See the Hidden Shapes of Sound! Exploring Resonance with a Tablet and Water (Air Column Resonance Experiment)
Hello, this is Ken Kuwako, your Science Trainer. Where every day is an experiment.
“Sound” is invisible to the naked eye. But wouldn’t you feel a spark of excitement if you could capture those invisible waves perfectly using just math and experiments? Today, I’m introducing a lesson on “Air Column Resonance.” We’ll combine modern tablet devices with good old-fashioned water and pipes to unlock the secrets of sound speed and wave shapes. Try to picture the invisible “vibrations of the air” in your mind as you read along.
Visualizing “Sound” with Tablets × Analog Experiments
At the Narika Science Academy, we actively introduce experiments utilizing tablets within our science curriculum. Yesterday, we conducted the “Air Column Resonance” experiment using an acrylic pipe and a tablet. The mechanism behind this experiment is simple, yet the science runs deep. We use an oscillator app on the tablet to continuously project a sound at a precise frequency into the acrylic pipe. Then, by raising and lowering a water container connected to the bottom, we change the water level (the length of the closed pipe) inside.
Suddenly, at one very specific depth, the sound jumps out—”WAH!”—becoming surprisingly loud. This is what we call resonance.
Hunt for the “Nodes” and “Antinodes” of the Sound!
If you listen closely, you will find several distinct spots where the volume spikes. We vary the lengths and measure the air column at each of these points.
Inside the pipe, a phenomenon called a standing wave is occurring—it looks as if the wave has stopped moving. Finding the spot where the sound gets loudest means you have located the place where the air vibration is most intense (the antinode). In this experiment, measuring the difference in length between two resonance points allows us to calculate the speed of sound.
[Quiz] Is the Air Spilling Out? The Mystery of “End Correction”
Now, let’s solve a little physics puzzle. When you perform this experiment, you run into a strange phenomenon: the “calculated wave length” and the “actual pipe length” don’t quite match.
One group conducted the resonance experiment and found resonance occurred at 0.415m from the tube opening. They also measured the distance between two resonance spots (half a wavelength) and calculated the full wavelength to be 0.34m.
From this data, let’s deduce what kind of standing wave is occurring inside the tube and calculate the end correction.
If the wavelength is 0.34m, the length of the fundamental vibration (1/4 wavelength) is 0.34 ÷ 4 = 0.085m. The current resonance point of 0.415m is very close to 5 times that number (0.425m). This suggests that the 5th harmonic (the 3rd resonance point) is occurring.
However, while the calculation says 0.425m, the reality is only 0.415m. This gap exists because the sound is actually vibrating slightly outside the exit of the pipe (End Correction).
0.425m － 0.415m ＝ ？？？
So, what is the answer in cm? (The answer is 1cm!) Being able to measure the invisible “spillover” of air by combining experimental values with theoretical ones—that is the real thrill of physics experiments.
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