# What is viscosity

Hello,

What is fluid viscosity?

Thank you.

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• Posts: 3,603Forum Coordinator

Viscosity is the measure of the fluid resistance to deformation. When fluids move they tend to deform continuously. This is due to some internal forces (or better stresses) that we can call shear stresses. For some fluids, the deformation is proportional to the magnitude of the shear stresses. These fluids are known as 'Newtonian Fluids'. The SI units of viscosity are kg / (m s) or (Pa s).

Have a look at our Ansys Innovation Courses. In particular you check out these two courses that discuss about viscosity:

• Thank you for the response! Why are there two types of viscosities? How do you differentiate between them?

Thank you!

• Posts: 3,603Forum Coordinator

Hi @prajput , the definition provided by my colleague is for the dynamic viscosity of the fluid. When you divide this number with the fluid density, you will obtain the kinematic viscosity.

Mathematically,

nu = mu / rho

where,

nu refers to kinematic viscosity,

mu refers to dynamic viscosity, and

rho refers to fluid density

The SI unit is m^2/s.

Thank you.?