# Anomaly in viscous force - vs - velocity relationships

It is well known that the viscous force (or drag force) is directionally proportional to the square of the velocity in many cases. For example the torque on motors driving a fan-type load (pump) is proportional (approximately) to the square of the rotational speed. The air drag force on a car or a plane has a similar relation between linear drag force and straight line velocity.

However in a mass-spring-damper system common in mechanics and control theory, the viscous force F is proportional to the velocity itself, as in the relation is F = -Bv, where v is the velocity and B is the viscous damping constant.

What is the reason for such an anomaly? Are they for different conditions/situations? If so, how? Or am I missing something entirely here?