Why Do the Glasses Make Different Notes?

When you tap a glass gently with a spoon, the glass begins to vibrate.

Those vibrations make the air around the glass vibrate too. The vibrations travel through the air as sound waves until they reach your ears.

But something interesting happened in your investigation.

The glasses didn't all make the same sound.

What Does the Water Change?

Adding water changes the way the glass vibrates when you tap it.

A glass containing more water tends to vibrate more slowly and produces a lower-pitched note.

A glass containing less water can vibrate more quickly and produces a higher-pitched note.

That's why changing only the amount of water allowed you to create a whole range of notes.

What Is Pitch?

Pitch describes how high or low a sound seems.

Fast vibrations produce a higher pitch.

Slower vibrations produce a lower pitch.

Scientists describe how quickly something vibrates using a measurement called frequency.

So when you changed the water level, you weren't just changing what was inside the glass — you were changing the sound it could produce.

You Built an Instrument!

By carefully changing the amount of water in each glass, you created different pitches.

Put enough different pitches together and your row of glasses becomes a simple musical instrument.

This same big idea appears in real instruments too: musicians need different parts of an instrument to vibrate at different speeds to create different notes.

Your Rainbow Xylophone lets you see, hear and investigate that idea for yourself.

What About the Food Colouring?

Here's one thing that didn't change the pitch.

The food colouring simply makes the different water levels easier to see and turns your instrument into a rainbow.

The science is happening because of the glass, water and vibrations.

Scientists Say...

Sound begins with vibrations.

Change how something vibrates and you can change the sound it makes.

That is the key discovery behind your Rainbow Xylophone.