(3D40.30) Singing Rods
Stroking the rod with sticky fingers creates longitudinal vibrations in the rod. Longitudinal vibrations are waves that travel along the length of the rod. The waves travel to the end of the rod in which they transmit vibrations to the surrounding air molecules. Longitudinal vibrations of air molecules are then interpreted by your ears as sound. However, that is only part of the story. Some of the vibrations traveling toward the end of the aluminum rod are reflected. The reflected waves return and head back in the opposite direction toward your fingers. On their way back, they collide in a head on collision with similar waves created by your sticky fingers!