Fiddlesticks is a demonstration that shows the transfer of potential energy into rotational kinetic energy. Slide the rubber grommets to the top of the rod and give them a slight spin. You will see that as the grommets spin increases their rate of fall will decrease and vice versa. Another way to use this to show energy transfer is to only let the bottom grommet start spinning down the rod. Then let the top grommet which has no spin fall onto the bottom grommet which has spin. The bottom grommet will transfer some energy to the top grommet and start it spinning. When this happens the top grommet will appear to jump upward away from the bottom grommet.  

The circular version allows you to do this experiment in a continuous fashion.