Stationary wave on a distraction toy

 

I was given this piece of elastic at a meeting as one of those fidget toys to occupy my hands. I spent the meeting making stationary waves. At the right frequency, the outgoing wave interferes constructively with the reflected wave making a pattern when the maximum point or anti-node stays in the same place. The fundamental was easy. The first overtone or second harmonic, with two loops, was possible but much harder and very unpredictable.