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Question
Write down the expression for Stoke’s force and explain the symbols involved in it.
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Solution
The viscous force F acting on a spherical body of radius r depends directly on:
- radius (r) of the sphere
- velocity (v) of the sphere and
- coefficient of viscosity η of the liquid
`["MLT"^-2] = "k"["ML"^-1"T"^-1]^"x" xx ["L"]^"y" xx ["LT"^-1]^"z"`
On solving, we get x = 1, y = 1 and z = 1.
Therefore, F = kη rv
Experimentally, Stoke found that the value of k = 6π
F = 6πη rv
This relation is known as Stoke’s law.
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