for organic liquids like ethanol or oils.
SI unitNewtons per meter (N/m)
CGS unitdynes per centimeter (dyn/cm)
Formula for surface tension (T)T = F​/l
where (T) is surface tension, ( F ) is the force, and ( L ) is the length along which the force is acting.
Dimensional formula of surface tensionThe dimensional formula of surface tension (T) is expressed as:
[M T-2 L-1]
where ( M ) represents mass and ( T ) represents time.

Converting Between Units

Use conversion factors to convert between units:

  • dyn/cm to N/m: multiply by 0.001
  • erg/cm^2 to mN/m: multiply by 0.001
  • mN/m to dyn/cm: multiply by 1000.

FAQs

What is the SI unit of surface tension?

The SI unit of surface tension is Newton per meter (N/m) or equivalently, Joule per square meter (J/m²).

Why is surface tension measured in Newton per meter?

Surface tension is essentially a force acting along the perimeter of a unit length on the liquid surface. In SI units, force is measured in Newtons (N), and length is measured in meters (m), so the unit becomes N/m.

How is surface tension measured experimentally?

Surface tension is often measured using techniques like the capillary rise method or the drop weight method. These methods involve measuring the force or weight acting on a liquid due to surface tension.

Can surface tension vary for different liquids?

Yes, surface tension can vary for different liquids and is influenced by factors such as molecular structure, temperature, and the presence of impurities

What are typical values for surface tension?

Surface tension values vary widely for different liquids. For example, water has a surface tension of about 0.072 N/m at room temperature, while liquid mercury has a much higher surface tension of about 0.48 N/m.

How does temperature affect surface tension?

In general, surface tension decreases with an increase in temperature. This is because higher temperatures tend to weaken the cohesive forces between liquid molecules.

What are some practical applications of understanding surface tension?

Surface tension plays a crucial role in various phenomena, including capillary action, formation of droplets, and the behavior of liquids in different types of containers. Understanding surface tension is important in fields such as physics, chemistry, biology, and engineering.

Is surface tension only applicable to liquids?

While surface tension is most commonly associated with liquids, it can also be observed at the interface between liquids and gases. For example, the surface tension of the air-water interface affects the behavior of bubbles and aerosols

How is surface tension related to wetting and spreading of liquids on surfaces?

Surface tension influences the wetting behavior of liquids on solid surfaces. The contact angle between a liquid and a solid surface is related to surface tension, and it determines whether the liquid will spread or bead up on the surface