Water glass xylophone: the music experiment

How to make a water glass xylophone

You need five glasses that are all the same (drinking glasses, mason jars or glass bottles all ring when tapped; thin glass changes more than a thick jar), or five identical plastic bottles for blowing (500 ml, the 16.9 oz water bottle, smooth neck), a jug or pitcher of water, a wooden spoon or a pencil, and a towel. Food colouring is optional: it makes the water levels easy to see and doesn't change the notes.

Line the glasses up and tap each empty one first: identical glasses ring almost the same, and one that is clearly higher or lower goes back in the cupboard. Choose Tap above and fill glass 1 almost to the top, leaving a finger's width. Press the button and tap the rim once, gently, with the spoon. That note is your first one, whatever it is. For glass 2 to 5 pour a little less water each time; after every tap Mika says a little more water or pour some off. Pour in sips, then tap again. With plastic bottles choose Blow: bottle 1 half full, blow softly across the top like a flute, and each next bottle gets a little more water. When all five are right, Mika plays the scale and shows Mary Had a Little Lamb by numbers.

How does a water xylophone work? The experiment explained

Tapped glass: more water, lower note. The spoon makes the wall of the glass ring, bending in and out hundreds of times a second. Pitch is how high or low a note sounds. It is set by how many times a second the wall swings, its frequency, counted in hertz (Hz). The swinging wall pushes the air, and those pressure waves, sound waves, carry the note to your ears. The water clings to the wall and has to move with it, so the wall is heavier and rings more slowly, and slower means lower. It isn't the water that sings, as many pages say: an empty glass rings too, only higher. The water near the rim counts most. A half-full glass sounds only a little lower than an empty one; most of the change happens in the top half (A. P. French worked this out for wine glasses in the American Journal of Physics, 1983).

Blown bottle: more water, higher note. Blowing across the neck makes the air inside the bottle sound, the way a flute does. Water takes up space, so less air is left, and a smaller pocket of air sounds higher. Halve the air and the note goes up about six semitones, half an octave.

So which glass has the highest pitch? Tapped, the emptiest one. Blown, the fullest one. A glass bottle can do both: tap it and blow it with the same water inside, and as you pour the two notes move in opposite directions. Children can hear it happen: as the water goes up, the tap goes down and the hoot goes up.

Water xylophone songs by number

The numbers are the glasses, 1 the first and 5 the last. All of these fit on five.
Hot Cross Buns (three glasses, the easiest): 3 2 1 · 3 2 1 · 1 1 1 1 · 2 2 2 2 · 3 2 1
Mary Had a Little Lamb: 3 2 1 2 3 3 3 · 2 2 2 · 3 5 5 · 3 2 1 2 3 3 3 · 3 2 2 3 2 1
Ode to Joy: 3 3 4 5 5 4 3 2 · 1 1 2 3 3 2 2 · 3 3 4 5 5 4 3 2 · 1 1 2 3 2 1 1
Jingle Bells (the chorus): 3 3 3 · 3 3 3 · 3 5 1 2 3 · 4 4 4 4 · 4 3 3 3 3 · 3 2 2 3 · 2 5 · 3 3 3 · 3 3 3 · 3 5 1 2 3 · 4 4 4 4 · 4 3 3 3 3 · 5 5 4 2 · 1

Twinkle Twinkle Little Star needs a sixth glass, one step above 5 (blown: a little more water; tapped: a little less): 1 1 5 5 6 6 5 · 4 4 3 3 2 2 1. Happy Birthday needs eight glasses, a full scale: sol la ti below your five, so number them again, the new low three as 1 to 3 and the tool's five as 4 to 8: 1 1 2 1 4 3 · 1 1 2 1 5 4 · 1 1 8 6 4 3 2 · 7 7 6 4 5 4. The low three need more water than the tool's first glass when tapped, so for this song start that glass about half full; blown, they need less. The tool tunes five; tune the extra glasses by ear, singing up the scale until each next glass sounds like the next step (for Twinkle's glass 6, until little sounds right).

