A lot of people use Slinkies to introduce kids to waves. But Slinky waves can move too fast for people to really wrap their heads around. Instead, science teacher and filmmaker Alom Shaha suggests, they should try this wave machine. You can build it yourself, and you can do it on the cheap. Here's how.
Shaha demonstrates the DIY Wave Machine for the National STEM Centre, which has thousands of teaching resources like this one available for free through its website. Shaha uses Jelly babies in the video, but Rion Nakaya of The Kid Should See This and physics teacher Frank Noschese recommend Dots for those of us outside the UK.