Tsunami in a bathtub
Today my first years did the resonance in a bucket experiment. As usual they couldn't believe that the speed of the wave didn't depend on when they pushed the side of the container. One group wanted to get rid of the human input and replace the pushing hand with elastic bands on either side of the container. I explained that it would be difficult to get the frequency of the containers motion to match the wave and suggested they try a vibration generator. As you can see it worked quite well showing that this is clearly an example of resonance. Reminds me of when I used to slide up and down the bath getting the water to swish over the edge. Not a good idea in English bathrooms with carpet on the floor. To perform the whole experiment take the plug out of the bath and observe the change in frequency as the water drains out, leaving you lying in an empty bath making rude noises with your back. Oh, so no one else has done that then... 