Resonant Rings

“Resonant Rings” consists of circular steel bands of various diameters that are mounted on a plate that has been attached to a loudspeaker. By adjusting the frequency of the sound, a graphic illustration of harmonic resonance can be seen in the rings as they vibrate at various frequencies and in different modes. The frequency of the speaker can be read directly on a digital counter. Exciter levers are provided for two of the rings so they may be struck lightly and their “natural frequency” observed, or their motions dampened.

The frequencies at which each ring vibrates most easily (its resonant frequencies) are determined by several factors, including the ring’s inertia (mass) and stiffness. Stiffer objects have higher resonant frequencies; more massive ones have lower.

Most materials have a natural vibration frequency. When similar frequencies occur in materials that are near each other they are able to pass along or “share” the vibrations. This creates harmonic resonance. If one material is vibrating and the natural frequency of a nearby material is similar, it will begin to vibrate also. This has resulted in disasters when bridges begin vibrating due to earthquake activity. The earthquake waves are passed through the ground supporting the bridge and along the bridge material. This allows the materials to keep repeating the wave (resonating). The specific combination of resonating waves is amplified and will destroy a bridge. For a real-life example, look up the Tacoma Narrows Bridge disaster.

Questions to Ask

Why do only certain rings vibrate at the same time?

Do the rings have to be touched for each to begin vibrating? (Can other rings vibrate without being touched?)

How does the sound cause the rings to vibrate?

Relevant Arkansas Science Frameworks

(PS.5.1.1) PS.6.3.1. PS.6.3.2, PS.7.6.1, PS.7.6.3, PS.7.8.4, PS.7.8.5, PS.7.8.6, PS.7.8.7

"Mini-Vibe" — An activity to do at home or in the classroom