MrG
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- Noise Tube
They're stilla vailable in science centres. There's a little thing inside that emits the "groan" as it falls and air passes through it. It's brilliant for showing everything accelerates at the same rate under gravity: tip it up and let the bit inside begin to fall. Then drop the whole thing and the groaning stops because both it and the outer tube are falling. Then catch the tube and the groaning starts again.