simple science experiments

when my daughter suddenly asked me while holding two glasses of water (different amounts in each) and a spoon 'when i hit each glass with the spoon why does it sound different?' i had a light bulb go off in my head and took this opportunity to do a little experiment.

we got six identical glasses, filled each one with different amounts of water. with spoons we tested the sound coming from each glass, we discussed why the glass which was full of water had a low sound and why the got higher as the water amount got lower, we even pretended to be molecules of water and acted out what would happen inside the glass with more water (the vibrations will be slower) compared to the glass with less water.