Alright! I’m sort of back. With science, of course.

Learning is great. So I’m going to do it everyday. Or at least try to. Let’s start with learning about sound.

I have these cheap speakers next to my laptop, and when I write or read or do school work I usually listen to music. Then I started to wonder. How does sound work? What even is it?

There must be some vibration that leads to air (?) reaching my ear. I’m not even gonna try to get into human anatomy or how hearing works. Anyways, the vibration that reaches my ear. That vibration must be at some frequency, right? I mean sound is just vibration, right? It makes me think of sound waves:

Well, that doesn’t exactly help. I mean maybe a little. But I have a feeling there’s a little more to sound…. yeah, I’m still confused on how words and drums and speakers and the universe works. I think amplitude is the “oomph” of sound. Let’s go to Wikipedia.

I’m a meteorology major, so let’s look at the physics side of things. Sound is a vibration that propagates through an acoustic wave. Neat. What’s a vibration? A phenomenom where oscillations occur about an equilibrium point. Well that doesn’t tell us much about speakers or sound or drums or whatever. So, let’s break it down with an example.

Let’s say you hit a drum. It vibrates the material that makes up the drum, which shakes and makes a sound. Well, the banging produces a sound? Let’s say you slam a desk drawer. I recommend not actually doing this. It produces a sound once you slam it. It vibrates air, which is sound. Or brain receives the wave at a certain frequency and amplitude and words or a beat or whatever.

That’s not good enough. What frequency can we hear? What even is frequency? Frequency is defined as this:

Where t is the period (time taken to complete one cycle of an oscillation). So the inverse of that must be s-1 or Hertz (Hz), or the number of occurrences of a repeating event per unit time (cycles per second).

The time it takes for the ball to get back to the the black dot after going right then left is one period. The frequency is one over that. If it makes 1 cycle in 1 second, the frequency is 1 Hz. Or 25 cycles in 60 seconds, the frequency is .417 Hz. This is similar to how sound waves work, except the frequency is given by the wavelength and the velocity at which the wave propagates (v).

How does this relate to sound, I hear you asking? Well sound waves, seen in the first picture, travel at a certain speed and have a wavelength, so we can find the frequency. Higher frequencies produce higher notes, and lower frequencies produce more rumbling sounds.

Speakers have a motor with a diaphragm (thing that converts vibration to sound) which the couples the motor’s movement to the motion of air (sound). What frequencies can we hear?

The range that we can hear is from 20 Hz to 20,000 Hz. So in other words, when we hear, the air is vibrating (oscillating) really fast. From 20 cycles per second to 20,000 cycles per second. The sound wave must be moving really fast or have a very small wavelength.

But what about sounds like thunder, something intangible? Thunder is sound caused by lightning. Lightning channels are really really hot. From 20,000 to 30,000 Kelvin (167 times the boiling point of water!). The hot channel causes the air to expand rapidly (pV = nRT). Air expanding rapidly causes a shock wave (wave of pressure in a medium such as air or water). The shock wave propagates in a manner different from regular sound waves (faster), but still perceive the sound it produces as thunder.

For a better illustration, see shockwaves visualized. Sometimes the thunder is too far away to hear. The energy of the shock wave is expended to the medium in which it travels in the form of heat energy. By the time it reaches us, all the energy was expended to the environment, so we can’t hear anything.

I hope you enjoyed this! See you next time.