Loop of death
Place the ball in any point of the inclined plane and let it fall. Observe the motion of the ball. Try to find a starting point that will make the ball:
1. Rise to a certain height in the loop and then roll down.
2. Fall from the top part of the loop.
3. Ride the whole loop.
How does it work
There are two forces acting upon the ball in the loop: gravity (directed vertically down) and centrifugal force (directed outwards from the loop). Riding the whole loop is possible if at the top point the magnitude of centrifugal force acting on the ball exceeds the magnitude of gravity. The magnitude of centrifugal force depends on the mass of the ball, the radius of the loop (these values are constant) and the ball speed squared. Hence, the rolling ball needs sufficient speed to ride the whole loop.
Described effect is put into practice in funfairs in roller coaster operation.