Resonant Rings

Materials
Sheet of cardboard 1 foot long, several inches wide
Large sheet of construction paper (14 x 20 inches)
Masking tape or transparent tape

Cut four or five 1-inch wide strips of construction paper. The longest strip should be about 20 inches long. Each strip should be about 3 inches shorter than the previous one. Form the strips into rings by taping the two ends of each strip together. Tape the rings to the cardboard sheet as shown in the picture.

Shake the cardboard sheet back and forth. Start at very low frequencies and slowly increase the frequency of your shaking. Keep shaking the cardboard faster and faster. The largest ring will begin to vibrate strongly again. Each ring will vibrate at more than one frequency, but the shape of each ring will be different for each resonant frequency. Notice that different rings vibrate strongly, or resonate, at different frequencies.

The biggest ring has the largest mass and the least stiffness, so it has the lowest resonant frequency. Put another way, the largest ring takes more time than the smaller rings to respond to an accelerating force.

For more details on this snack, go to 
http://www.exploratorium.edu/snacks/resonant_rings.html