A ball of steel is dropped in a viscous medium draw its velocity time graph till it reaches the bottom.
A body when dropped in fluid travels with increasing velocity till it attains a maximum constant velocity called TERMINAL VELOCITY.
VTgraph.jpg
Once the ball is inside the viscous medium,
mg - Buoyant Force - Viscous Force = ma
mg - B - kv = ma
Since the acceleration is dependent on velocity, we have non-linear behaviour in v-t graph initially. The velocity would keep on increasing till terminal velocity is attained. The acceleration would be maximum initially, as there is no viscous force initially and would decrease with time due to increasing viscous force and eventually would become zero leading to terminal velocity. The above explanation assumes that there is enough depth allowing the attainment of terminal velocity.
