Sound

Music: how much Physics is there in music? Let’s take this five piece band for instance: the lead singer, the guitar player, the keyboard player, the drummer and the saxophonist. We also have the electrical devices such as microphones, amplifiers and speakers. All these put together has a lot of Physics going on even though when we’re listening to the band playing, equations and physical laws are (for most of us) the last thing on our minds. Where shall we start then? Let’s take the lead singer. How come I can hear what he’s singing on stage even though I’m right at the back of the audience? To understand this, we have to understand what sound is.

If we hear somebody talk, then what this means is that there is this thing called sound which emanates from that person’s mouth and reaches us in our ears. Our brain then interprets this sound as speech. But how does this sound get to our ears? And how is it produced in the first place? Anyone who’s placed his or her hand on the throat while talking would have felt a slight vibration. Sometimes on certain large speakers we can see the front panel moving back and forth in time with the loud music pumping out of these speakers. The cinema is another place where we can experience the vibration caused by sound. These are physical indications or evidence that vibration and sound are connected in some way. In fact sound IS vibration. A sound is produced when something vibrates. We might not necessarily be able to hear it – either because it’s not loud enough or it’s a sound which our ears cannot register. There something called frequency or pitch that has to do with what range of sounds we can hear but we’re not going to talk about this right now. Back to our vibrations. So, vibrations produce sound. What is it that vibrates that makes the sound? In the case of our voice, we have small strings in our throat called vocal chords. Somewhat like a guitar string which when plucked makes a sound. This vibration of the vocal chords is what makes us speak. The sound coming from the vocal chords is also amplified inside the mouth. With our tongue, palate and lips we further change this sound to articulate different words. But it all starts with the vibrating chords.

Now once the vibrations are produced, they move from the source of the vibration and travel through something. This something is called the medium. We’ve found out, through experiment, that without a medium, sound cannot travel. That is, sound cannot propagate in a vacuum. This is the principle of which double-glazed glass windows are based. By encapsulating a layer of vacuum between two glass sheets, one can reduce the amount of outside noise from making it into the room.

The medium is necessary for sound to travel from one place to another. Air is a medium made of gas. But this doesn’t mean that sound cannot travel through other kinds of medium. Actually, sound can travel through anything as long as that thing vibrates. Sound travels through wood: if you place your ear on one side of the table while tapping on the other side, you can feel then sound moving through the table. Native Americans, apparently, placed their ear on the railway track and could tell whether a train was approaching from a distance or not, way before they could actually see any train. The sound the train wheels would make on the railway track would propagate along the track, faster than the moving train itself and reach the Native American’s ear. Sound also travels through liquids, such as water.

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