Q. In designing rotating space stations to offer for artificial-gravity environments, one of the constraints that must be considered is motion sickness. Studies have shown that the negative effects of motion sickness begin to appear while the rotational motion is faster than approximately 2.05 revolutions per minute. On the other hand, the magnitude of the centripetal acceleration at the astronauts' feet must equal the magnitude of the acceleration because of gravity on earth. Thus, to eliminate the difficulties with motion sickness, designers must choose the distance between the astronaut's feet and the axis about which the space station rotates to be greater than a certain least value. What is this least value?