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How Do Sound and Matter Interact?

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

Learn how sound and matter are related and what happens when a sound wave reaches a new material. Also discover how absorption and reflection of sound can be useful. Then, test your knowledge with a quiz.

What is Sound and Matter?

Matter is all around us. And so is sound. It's hard to ever go anywhere that's truly in silence. Despite these things surrounding you every day, do you really know what they are?

Matter is the stuff in the universe: the physical material which takes up space and has mass. So what is mass? Mass is the measure of how much of that stuff you have, and it can be figured out by putting an object on a scale.

Sound is what happens when you transmit vibrations of energy through that matter. Sound is made up of wave vibrations. When you talk aloud, the motion of your vocal cords causes the air to vibrate. Air is made up of molecules, and as those air molecules vibrate, they hit each other. Because of these collisions between air molecules, a sound will spread out from one side of the room to the other very quickly.

Sound waves in the air
Sound waves in the air.

You might find this hard to believe, but that's all sound is: vibrations and collisions of air molecules spreading around a space. When those vibrations reach the inside of your ear, they make your ear drum vibrate, and that allows our brains to detect and make sense of the sound. That's how we hear things!

Sound moves through the air to reach your ear.
Sound moves through the air to reach your ear.

So, sound moves through some matter in the form of vibrations, but one sound wave can also collide and interact with other matter. What happens when one of these vibrations in the air reaches a solid surface? Let's talk about the two possibilities: absorption and reflection.

Absorption of Sound

When a sound vibration reaches a new material: an object, one thing that can happen is that the sound can be absorbed. This is often called sound absorption. Sometimes this is a good thing, and sometimes it's bad. If you're recording a new hit single in a recording studio, this absorption is probably good.

When you sing into a microphone in one of these studios, the walls are usually covered in soft, rubbery shapes. These materials and shapes are designed specially to 'soak up' the sound because people want to record a pure sound with the microphone. They don't want the sound to bounce off the walls first and then go into the microphone, because that will sound muddier and not as nice. Using the concept of sound absorption is one of the ways music artists create such pristine, clear recordings.

Sound absorbers like those used in studios
Sound absorbers like those used in studios

Lower frequencies tend to go through materials more easily without being absorbed, which is why it's so easy to hear when a neighbor is playing music with a heavy beat, or a deep man's voice more than a higher woman's voice.

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