Blowin' In The Wind
The 2012-2013 school year started off with the newest group of Explorers investigating the properties of sound, using supplies as low-tech as they come: drinking straws.
“Sound” as humans perceive it is a matter of interpreting pressure waves in a medium. Eh? When something vibrates, it can cause its surroundings (or medium, which might be air, water, or something else) to vibrate as well. The waves that result from all this vibration travel through the surrounding medium. Inside our ears are specialized bones that pick up these vibrations, and in turn send electrical signals to our brains. Our brains then turn all of this into what we hear as sound.
(This helps to explain, incidentally, why there is no sound in space—without any air or other medium, any vibrations caused in objects just stay put. As a famous movie once said, you can scream as loud in space as you like, but with nothing to carry any vibrating waves, no one is going to hear you.)
Of course, the details of sound get a bit trickier. Different sounds sound, well, different. These differences arise from a couple of factors. The first is intensity—the stronger the vibrations, the louder the sound. Simple enough. The second is the wavelength/frequency of the vibration. Imagine dropping a rock in water and watching the waves all spreading out. The distance between each wave is the wavelength. This is fundamentally tied to the concept of frequency as well. In any given medium (such as air), all waves will travel at the same speed. Waves that are closer together will result in more of the waves reaching your ear in a set time, while waves that are farther apart will cause fewer of them to pass by in the same amount of time.
What effect do the twin concepts of wavelength and frequency have on the sounds you hear? Simple—the higher the frequency (meaning the shorter the wavelength and thus the more waves passing by per second), the higher the pitch of the sound. The lower the frequency (longer wavelengths and fewer waves passing by per second), the lower the pitch of the sound.
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With this understanding in mind, the Explorers went about creating higher and lower pitched sounds by making their own musical instruments. Not fancy musical instruments, mind you, and definitely somewhat on the cheap side, but musical nonetheless, even if they were just straws. Instruments that involve blowing air through or over tubes and holes (such as flutes, clarinets, tubas, and so on) all control the wavelengths and frequencies of the sounds they make by covering and uncovering different combinations of holes. Cover some holes and you create shorter wavelengths (and thus “higher” sounds), while covering other holes will create longer wavelengths (and correspondingly “lower” sounds).
There is one final trick, though. Just blowing air through a tube, as the Explorers discovered with the straws, makes…well, no real sound at all. You have to have a vibration to create a sound wave. In many instruments this is done with a flat piece of wood called a reed. To create their own “reeds” in their straws, the students chewed one end of the straw flat and then trimmed it with scissors to something of a point. Now when they blew into that end (with the trimmed part firmly within their mouths) the trimmed section was free to flap and vibrate. This is dramatically demonstrated if you accidentally or intentionally touch the tip of your tongue to the vibrating part of the straw—the resulting sensation feels a little like a mild electrical shock.
With a nice vibration underway (and a rather, ahem, distinctive sound resulting), the only thing left was to control the pitch of the sound. This was accomplished in two ways—first, by sliding a second straw over the first (moving the second straw back and forth while blowing changed the pitch in a way similar to a trombone); and second, by using a hole punch to make finger holes in the straw (which could then be covered and uncovered to make different pitches, just like a flute or clarinet).
The best part of this activity is that once you get the hang of the whole chewing/trimming/hole-cutting process, you can cheerfully make as many straw instruments as you like even if your first ones wear out. Well, until the neighbors get annoyed, anyway…..
Check out the photo gallery to see some pictures from our first meeting of the year. For more information on this project, as well as shots from previous years, click on the link below.