One of the most fundamental ways in which we interact with our surroundings and get to know the world around us is by making use of sounds. Sounds are essential in helping us communicate in the most effective way possible. Sounds play just as important a role in helping us interpret our atmosphere as do sight, smell, or touch. Hearing is one of the most crucial factors that have determined the survival of our species.
The first sound a person hears happens to be in the womb. After spending about 16 weeks inside the belly, our freshly developed ears are able to decrypt music of the womb – the to and fro whooshing of air within the lungs and the movements of fluids in the stomach.
Being so uniquely interlinked with the world of sound around us has, naturally, made us curious to know more about its working. What is sound? Why is it that it decreases the further away we get from its source? Why can’t sound travel through things like glass, the way light can? And, why do voices heard under the water sound so weird?
When we approach the physics of our world, we find that everything is made up of some small fundamental stuff. The electricity that is found in our houses and cities is made up of negatively and positively charged particles. The flow of these charges is what we call current. The light that is found everywhere around us and allows us to see is made up of massless particles called photons. Water waves are made up of water particles carried by air. Hence, sound waves must also be made up of something our eyes can’t see.
To understand this concept, we need to acknowledge the fact that the air around us is not empty, even though it looks clear. Anywhere on the Earth, we are surrounded by billions and billions of stuff that we can’t see. This stuff exists in the form of gas particles. For example, there is oxygen that helps us breathe and keeps us functioning, and there’s carbon dioxide that is ingested by plants all over the world to help them survive. We are submerged in a vast ocean of air filled with countless tiny particles.
The production of sound involves the simple process of vibration, only on a very large scale. If we take a slinky and stretch it horizontally from one end and let it loose, that end will be set into vibration. Soon enough, however, other parts of the slinky will start to vibrate as well, and a full wave will pass throughout the slinky. This happens because the part of the slinky that we stretched was attached to other parts, meaning that each consecutive part forced the other to move to and fro with it.
Essentially, this is what happens when sound is produced from a source. All the particles present in the air are attached to each other by natural forces. One cannot vibrate without disturbing the other. Take a guitar string, for instance. When plucked, it vibrates and, by doing so, forces the adjacent air particles to vibrate as well. These particles move to and fro and collide with the particles present nearest to them, which, in turn, force more particles to vibrate. And so on. The longer and further this goes on, the weaker the energy of the particles becomes, and they produce smaller vibrations. At some distance, the energy of the particles dies, and the sound cannot be heard.
The way we humans produce sounds with our mouths is by using vocal cords, which are present in our throat. When air from our lungs passes through these cords, it causes them to vibrate in different ways, which makes us produce different types of sounds. Similarly, we are able to hear sound when it falls on the part of our ears called the eardrums, and causes them to vibrate.
An interesting way to understand how sound travels is to imagine yourself trying to speak in outer space, outside the surface of the Earth. It is not possible to produce any sounds in space because space does not have any particles in it that can transmit sound, showing that sound always needs a medium to travel from one place to another.