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Try This Activity At Home!
Palm Pipes
Source: Square Wheels, an Exploratorium Science Snack Book
- Hacksaw
- 1/2 inch PVC pipe, about 6 1/2 feet long.
- Centimeter ruler
- Sandpaper
- Permanent marker pen
- Several friends
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Cut a piece of PVC to each of the 15 lengths listed below.
Note Length (cm) Frequency (Hz) F1 23.6 349 G1 21.0 392 A1 18.7 440 B flat 1 17.5 446 C1 15.8 523 D1 14.0 587 E1 12.5 659 F2 11.8 698 G2 10.5 784 A2 9.4 880 B flat 2 9.2 892 C2 7.9 1046 D2 7.0 1174 E2 6.2 1318 F3 5.9 1397
- Smooth the edges of the pipes with sandpaper.
- Label each pipe with the musical note corresponding to its length. The numbers next to the note refer to the octave of the note. (The first note in the list is the F above middle C.)
- Play the songs below by gathering a group of people, distributing one pipe to each person, and having each player sound his or her pipe at the right time. Before you begin, each person should practice making a good tone by holding the pipe vertically with one hand and banging the bottom end into the palm of the other hand. It's important mot to cover the top end of the pipe.
Playing a song is easiest if there is one player per note, but if you have too few people, you can have one or more players take responsibility for two pipes. If you do this, however, make sure a person doesn't have to sound two different notes in a row. If you have many more people than notes in a song, you can have some players play pipes that are an octave lower than the ones called for. For example, when the F2 pipe for "Twinkle, Twinkle, Little Star" is being played, another player can play the F1 pipe at the same time.
It may be helpful to have one person act as conductor.
Mary Had a Little Lamb
(Pipes C1, D1, E1, and G2 four players)
E D C D E E E D D D E G G
E D C D E E E E D D E D C
Jingle Bells
(Pipes C1 through G2 five players)
E E E E E E E G C D E
F F F F F E E E E E D D E D G
E E E E E E E G C D E
F F F F F E E E E G G F D C
Twinkle, Twinkle, Little Star
(Pipes F2 through D2 — six players)
F F C C D D C B B A A G G F
C C B B A A G C C B B A A G
F F C C D D C B B A A G G F
My Country 'Tis of the Thee (America)
(Pipes E1 through D2 — seven players)
F F G E F A A B A G F G F E F
C C C C B A B B B B A G
A B A G F A B C D B A G F
Twinkle, Twinkle, Little Star
Pipes F2 through E2 — three players on melody (M), and three player on harmony (H).
M: F F C C D D C B B A A G G F
H: C C A A B B A G G F F E E C
M: C C B B A A G C C B B A A G
H: A A G G F F C A A G G F F C
M: F F C C D D C B B A A G G F
H: C C A A B B A G G F F E E C
What's going on?
When you hit the open end of the pipe against your hand, air molecules in the bottom of the tube are squeezed together. This starts a process that takes four trips up and down the tube.
The molecules that have been squeezed together, in turn, squeeze the molecules next to them, and so on. In a sort of domino effect, the pulse of compression (high-pressure air) travels up the tube. When the pulse of compression reaches the top of the tube, it expands outward into the air around the tube. In the process, some air molecules overshoot the end of the tube, producing a region of expansion (low-pressure air) in the top of the tube.
Air molecules just below the area of expansion rush upward to fill it, creating a pulse of expansion that travels back down the tube. When this pulse reaches the bottom, it reflects off your palm and travels back up the tube as another pulse of expansion.
When it reaches the top, some air from outside the tube rushes into the low-pressure area, creating an area of compression, which travels as another pulse back down the tube.
When this pulse of compression reaches the palm of your hand, it reflects, and at this point the whole process repeats itself.
This four-part cycle corresponds to one wavelength of sound, or one single vibration. A series of these repeated cycles is the source of the sound you hear when you "play" one of the pipes.
The length of tube affects the note that the tube produces. Because the speed of sound waves is the same in all the tubes, the length of the tube has a direct effect on the time it takes for a compression-expansion pulse to make its four transits of the tube. The longer it takes for a pulse to complete its cycle and start over again, the fewer the cycles, or vibrations, per second, the lower the frequency of the sound, and the lower the musical note.
Going Further
You can calculate the approximate frequency of sound that any length of pipe will produce. The velocity of a sound wave is equal to its frequency time its wavelength. Put another way, frequency equals the velocity divided by wavelength. The velocity is 350m/s in normal room air temperature. The wavelength can be obtained by multiplying the tube length in meters by 4 (the number of transits). Therefore, if you divide 350m/s by a tube's wavelength value, you obtain the approximate frequency in cycle per second, or hertz, of the note the tube will produce.
The diameter of the tube affects the frequency, also. The reflection of the sound wave doesn't occur exactly at the open end of a tube but happens at a point slightly beyond the end. The larger the diameter of the pipe, the farther from the end the reflection occurs. To more accurately estimate the value for the frequency, add .03 of the inside diameter to the length of the tube.