Sound is created through vibrations. These vibrations create waves that travel through the air until they reach and are absorbed by your ear. Our brain interprets these
vibrations as different pitches.

Pitch is a measurement of how high or low a note is. It is caused by frequency—how often the sound waves repeat themselves. Frequency and pitch are measured in a unit called hertz; a squeaky, high pitch sound has more hertz than a deep, low pitch sound.

In this experiment, the vibration occurs when you tap on the glass. When there is just air in the glass, they should sound nearly the same. However, when you add water, the vibrations have to go through that water as well, so when the vibrations get to your ear, they sound different!

Try It!

• We suggest using glass, but what about other kinds of cups? How does the sound of plastic or ceramic glasses differ?
• Pick a note and try to match it! Experiment and adjust the water in the glass to match your note.
• Take this to the ultimate level! Pick a simple song and try to recreate it! Adjust the water levels in each glass to match the notes in the song. You may need more cups for this. For example, “Twinkle Twinkle Little Star” would need at least 6 cups!
• Sound is caused by vibrations. If you have any musical instruments in your house, try them out! Can you see or feel any vibration?