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Sound Science: Do-Re-Mi with Straws

A musical physics problem from Science Buddies 

Observations and results
Did the shorter straw play a much higher-pitched sound than the longer straw?
The pitch of a sound corresponds to the frequency of the sound wave. The higher the frequency, the higher the perceived pitch. The shorter straw should have made a sound wave with a higher frequency than the longer straw, and so the shorter straw should have made a higher pitch than the longer straw.
In fact, because the shorter straw was half the length of the longer straw, the shorter straw should have produced a frequency that was twice the longer straw's frequency. (This is based on a mathematical equation that describes how the frequency produced in an open cylinder is affected by the cylinder's length, where the frequency equals the velocity of sound—which should be constant—divided by two times the cylinder's length. See the "More to explore" section for resources on this.) When one sound wave is twice the frequency of another sound wave, the pitches are one octave apart. For example, the musical note middle C has a frequency of 262 Hz, and the C note one octave above this has a frequency of 524 Hz (or two times 262 Hz). However, you may have found that it can take some practice using the straw instruments in this activity to produce a constant, single note.
More to explore
Sound Waves and Music, from the Physics Classroom
Air Column Resonance, from HyperPhysics
Physics of Music—Notes, from Michigan Technological University
Fun, Science Activities for You and Your Family, from Science Buddies
Do-Re-Mi with Straws, from Science Buddies

This activity brought to you in partnership with Science Buddies

Science Buddies

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