The Resonance Bowl can be traced back to ancient Tao tradition in China during the Han Dynasty (202 BC – AD 9) making this an ancient, but still highly effective, way to discuss and demonstrate behavior of waves and their interactions. Fill the bowl with water, rub the handles just the right way, and water will shoot up like tiny fountain jets. Some resonance bowl masters claim to even get water leaping as high as 2 feet!
The Concepts Behind the Resonance Bowl
The vibration of the handles, in turn, increases the vibrations of the bowl, causing the bowl to vibrate. In Physics, we call this Resonance, where one vibrational frequency causes the natural vibrational frequency of another object to increase. The vibration causes two phenomenons to occur:
a. The bowl will create a sound, depending on its size (~196 Hz for a "big" bowl and ~330 Hz for a "medium-sized" bowl).
b. In addition, standing waves are created in the water illustrating an interference pattern called a Chladni pattern. Standing waves are produced by the addition of two identical waves traveling simultaneously in opposite directions through any elastic medium. These waves will constructively and destructively interfere with each other as they pass one another. The resulting composite wave from the addition of these two waves will form a standing wave in the metal rim. The standing wave that is produced sets up FOUR areas of maximum vibration called antinodes, these are areas in the water that "spout" and cause the water droplets to jump off the surface. There are also FOUR areas where minimum vibration occurs and these are known as nodes. These nodes show very little water rippling while the antinodes show maximum water rippling. With practice, you should be able to create four antinodes along the entire rim of the bowl that are so strong that the water will spray out of the bowl. This occurs where the artist intentionally engraved the four fish mouths.
- If the bowl is touched firmly at any of the antinodal positions, the finger will absorb the vibrational energy, and the waves will be reduced or totally stopped. This effect is called dampening. However, if the bowl rim is touched at any nodal area, there will be little energy lost since the node has minimal vibrational energy and the spouting should continue as before.
- By varying the amount of water in the bowl, you can investigate with your student what might be the optimal water level for maximum effect and have them explain why. Is it easier or more difficult to create the standing waves with different water levels?
- By rubbing harder and faster, you can cause the bowl to produce a high-pitched squeak. When it does, you can sometimes create additional nodal and antinodal points in the water.
- Try floating a cork in the water while playing with the Resonance Bowl. Observe its movements.
- You can also place a small amount of sand in the bottom of the bowl (…instead of water) and observe how the vibrations move the sand.
Thank you to Buzz Putnam of Whitesboro High School in Marcy, NY for his contributions to this article.