Originally Posted by
JPradun
Experiment: take off the front wheel and hold it by the skewer in both hands. Spin the wheel really fast and try to move the wheel from vertical to horizontal (90 degrees). It's that "force."
+1 here are some nice demonstrations:
http://www.youtube.com/watch?v=545GwnupKAE
http://www.youtube.com/watch?v=u47eMRgJoBQ