## Liquid surface properties

Liquid surface properties are defined here:

### Surface film

It is the top most layer of liquid at rest with thickness equal to molecular range.

### Surface tension

1) It is the property of the liquid by virtue of which the free surface of the liquid at rest tends to have the minimum surface area and as such it behaves as if covered with a stretched membrane.
2) Quantitatively, surface tension of a liquid is measured as the force acting per unit length of a line imagined to be drawn tangentially anywhere on the free surface of the liquid at rest. It acts at the right angle to this line on both the sides and along the tangent to the liquid surface. i.e. S = F/l
3) Surface tension of a liquid is also defined as the amount of work done in increasing the free surface of liquid at rest by unity at constant temperature. i.e. S= W/A
4) Surface tension is molecular phenomena and it arises due to electromagnetic forces. The explanation of surface tension was first given by Laplace.
5) Surface tension is a scalar quantity as it has no specific direction for a given liquid.
6) Surface tension does not depend upon the area of the free surface of liquid at rest.

### Viscosity

1) Viscosity is the property of a fluid (liquid or gas) by virtue of which an internal frictional force or viscous drag comes into play when the fluid is in motion and opposes the relative motion of its different layers.
2) The coefficient of viscosity of liquid is defined as the tangential force ( = backward viscous drag) required to maintain a unit viscosity gradient between two layers of liquid each of unit area.
3) The value of viscosity and compressibility for ideal liquid is 0.
4) Viscosity is due to transport of momentum.