Once again, picture in your mind a round world. Now imagine that there are two people on this world, one at each pole. For the person at the top of the world, (the North Pole), gravity is pulling him down, towards the South Pole. But for the person at the South Pole, shouldn't gravity pull him down as well? What keeps our person at the South Pole from falling completely off the face of the "globe"?
http://www.alaska.net/~clund/e_djublonskopf/Flatearthsociety.htm