Final answer:
Rack and pinion elevators can move with a constant velocity and are not required to be accelerating. They can maintain a uniform speed in either upward or downward direction.
Step-by-step explanation:
The characteristic that does not describe a rack and pinion elevator system is:
- The elevator must be accelerating upward.
- The elevator must be accelerating downward.
Rack and pinion elevators can move with a constant velocity, either going upward or downward. These elevators have a gear system that allows them to maintain a uniform speed whether they are moving up or down, which is contrary to the idea that they must be accelerating. Rack and pinion systems can indeed accelerate or decelerate, but they are not defined by the requirement to be accelerating in either direction.