This year in Math Quest camp, I decided to teach the kids how to make a xylophone with glasses of water, mixing music and math. It was even more awesome (and easier) than I’d expected!

I loved how this activity mixed music, math, science and technology, and was fun and challenging for kids of all ages. You don’t need fancy equipment or lots of prep; it’s the perfect at-home activity for hands-on, artful math!

**You will need:**

- 5-8 same-size drinking glasses that can hold at least a cup and a half of water each
- measuring cups
- a small wooden or plastic spoon
- food coloring

*I bought 8 glasses at a dollar store to make an octave, but the higher pitches didn’t sound very good on my cheapy (too small?) glasses, so I ended up only using five of them.*

## How To Make A Xylophone With Water Glasses

**1. Set the Stage**

Give kids a glass and a wooden spoon. Ask, “Can you make music with your glass? How can you make different sounds? Do you think the sound will change if I pour water into your glass? (Try it.) If I add more water to your glass, do you think the pitch will get higher or lower?”

Experiment a little with pouring water into the glasses to make different sounds.

**2. Measure the Water**

Fractions and careful measurement are the secret ingredient to making your water glasses sound truly musical. Have kids write down the following musical recipe for how to make a xylophone:

**GLASS 1**: one and a half cups water**GLASS 2**: one and one fourth cups water**GLASS 3**: one cup water**GLASS 4**: 7/8 cup water**GLASS 5**: 5/8 cup water**GLASS 6**: 3/8 cup water***GLASS 7**: 1/8 cup water***GLASS 8**: no water*

*I didn’t use glasses 6, 7, or 8 because the sound started going wonky at those high pitches. If your glasses are higher quality than mine, or maybe just larger, you might be able to make a full octave.*

**3. Tune Your Glasses**

Have kids put the glasses in order from most water to least, not touching each other. Tap the sides or the rims of the glasses one at a time in order to play a scale.

If one of the glasses sounds “off”, you can either re-measure or adjust the water. (If pitch is too high–add water. Too low–pour a little water out.)

If you have a piano, you can match each tone to a piano note. (Or you can use a free piano keyboard app like this one.) This will tell you if your glasses are more or less in tune–and let you know which scale you are playing in!

**4. Add Food Coloring**

Ask kids what colors they want, then have them add 2-3 drops of food coloring to each glass. They’ll do a bit of color mixing here, which is fun.

The colors really do seem to bring this activity to life, and they also help kids differentiate the glasses when kids are playing songs.

**5. Play Music!**

“Mary Had A Little Lamb” is a nice, simple song to start with, especially if you only have 5 glasses.

Hold the spoon lightly from the end so the vibrations ring. This gives it a better sound.

Some of my kids had trouble playing a whole song by ear. I tapped out the song slowly while they drew colored circles in their notebooks to match the notes I played.

Now they can follow the colors and play the song on their own.

## Cool Math Connections

There is a ton of math to be found in this simple activity:

**Measuring liquids**: Kids have to be really accurate in their measurement, otherwise it won’t sound right. Make sure they fill all the way to the top line, and if they use non-liquid measuring cups, to scrape across the top with a butter knife.**Reading and writing fractions**: Read the fractions out loud for the xylophone “recipe” and have kids write them down. Then have kids read you the fractions one at a time when it’s time to measure them out.

**Comparing fractions**: Print out fraction strips, and have kids make each fraction with the strips before measuring. Ask questions like, “Which is more: 1/8 or 1/4? How do you know?”**Equivalent fractions**: How can you measure 7/8 if you don’t have a 1/8th cup? One of my older kids figured out we could measure 1/2, then 1/4, and finally half of the 1/4 cup (1/8). It worked! (Fraction strips make even a challenging task like this one a LOT easier, even for young kids.)**Adding and subtracting fractions:**How much water did we use altogether? What’s the difference between the fractions from one glass to the next?

## Music Notes

- A musical scale goes up by a predictable pattern of notes and half notes: whole, whole, half, whole, whole, whole, half. The difference between the fractions will sometimes be 1/4 and sometimes 1/8–depending on whether it goes up by a whole or half note.
- Music, and sound, are made by vibrations. The faster the vibrations, the higher the pitch. Water slows down the vibrations, so adding more water to a glass brings the pitch down.

The kids loved this activity so much, and it was surprisingly easy to do!

Our “how to make a xylophone” activity opened the way for a bunch more music/math explorations, like determining how many wing beats a second a bumblebee makes by the pitch of a bee’s buzzing, a second homemade xylophone activity using wrenches, and finding the Hertz of various pitches using this app.

What are your thoughts about math music and the water glasses xylophone? Share a comment below!

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