If you really want to dive deep into the physics of sound then I suggest you pick up a textbook or Wikipedia article to find all the information your heat desires. But for the sake of this article, and for those of you who want a simpler and quicker overview, I’ll explain what sound is and how it functions.
In the simplest term, a sound is a wave. And just like a wave in the ocean, a sound wave is a bunch of particles bumping into each other, causing a perceived wave that moves through a medium. The air that we breath is really just a big pool of various gas particles, bumping into each other and swirling around. And when you, for example, clap your hands, the impact of your hands upon each other causes the closest air particles to move outward. As they move outward the particles bump into other particles, which thus bump into even more particles. This chain reaction of bumping creates a wave that spreads outward in all directions from your clapping hands and ultimately bumps into your eardrums. And this bump against your eardrum, my friend, is perceived by your brain as a sound.
Sound waves can travel through any medium that offers moving particles that can bump into each other, such as air and water. Sound doesn’t travel well through hard substances since the particles are tightly packed and resist movement from waves. Beyond the atmosphere in the emptiness of space, it’s a well-known fact that no one will hear you scream since there are no particles present to create a wave.
All materials absorb the energy from sound waves, but some more-so than others. For example, a steel wall will absorb very little energy since its particles are tightly packed, causing the sound wave to deflect away from the surface at nearly the same force it had before impacting the wall. Alternatively, foam will absorb much more energy from a wave since the foam’s particles are looser and more likely to transfer energy from the wave. This results in the wave bouncing off the foam with far less energy. The differences perceived will be a difference in volume—a wave off a steel wall will be louder, while the one off the foam is quieter. You can easily notice these differences in your own home. Make noise in your kitchen and will likely hear your noises bouncing back at you from the hard-counter tops and refrigerator door. Most people will perceive this effect as “my voice sounds farther away” or “the room is nosier.” For the opposite effect, walk into your family room or bedroom where there will likely be carpets, blankets, and pillows to absorb sounds. This room will sound quitter and your voice might sound closer to your mouth. Since all rooms are different and vary at the atomic level, technically all rooms will sound different and unique. No two rooms will sound the same.
Us humans can hear only a small portion of sound waves in the air. Out of the entire audio spectrum, our eardrums can only perceive waves between 20hz and 20,000hz. To put that into perspective, there might be waves all round us at 100,000hz or even higher, but we will never hear them because they are so far above what our ears can pick up. We’ll get more into frequencies and hertz in the article titled “The Sound Wave.” But for now, just understand that 20hz is a very low pitched sound and 20,000hz (abbreviated 20khz) is a very high pitched sound to our ears.
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