M-EngMom8: Conservation of energy; example : ball in funnel.

PIRA: Unknown

Equipment: large funnel (glass) mounted vertically in wood base, pingpong ball. The items are locate in Set 8, Cabinet 2, Shelf 2.

Procedure: "Hold the wood base firmly against the table top and start the ball rolling around the inside of the funnel parallel to the rim as near the rim as you can. This can most easily be done by rolling the fingers over the top of the ball in the direction you wish it to circulate while maintaining the ball in contact with the inner surface of the funnel. Some demonstrators prefer to have a strip of emery cloth about 1" x 3" affixed to the inside of the funnel just inside the rim with long dimension parallel to the rim. This may help to get the ball rolling. If the start is not vigorous enough the ball will execute an elliptical course descending into the funnel and coming back up to near the rim. If the start is too vigorous the ball flies out of the funnel entirely. When the course lies satisfactorily within the funnel and not too elliptical, it is incredible how much time is required for the ball to settle down to rest at the bottom of the funnel.

"There are many similarities here to orbital motion of a satellite about its primary body though the potential situation is quite different. As kinetic energy is abstracted from the ball (by windage, friction, noise) dynamics demands that the ball move down into the funnel. This, however, converts potential energy into kinetic energy of the ball. Hence, much more mechanical energy has to be abstracted before the ball ‘dies’ than one's intuition leads him to expect." — Percy Carr (1970)