10 Connections Between Physics and Music

Neil Diamond: physicist (sort of). © MIKE SEGAR/Reuters/Corbis

Music doesn't emerge from random creative inspiration. Songs aren't chaos. Instead, they involve structure, pattern, repetition and other characteristics that make them recognizable to the human ear. In the end, music is a sort of science -- a fascinating, pulsating type of sound that peers through people's aural perceptions and into the universe beyond.

We humans have organs specifically designed to detect and understand sound. Our fleshy ears snag all sorts of sounds, from the chirping of crickets to the pounding of jackhammers, to classical music streaming through radio signals.

Few of us, however, take the time to really think about how those sounds move from one place to another. And not many of us probably think about why a jackhammer doesn't qualify as music but Neil Diamond does (usually). It's not just a subjective judgment. There's actually science behind music.

All music emerges from the principles found in physics and math. In fact, centuries ago, some academics considered the study of music to be a kind of science. It was regarded as an important discipline alongside mathematics, geometry and astronomy.

These days, most people agree that music is important, but it may not get the scientific respect that it should. Whether you listen to The Bangles or Boards of Canada, maybe music's scientific pedigree deserves a closer look.

Everything else in the universe is connected. So too are music and physics. Keep reading and you'll see how physics and music are interwoven.

10
Wave Your Hands in the Air
These kids probably don’t think of it this way, but as they practice their instruments, they’re learning to control sound waves. ©Tim Pannell/Fuse/Thinkstock

Sound is made of types of waves, including mechanical, longitudinal and pressure waves. Vibrating objects create these waves, which subsequently travel through a medium, such as air or water.

Jiggle a wiggly spring on one end. The vibrations you create move from one end to the other as energy is transferred through each coil. This is a type of mechanical action, as each particle of the spring affects the others. Similarly, as music emerges from a vibrating speaker, it vibrates the air particles nearby, creating a ripple effect that makes the music audible at a distance.

This mechanical action is considered longitudinal because the sound travels in parallel to direction in which the sound wave moves. In other words, a sound wave directed forward causes sounds to travel forward, too. Pretty simple.

Sound waves are made of a series of high and low points. As they move through a medium such as air, the air particles compress and decompress. So sound waves are also pressure waves.

Controlling these different waves, which represent important principles of physics, is how people learn to make music.

9
Hertz So Good
Your ears are naturally able to detect frequency fluctuations. ©moodboard/Thinkstock

Want to make a pretty sound? Learn to control sound wave vibrations.

Sound waves move at a specific frequency. A wave's frequency basically just indicates how rapidly or slowly a medium vibrates as a sound wave passes through it. Scientists use Hertz (Hz) units to refer to frequency; a single vibration per second is 1 Hz.

Ears are constructed to pick up on fluctuations in frequency, because a sound's pressure waves affect the eardrum. Humans often refer various frequencies with the term pitch. A high-frequency sound is higher in pitch; lower-frequency sounds have lower pitch.

Play specific frequencies simultaneously and you'll create lovely sound. That's especially true when a second sound wave has, for example, twice the frequency of the first. We denote this scenario with a frequency ratio of 2:1, which is also called an octave.

With a musical instrument, you can create all sorts of different frequency ratios, such 4:3 or 3:2. Some of them sound especially nice to the human ear, and we put them to use in songs. A lot of music, then, is ultimately a blend of sound waves with whole number ratios between their frequencies.

8
Standing Waves
The waves that carry sound behave very similarly to water waves. ©Fuse/Thinkstock

Music is made up of sound waves. Those waves behave like those found, for example, in a lake.

If you watch as waves roll into a flat-faced dam on a windy day, you'll eventually see a wave carom backwards off of the dam and directly into another incoming wave. The result is a taller, more massive tower of water. Likewise, the lower parts of the wave get even lower.

This is called a standing wave. If you fashion a container in a specific shape, sound waves will travel in a controlled manner, resulting in a predictable, consistent standing wave that makes a tone. The consistent nature of a tone is what separates it from noise.

So horns and string instruments ultimately help the player make a number of different standing waves. Played skillfully, listeners hear a song.

7
Pattern Recognition
If the members of an orchestra all do their own thing, you just get noise. But if they work together to play a piece of music, listeners hear glorious patterns. ©Digital Vision/Photodisc/Thinkstock

If you're on a road trip and flip on the radio, only to hear a steady, one-note tone, you're probably not going to keep listening. That's because a single, unending tone isn't music. There's no pattern.

Noise is just a chaotic jumble of sounds. For example, noise is jackhammers echoing through a corridor of buildings while cars honk their horns randomly.

In music, patterns emerge. If you look at visual representation of music's wave patterns, it's a regular, predictable up and down series of peaks and valleys. A representation of noise, however, has irregular peaks and valleys, so there's no music. All you get is weird, unpredictable sounds that don't generally make a positive impression on the human ear. (Though of course, there's no accounting for taste – some people find discord beautiful.)

6
Amp Up Your Amplitude, Dude
Most rock gods probably don’t credit their performances to physics, but without amplified sound waves, they couldn’t be heard by large crowds. ©Creatas/Thinkstock

Let's assume you enjoy the occasional fiery guitar solo. As such, it's probably safe to assume that when said solo hits its peak, you crank up the volume to get the full effect.

