A cylindrical habitat in space 6.00 km in diameter and 30 km long has been proposed (by G. K. O’Neill, 1974) Such a habitat would have cities, land, and lakes on the inside surface and air and clouds in the center. This would all be held in place by rotation of the cylinder about its long axis. How fast would the cylinder have to rotate to imitate the Earth’s gravitational field at the walls of the cylinder?