Gently pluck the band with a finger. Watch and listen to its vibrations. Now move one pencil to the middle of the book, reducing the distance between the pencils. Pluck the band between the two pencils. When you pluck the whole band, the vibrations are so slow that you can easily see them.
Slower vibrations give a lower sound or pitch.
When you pluck a shorter length of the band, the vibrations are so fast that you can hardly see them. Our vocal cords are like two rubber bands that vibrate in the voice box when a person sings or speaks. The front ends of our vocal cords are attached to it. When we sing, the vibrations of the vocal cords are transferred to our Adam's apples. Guitar strings and the wires in pianos are other examples of how length affects pitch.