Wave

I have started teaching A' Level physics twice a week to a girl at an evening school in Houshayu. I did A' Level physics myself and use all the mechanics aspects regularly in my engineering job but I am a bit rusty in some areas, especially the electronics bits. However, the school seem happy with me and the girl seems to be learning a lot so I must be doing something right! I bought this slinky to help me explain waves. Here you can see a standing wave as the spring vibrates at the second harmonic frequency.