Centripetal; center seeking Centrifugal; center fleeing

The book has a diagram on pages 128 and 129 with a bug in a can attached to a string that is being hurled around in a circular motion creating both forces. The centripetal foce is the string acting on the can with bug. While the centrifugal force is pulling on the bug away from the hand. It shows the bug standing able to walk imitating gravity.

These two forces one day could be used to resemble gravity in a space station. The outside ring of the station would equal one full g of gravity equal to that of the earth's. As one would get closer to the center of the space station gravity would continue to reduce until one met the center where the gravity would equal 0 g's.