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For my experiment, I attached three different sized balloons with their tops cut off to a balloon pump. Each balloon represents a different type of vocal cord. The widest one represents an adult male's, the second is a male adolescent's and the last, and smallest  represents a child's.

My hypothesis is that by stretching these balloons with clamps that are attached to either side of the cut off end, and pumping air into the balloons, different pitches can be attained. By stretching the balloons farther, the sound should be higher, a bigger balloon should produce a higher pitch. The reason for this is that there is less room for the sound waves* to go through, so they will go through slower, creating a higher pitch. Whereas if there is a smaller opening the  sound waves will go through much faster, so a higher pitch can be attained.s

*see info page