To create a louder (or more intense) sound, it helps to start with a louder vibration. Tapping a drum kit makes soft sounds; pounding on it like a crazed Dave Grohl makes louder sounds. In short, the more work you put into creating the drumming sound, the greater the vibration and the greater the amplitude that moves into the surrounding air particles, radiating outwards toward adoring fans.

Of course, in a large concert hall filled with loud, drunken fans, that drum kit would hardly be audible. So many performers use electronic amplifiers, which take sound waves and increase the intensity and loudness so that they fill a stadium (and likely deafen people standing too close to the speakers).

5
Fearsome Interference
Concert halls are carefully designed to avoid sound wave dead spots. ©gnagnel/iStock/Thinkstock

Sound travels in waves of pressure made up of compressions and rarefactions (the opposite of compression). If you were to stroll about a large room as speakers played music from a stage in the front, you'd encounter areas where the music was louder or softer, as the waves cause interference with each other.

The spots where compressions meet each other are louder. Areas where rarefactions collide are softer.

And where compressions and rarefactions smash together? There's little to no sound at all. When architects design concert halls for musicians, they must carefully consider the acoustics of the building. An improper design results in dead spots where sound waves cancel each other out.

This same principle works in noise-cancelling headphones. These headphones detect incoming sound (like a baby crying on an airplane) and create opposing sound wave, which eliminates the cries and lets you enjoy Mozart instead of, "Mommy!"

In a concert hall, to stop interference and dead spots, engineers often install padded walls or panels that absorb sound waves. These panels reduce echoing and thus the weird interference that would ruin a listener's experience.

4
Natural Frequency
Music of molecules: Atoms are constantly in motion, vibrating, creating the natural frequency of the objects they’re part of. ©Alexander Bedrin/iStock/Thinkstock

All matter is made up of teensy atoms. Those atoms are continuously in motion, meaning that all matter vibrates to some degree. All objects, when struck or strummed, have a natural frequency (or frequencies) that they produce.

Strike a tuning fork and it will produce a single, pure tone because it vibrates at only one natural frequency. Blow air through a saxophone, though, and you'll hear multiple natural frequencies.

A saxophonist changes the sounds coming from the instrument by altering the amount of air being forced through the horn, and also by changing finger positions on the keys. There is a whole number ratio between the keys, and when a practiced person plays, the resulting sounds are wonderful to experience.

Chuck a wine glass onto a concrete floor. You'll hear the natural, high-pitched shattering sound indicating the glass's natural frequency. That's not music, though. That's noise.

3
Resounding Resonance
The air moving inside a cello is what gives it its sound. © arkadiuszkomski/iStock/Thinkstock

The body of a musical instrument, such as a trombone or violin, isn't what makes sound. It's the vibrating column of air inside the instrument that produces what we hear.

However, the shape and size of the instrument determines the sounds it creates. Only the sound waves that fit in the instrument are audible. These are the waves that resonate (get louder) within the instrument. The waves that don't fit are simply lost.

You can visualize this phenomenon by imagining a child on a swing. After you start the swinging process, the swing finds a natural pace, or frequency. Trying to push faster or slower just disrupts the swinging (and makes your kid very frustrated with you).

Tubas resonate at low frequencies. That's why they make deep, low sounds. A piccolo, with its tiny, short enclosure, naturally resonates at high, piercing frequencies. Thus, instrument makers keep the properties of resonance very much in mind as they design each piece.

2
Vibratory Revelation
If you mounted guitar strings on a flat board and strummed them, they would sound very different than they do on the instrument. ©John Howard/Digital Vision/Thinkstock

Suspend a string between two points, pull it tight and then snap it with your finger. You'll hear an audible sound. Take a similar string, mount it to a guitar and then pluck it. Again, you'll hear a sound, but this time it will be much louder.

You're experiencing an aspect of forced vibration. The greater the surface area of an object you strike or strum, the more it makes contact with the surrounding medium, such as air. It's called forced vibration because the air is being forced by the instrument to vibrate at a frequency that's not its own.

Musical instruments leverage forced vibration to make sounds louder than they'd otherwise be. A piano uses a sound board, and a violin has a hollow body attached to the fret board. Both help to increase loudness for listeners.

1
Time and Anticipation
Even if an audience has never heard a piece of music before, listeners can intuit what will happen next, because we instinctively recognize and anticipate patterns. ©eurobanks/Thinkstock

Music's patterns join together time and what would otherwise be just noise. A room full of people playing instruments independently makes nothing but an ear-rending racket. When they play their instruments in time to the same sheet of music, though, the result is amazing. It's music.

Yet it's not only the players who understand these songs. The audience, too, picks up on melodies and learns to anticipate a chorus and refrains. Even if you've never heard a particular song before, you almost instinctively begin to understand a song's structure and pattern and timing.

This speaks to a level of interconnectedness that harkens back to physics. It might not quite be quantum mechanics, but it's yet another intersection – of many – in which music and physics collide.

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Author's Note: 10 Connections Between Physics and Music

Whether we realize it or not, we're all in tune with music and physics. We clap and sing along to songs on the radio. We splash around in bath tubs and learn to control the waves (sometimes making a huge mess in the process). Intuitively, we come to recognize resonance, frequency, standing waves and other abstract terms without even knowing exactly what they mean. Some people, like the Bachs and Mozarts of the world, grasp these concepts more firmly and put them to use with the discipline of true scientists.

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Sources

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