On The U of Az campus today is a small merchant fair
including shows by rollerbladers in a big (10-12 meters
across) U shaped surface. At the peak of the U, the skaters
could either turn around and go back down or land on a
platform. How can that be, since at its top the U appears
to be going straight up. A marble in a similar track would
head right back down and could not land on the platform.
Could it be the motion of the skaters Center of
Momentum is not the same as the skates?