Sound Tubes are our absolute a great hands on sound experiment. When spun in a circular motion, these tubes produce a tone. When swinging it around it creates low pressure at the free end and the higher pressure on the hand end. When whirled in a circle it becomes a simple centrifugal pump. This pressure gradient causes air to flow through the tube. When the air is going through the tube in bounces over the ridges in the tube. Which disrupt the airflow to produce loud, musical tones. The faster the tube is whirled, the higher the pitch of those tones.