Relation Between Viscosity And Density

Viscosity and Density

There is no direct relation between viscosity and density. However, both viscosity and density are affected by temperature. This implies, that for any given fluid, when the temperature is raised, the particles in it start to move apart, bringing down fluid density thereby the value of viscosity also falls down or fluid becomes less viscous.

In general, for any fluids, when the temperature is increased, its density decreases, thus the fluid becomes less viscous.

Kinematic Viscosity

In fluids, kinematic viscosity is the ratio of dynamic viscosity to density. Mathematically given by-

\(\begin{array}{l}\nu =\frac{\eta }{\rho }\end{array} \)

Where,

• ν is the kinematic viscosity.
• η is the dynamic viscosity / absolute viscosity.
• ρ is the density.

Refer to the table given below for definitions, units, and symbols for the above parameter.

	Definition	SI unit	Symbol
Kinematic Viscosity	The ratio of dynamic viscosity to density	m2/s	\(\begin{array}{l}\nu \end{array} \)
Dynamic Viscosity	The measure of internal resistance against the flow	Ns/m2	\(\begin{array}{l}\eta\end{array} \)
Density	The ratio of mass per volume	Kg/m3	\(\begin{array}{l}\rho\end{array} \)

Viscosity and Density of Water

The table given below gives the values of Viscosity and Density of water at 10⁰C and 20⁰C.

Temperature	100C	200C
Viscosity (mPa.s)	1.308	1.002
Density (g/m3)	0.99975	0.99804

Viscosity and Density of Air

The table given below gives the values of Kinematic Viscosity and Density of air at -10⁰C, -15⁰C and -20⁰C.

Temperature 0C	Density (Kg/m3)	Kinematic viscosity(m2/s)
-20	1.3958	1.1622×10-5
-15	1.3687	1.2039×10-5
-10	1.3426	1.2462×10-5

Hope you understood the relation between viscosity and density for a given fluid in fluid mechanics.

Physics Related Topics:

Relation Between Celsius And Fahrenheit

Relation Between Density And Temperature

Relation Between Pressure And Velocity

Relation Between Kp And Kc

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Frequently Asked Questions – FAQs

Q1

Define the density of the fluid.

Density is the measure of spaces between two particles in a given fluid.

Q2

Which parameter is used to measure the thickness of the fluid?

Viscosity is the parameter which is used to measure the thickness of the fluid.

Q3

How is kinematic viscosity represented.

Kinematic viscosity is represented by the formula:

\(\begin{array}{l}\nu =\frac{\eta }{\rho }\end{array} \)

Q4

Define dynamic viscosity.

The measure of internal resistance against the flow gives dynamic viscosity.

Q5

State true or false: In any fluid, when the temperature is increased, the density also increases.

False. When the temperature is increased, its density decreases and hence the fluid becomes less viscous.