The students already know that vibration causes sound and it has been discovered by playing the classroom percussion and plucking strings on a dulcimer, etc. They also feel their throats when they talk and are silent to feel the vibration and lack of vibration. Okay, that's the background.
Now to get them to discover the other characteristics of sound, each gets a boomwhacker and they're told to hit the boomwhacker on themselves and other nonbreakable things around the room and see what they can find out about sound (without any other hints from me). After a little while, they exchange a long boomwhacker for a short one and continue making sounds.
After a couple of minutes, they sit and I ask them what they have found out about sound. They easily discover that sound has volume and pitch. There's always at least one who discovers timbre from striking different objects around the room.
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