Surface tension is the property of a liquid which enables it to resist tensile stress. Surface tension is denoted by σ (sigma). Surface tension is expressed in N/m (Newton/meter).
Surface tension acts in the plane of the interface normal to any line in the surface.

A Newtonian fluid is one where there is a linear relationship between stress and strain-rate. The ratio of stress to strain-rate is the Viscosity of the fluid. A fluid where there is no linear relationship between stress and strain-rate is called a Non-Newtonian fluid.

Viscosity is also known as absolute viscosity or dynamic viscosity. Viscosity is defined as the property of a liquid which offers resistance to the movement of one layer of liquid over another adjacent layer of liquid. The viscosity of a liquid is due to cohesion and interaction between particles.