1) Ask two volunteers to stretch a Slinky out on the floor or a table to about three to four yards length, with one volunteer firmly holding each end. Have one volunteer give their end of the Slinky a quick push toward the other end, returning the slinky to its original position immediately afterwards. What happens? Do the two ends of the Slinky move towards each other? (No.) What is moving from one end of the Slinky to the other? (A pulse or wave of energy.)
2) Tell students that what they are doing with the Slinky is modeling the way energy in the form of a sound wave travels through solids, liquids or gases. Explain that those substances, known as mediums, are composed of molecules, more or less regularly spaced from each other, like the coils of the Slinky. When one of these molecules begins to vibrate as the result of a sound source’s energy, it pushes against the molecules next to it (a process called compression) before returning to its original position (a process called rarefaction); the process is repeated with the adjacent molecules and so on as the sound wave passes through the molecular structure of the medium.
3) Tell the class they will now be looking at the first of several clips about sound from the PBS program THE MUSIC INSTINCT. Provide a FOCUS for media interaction by asking students how the physical nature of a musical note on a cello differs from that of a handclap. PLAY Clip 1: “The Nature of Vibration.”
4) Review the focus question: how does the physical nature of a musical note on a cello differ from that of a handclap? (A sustained musical note repeats in a regular, cyclical pattern of pressure waves. A handclap is more sudden and chaotic.) Ask students how a cello note and a handclap could be simulated with the Slinky, and have the volunteers perform the simulations as suggested. (A cello note could be simulated by pulsating one end of the Slinky back and forth in a rhythm; a handclap can be simulated by a single powerful push or spasm.)