If your orchestra students are familiar with harmonics, you can continue the earlier jump rope demonstration posted on the Orchestra Network.
Have two students hold opposite ends of a jump rope and ask them to shake the rope. Challenge them to find a way to make the rope vibrate so the point in the center remains still. This will take some trial and error, but when they figure it out, the rope will be split into two sections with the center appearing to be pinched. The technical term for this seemingly pinched point is a node.
How does this relate to stringed instruments?
Harmonics split a string into simple fractions, the most basic of which is ½. The pitch sounded by a harmonic halfway up the string is an octave above said string. Other fractions of a string’s length will produce even higher harmonics.
Students can produce the entire range of possible harmonics by lightly touching a string and moving a finger closer and closer to the bridge while bowing continuously. At each point where a harmonic is sounded, a string player’s finger is forcing the string into pieces.
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—Gregory Reinfeld, February 2, 2012. © National Association for Music Education