A small ball of mass m and density `rho` is dropped in a viscous liquid of density `sigma`. Ather some time the ball falls with a constant velocity. Calculate the viscous force acting on the ball.

Explanation

To solve the problem of calculating the viscous force acting on a small ball of mass \( m \) and density \( \rho \) that is dropped in a viscous liquid of density \( \sigma \), we follow these steps:

### Step 1: Understand the Forces Acting on the Ball
When the ball is dropped, it experiences two main forces:
1. The gravitational force (weight) acting downwards, given by \( F_g = mg \).
2. The viscous force acting upwards, which we need to calculate.

### Step 2: Establish Terminal Velocity Condition
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