Table of contents | |
Viscosity | |
Variation of Viscosity | |
Poiseuille’s Formula | |
The Rate of Flow of Liquid | |
Stoke's Law |
Viscosity
The viscosity of liquids decreases with increase in temperature
where, η0 and ηt is are coefficient of viscosities at 0°C and t°C, α and β are constants.
The viscosity of gases increases with increase in temperatures as
η ∝ √T
The viscosity of liquids increases with increase in pressure but the viscosity of water decreases with increase in pressure.
The viscosity of gases do not changes with pressure.
The rate of flow (v) of liquid through a horizontal pipe for steady flow is given by
where, p = pressure difference across the two ends of the tube. r = radius of the tube, n = coefficient of viscosity and 1 = length of the tube.
Rate of flow of liquid through a tube is given by
v = (P/R)
where, R = (8 ηl/πr4), called liquid resistance and p = liquid pressure.
When a sphere moves through a thick liquid, like honey, the resistance it faces depends on how fast it's moving, how big the sphere is, and how thick the liquid is. This resistance is called Stokes' drag.
Imagine stirring honey with a spoon—the harder and faster you stir (velocity), the bigger the spoon (radius), and the thicker the honey (viscosity), the more resistance you feel.
Illustration of Stoke's Law
This resistance force is calculated using a formula that takes into account the viscosity of the liquid, the size of the sphere, and how fast it's moving.
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1. What is viscosity and how is it related to the rate of flow of liquid? |
2. How does viscosity vary with temperature? |
3. What is Poiseuille's formula and how is it used to calculate the rate of flow of liquid in a pipe? |
4. How does Stokes's Law relate to viscosity? |
5. How can viscosity be measured experimentally? |
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