Pluck a guitar string and watch closely. For a moment it blurs, because it's moving back and forth dozens or even hundreds of times a second. That shaking, called vibration, is where every sound begins.
A vibrating object pushes on the air around it and sends out waves of squeezed and stretched air. When those waves reach your ears, your brain hears sound. Musical instruments are simply clever ways to make vibrations and to control them.
High notes and low notes
How high or low a note sounds depends on how fast something vibrates. Fast vibrations make high notes, and slow vibrations make low ones. A handy set of rules works for almost every instrument:
- Shorter sounds higher: a short string or a short tube gives a higher note.
- Tighter sounds higher: tightening a string or a drumhead raises the pitch.
- Thinner sounds higher: thin strings sound higher than thick ones.
- Bigger usually sounds lower: that's why a double bass sounds deeper than a violin, and a tuba deeper than a trumpet.
Strings: plucked, bowed and struck
Most guitars have six strings, but some have seven, eight, or even twelve.
On a guitar, each string is tuned to a different note. When you press a string down behind a fret, you shorten the part that can vibrate, so the note goes up. An acoustic guitar's hollow wooden body vibrates along with the strings and makes the sound much louder.
Many violin bows are strung with real horsehair.
A violin works a little differently. The bow's hair is rubbed with rosin, a sticky tree resin. As the bow moves, it grabs the string, lets it slip, and grabs it again, over and over, so the string keeps vibrating for as long as the bow keeps moving.
The piano is the surprise member of this family. Each key moves a small felt-covered hammer that strikes the strings inside, so a piano is a string instrument and a percussion instrument at the same time.
Wind instruments: a column of air
In wind instruments, the thing that vibrates is the air inside a tube. Something has to set it moving, and each instrument has its own trick.
A trumpet has just three valves, but players make many notes by changing their lips.
On a trumpet, the player's lips do the work. They buzz against the mouthpiece, and the air in the tube vibrates with them. Pressing a valve sends the air through an extra loop of tubing, which makes the tube longer and the note lower. By changing how they buzz, players get many different notes from the same valves.
The saxophone uses a thin reed that vibrates against the mouthpiece, which is why it counts as a woodwind even though it's made of metal. A flute has no reed at all: the player blows across the edge of a hole, splitting the stream of air so that it flutters.
Drums: a skin that ripples
Drums are among the oldest instruments and have been played for thousands of years.
A drum's vibrating part is its head, a thin skin or plastic sheet stretched tight over a frame. Hit it, and it ripples like a trampoline. A tighter head gives a higher sound, and a bigger drum gives a deeper boom. Orchestra timpani even have pedals that tighten or loosen the head, so they can play real notes.
Other percussion instruments, like cymbals, bells and xylophones, don't need a skin at all. The whole object vibrates.
Want to hear the rules in action? Line up a few glass bottles with different amounts of water. Blow across the tops and the bottle with the most water sounds highest, because its air column is shortest. Now tap them gently with a spoon: the fullest bottle sounds lowest, because this time the glass and water are vibrating, and more water slows them down.
In Spinbo, instruments live in the Big Stage world, where little music notes float up behind the wheel. Spin to land on a guitar, a piano, a banjo or an accordion, and hear its name and one clear fact read aloud in your language and in a second one.
Then grab a bottle, blow across the top, and you're making music with physics.
