What is Stoke.s law ? Define terminal velocity and calculate it for a spherical body moving vertically in a liquid and show that it is proportional to square of the radius of the spherical body.

Explanation

### Step-by-Step Solution

**Step 1: Define Stokes' Law**
Stokes' Law states that the viscous force \( F_v \) acting on a spherical object moving through a viscous fluid is directly proportional to the velocity \( v \) of the object, the viscosity \( \eta \) of the fluid, and the radius \( r \) of the sphere. Mathematically, it is expressed as:
\[ F_v = 6 \pi \eta r v \]
where:
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