What To Do Place the soybeans into the balloon. Grip the balloon near the knotted end and twirl it to get the beans moving inside the balloon. Many forces are acting on the soybeans as they move in the balloon.
Frictional forces slow the movement of the beans.
The force due to gravity slows the bean on its ascent to the top of the balloon, and speeds the bean on its descent to the bottom of the balloon. Centripetal force is supplied by the surface of the balloon pushing the beans toward the center and it keeps the beans moving in a circular motion around the inside of the balloon. The buzzing noise is produced as the beans roll along the inside surface of the balloon, causing the balloon to vibrate. The pitch of the buzzing is determined by the speed of the beans. As the beans move faster, they vibrate more quickly which our ears distinguish as a rise in pitch.