Final answer:
Terminal velocity aids in understanding how both passages explore the concept of reaching a maximum or limiting speed, which is a steady state where the acceleration of a falling object becomes zero.
Step-by-step explanation:
The concept of terminal velocity helps in understanding the shared central idea of Passages A and B by illustrating the maximum speed achievable, which is a concept explored in both passages. Terminal velocity refers to the condition when the acceleration of a falling object becomes zero because the force of gravity is balanced by the viscous drag force and any buoyant force present. This concept is significant because it represents a limiting value, similar to other physical concepts where a system reaches a steady state or limit. The passages might use this idea to explore limits or endpoint conditions in various contexts.