Standing wave demo. Fill bowl and rub the handles to produce standing waves with spouts at the anti-nodes.
From Arbor Scientific:
The Resonance bowl, also known as the Chinese Spouting Bowl, dates back to the Han Dynasty (202 BC - AD 9) making this an ancient, but still highly effective, way to discuss and demonstrate standing waves.
This seemingly simple bowl takes just the right touch to turn into a fun and engaging demonstration of the behavior of waves and their interactions. Every rub of the handle changes the frequency of the waves in the bowl. With practice, you should be able to produce a standing wave, with spouts of water shooting from the four anti-nodes spaced along the entire rim of the bowl.
The water should spring from the mouths of the four fish engraved at the bottom of the bowl and can be identified by the four streams of water engraved on the sides of the bowl. It is quite the memorable demonstration!