Typically, the viscosity of a fluid depends on the molecular interactions or associations that can form during the movement of the molecules forming the fluid. Therefore, the motion of a fluid is usually the result of the sliding of the fluid layers over each other.

• It is important to remember that the higher the viscosity, the thicker the fluid.

In short, there are two types of viscosity: dynamic viscosity and kinematic viscosity. Briefly, regardless of the type of viscosity, they are generally expressed in terms of the quantity displaced in a defined time.

The Dynamic Viscosity

The dynamic viscosity is used to measure the internal resistance of the fluid against the flow. It is to say that this type of viscosity communicates information about the force required to allow a fluid to flow at a certain speed.

When we think of dynamic viscosity, several methods can be used to express it, but the expression recognized by the International System is the Pascal second (Pa.s) or the Poiseuille (Pl).

• The Poiseuille or Pascal second is a data that expresses the movement of 1 gram of fluid in metres.
  
  

Kinematic viscosity

Kinematic viscosity refers to the relationship between viscosity and density of the fluid. This means that kinematic viscosity expresses the speed at which a fluid move when a certain force is applied to it. The International System does not have a precise term to define it, but the standard is to use m2/s.

The Viscosity of Water

As with all other types of fluids, the temperature of said fluid will have an impact on its viscosity. Typically, an increase in the temperature of a fluid means a decrease in its viscosity. This is mainly due to the increase in kinetic energy, which leads to an increase in the mobility of the molecules.

Viscosity of water according to temperature

• - The mPas.s represents a millipascal second.
• 1 mPa.S = 0.001 Pa.s = 0.001 kg/m-s