Stick a number on each glass before you start. Play slowly, one tap per syllable, and let each note ring before the next. In a group of five, each child holds a beater and plays only their own number, so the song passes along the row.

What is Brumm Kids? · Privacy at Brumm Kids

Water levels for each note

No water chart works for every glass: the note depends on the glass's shape and how thick its wall is, which is why the tool listens instead. One rule does hold for tapped glasses: equal steps of water do not give equal steps of note. The usual recipe of a quarter cup less in each glass puts the full glasses far apart and makes the nearly empty ones sound almost the same. Keep all five glasses in the top half and make the steps smaller towards the top. Thin glasses stretch further than thick tumblers; if a heavy glass won't reach five notes, swap it for a thinner one.

Blown bottles follow the air, so a rough start can be worked out. For five 500 ml bottles, with bottle 1 half full:

The neck holds air too and bottles differ, so take these as a start and let Mika do the last sips. Mi to fa is a half step: bottles 3 and 4 differ by one sip. The tool names the notes as letters (C D E F G A B), and the scale starts on whatever glass 1 rings. To start on C, change the water in glass 1 and press Start again until it reads C.

Things to try next

• Tap high or low, soft or hard. The note stays the same: each glass has one ring. Near the rim the wall swings most, so it rings loud and clear; low down near the base it hardly moves and you get a quiet, dull knock. Tapping harder makes the note louder, not higher. A hard knock adds clinks on top, can confuse Mika and can crack a thin glass.
• Change the beater. Wood gives a soft note, a plastic spoon a click. A metal spoon gives a bright clink with extra high rings on top: try it only on a sturdy glass or jar, gently, with a grown-up.
• Other drinks. Milk or juice instead of water: almost no difference, they weigh about the same as water. Cooking oil is a little lighter (about 0.9 g per ml), so at the same level a tapped glass sounds a touch higher. A blown bottle doesn't care what is inside, only how much air is left.
• Rub instead of tap. A wet finger circled slowly round the rim of a thin wine glass makes it sing the same note it rings when tapped. Grown-ups can tune a set with the wine glass tuner.
• Hear it in a beat. The button under the scale takes the five notes into Brumm Kids, where a marimba plays them over a beat and the children can sing along.

For parents and teachers

For preschool and the first school years. From about four, children can pour, listen and say higher or lower; blowing across a bottle takes practice, and many younger children can't get a hoot yet, so a grown-up blows and the child pours. Glasses only with a grown-up at the table, tapped gently with wood, never a metal spoon on a thin glass. A few blows in a row can make anyone dizzy: one blow, then a breath.

In a group of five, each child looks after one glass or blows their own bottle. Before the water goes in, everyone guesses: will the note go up or down? Then one child pours, one taps, and the group listens. Good questions: what is ringing, the glass, the water or the air? Do two glasses with the same water sound the same? Does it matter where you tap? Nobody is scored or compared. For the youngest, two glasses are enough: one nearly full, one nearly empty, which is higher? (Higher or lower is the same question as a game.)

No worksheet needed. Each child draws their glass, marks the water line and writes the letter Mika shows (C, D, E …). Lay the drawings in a row and the class sees the steps: tapped, the lines step down; blown, they step up. Change one glass at a time, so everyone knows what made the note move.

What is a glass xylophone called?

Strictly, a xylophone is wood: xylon is Greek for wood. Bars of metal make a metallophone, like the glockenspiel, and instruments of glass are sometimes called crystallophones. Glasses tuned with water have their own names. Musical glasses were a concert act in 18th-century Europe: the composer Christoph Willibald Gluck played a concerto on 26 drinking glasses in London in 1746. A glass harp is a set of stemmed wine glasses fixed upright to a board, each tuned by its water or ground to pitch, played by circling wet fingertips round the rims; a player can rub several at once and get chords. In 1761 Benjamin Franklin built the glass armonica, which does the same with nested glass bowls on a rod turned by a foot treadle, and Mozart wrote for it in 1791. In India the jal tarang is a row of porcelain bowls tuned with water and struck with two thin sticks, heard in classical music to this day.