DL-Simple Harmonic Motion
Demo - Mass on a spring. I put a flat piece of cardboard on the bottom, and hang a 1 kg mass on one of the springs. I put a Vernier Rangefinder under it, and show the graphs of position, velocity, and acceleration. You can make the graphs start so that the position graph is a Sine graph, and show that the velocity is Cosine, and the acceleration is negative Sine.
You can make the position look like a Cosine, and then the velocity is negative sine, and the acceleration is negative cosine.
Demo - Resonance - The classic resonance boxes - I like to de-tune one so it doesn't work, and then tune the other one to match, and then they work again. Radio broadcast uses this principle - the LC circuit in a radio resonates to the carrier frequency.
Demo - Wiggler on a Post - I attach a motor with an off center cam (A vibrator) to a variable power supply and show the resonant frequency - how the amplitude goes crazy. I then show the coupling phenomenon - how it wants to stay in resonance. I talk about washboard roads. You can either go slower than the resonant frequency, or faster - you can show the amplitude curve.
Demo - The Bay of Fundy - Water in a cup - slosh it back and forth at different tempos. You will know when you hit the resonant frequency
Demo - Singing to a Guitar/Banjo/Piano - Sing into the instrument at the same pitch as the string is tuned to. The instrument magically resonates and plays the note. I point out that this is how an orchestra tunes, and it doesn't have to be the same note, it can be a consonant interval like a fifth, and it still works.
Demo - Wine Glass - I put a bit of water in a wine glass and make it sing by rubbing my finger on it. Bowing a string is a similar concept.
Demo - stuff
Lab - stuff