Sound is the vibration of the air, and vibrating objects can make sound. When you rub the cloth on the the string, you make the string vibrate. Many musical instruments use the vibration of strings to make sound. The cup amplifies the sound (makes it louder). The hollow part of many instruments, like guitars, amplifies the sound much as the cup does.
Cuicas are Brazilian friction drums often used in samba music. They are normally made from metal or gourds with an animal skin head. A thin bamboo stick is attached to the center of the head, pointing into the center. The pitch can be changed by varying the pressure on the head.
Mess Kits are single-serving experiments that allow kids to explore scientific concepts at their own pace. Visitors are encouraged to complete as many as they want! See all Mess Kits.