Mexican wave
Sometimes I get an idea in my head and I can't rest until I've worked it through. Tomorrow I'm doing an introduction to waves with my first year classes and wanted to show them how a wave is simply a series of SHMs that are out of phase. What better way to show this than a line of pendula or springs. I don't have enough springs or pendula things so thought I'd give it a go with Interactive Physics.
First I tried with springs but that didn't work so I tried pendula. Setting them off out of phase is the tricky bit, you can't simply let them go at different heights as this will change their amplitude not phase. I hit upon a falling frictionless rod but this fell with acceleration so I had to balance the forces and then give it a downward velocity. Worked quite nicely. All those little balls look like Mexicans, aha a Mexican wave.
Tags: Interactive physics, EE