The singing pipe is a demonstration on sound waves The basis of the experiment is HOT AIR RISES!!! When the molecules within the metal screen tube that is attached to the pipe become heated, the rise within the tube which causes a sound to develop (hence the term " Singing Pipe"). When you cover the top of the tube, it stops the air flow, which also stops the sound. This same method applies when you hold the tube horizontally, the air can no longer flow, and neither can the sound. Whereas, when the tube is positioned vertically, the air can flow and also the sound.
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