Experimental materials and utensils: hangers, thin wires, rubber bands
Experimental steps:
1. Tie a dozen thin wires on the hangers, spaced approximately 5 mm, tie a popcorn to the other end of each wire and hang the hanger.
2. Find a rubber band with good elasticity, bite one end with your mouth, tighten the other end with your left hand, close to the lower part of the popcorn, and use your right finger to stir the rubber band. Since the middle part of the rubber band vibrates the most, some of the popcorn in the middle rises first. The more the rubber band vibrates, the more popcorn swings; when the rubber band stops vibrating, the popcorn stops swinging.
As the rubber band vibrates, it causes the surrounding air to vibrate, causing the popcorn to swing. This experiment can also be used to illustrate how sound propagates. If the frequency of this vibration is 20 to 20,000 Hz, and it reaches the eardrum of the human ear, the sound can be heard.