Physics trivia

# Physics and music: curiosities

Did you know that physics and music are closer than they seem? The songs are built based on a succession of sounds played periodically.

Music or noise?

The main characteristic that physically differentiates music from noise is its periodicity. The songs are generally harmonic, while the noises do not have any periodicity.

Songs are constructed according to precise scales of musical notes, which are repeated and played sequentially at different frequencies and pitches . These scales are responsible for defining the ratio between the frequencies that are emitted by musical instruments. It is very common to hear songs that use octaves, for example. Octaves are successions of two notes emitted by the same musical instrument, one with twice the frequency of the previous one. The use of octaves produces a pleasant sensation to human ears and is present in many compositions.

In addition to the octaves, it is also common to find, in several compositions, sequences of tones in proportions such as 4:3 or 3:2.

## Natural frequency

All things have a frequency of vibration of their own, characteristic of the bonds formed between their atoms. When we hit a silverware in a glass, the sound we hear refers to the resonance of the atoms that form the glass, arranged in that configuration. At that moment, we can admit that its atoms vibrate in unison.

In the case of strings , such as those used in electric guitars and acoustic guitars, the fundamental frequency is determined by the pull applied to it, as well as its linear density . This explains the fact that the strings present in the instruments have different thicknesses.

## How do instruments make sounds?

The sounds emitted by musical instruments are produced by various mechanisms: by the vibration of strings, membranes or by the passage of compressed air through sound tubes. Despite this, all these oscillations have one thing in common: they are capable of producing harmonics . Harmonics are special sound frequencies that significantly increase the sound intensity emitted by musical instruments.

Did you know that humans have their own set of musical instruments? We are able to emit loud, clear and intense sounds thanks to the vocal cords, which are vibrating cords attached to a long sound tube closed at its base, the larynx . Our powerful musical instrument is also quite versatile, being able to produce a variety of frequencies and amplitudes.

## Shells and the sound of the sea

Have you ever felt like you heard the sound of the sea when you brought a shell to your ear? This is due to the shape of the shell. Its spiral cavity makes the sounds that enter it reverberate. Reverb ensures that you can hear a sound even if it has been out for some time. This phenomenon occurs thanks to the multiple reflections suffered by this sound inside the shells.

Reverberation is critical in theaters and cinemas. In these places, strategically placed reflective surfaces are used to ensure the ideal permanence time of each emitted sound, enabling the emergence of more vibrant sound effects.