Change in Pitch

Purpose - To make a model that demonstrateshow human vocal cords change the pitch of sound.

Materials hammer

2 nails ruler

woodenblock about 8 inches (20 cm) long

shortand long rubber bands pencil

adulthelper

Procedure

¦ Ask the adult helper to hammer thenails into the board 6 inches (15 cm) apart.

¦ Stretch a short rubber bandbetween the two nails.

¦ Pluck the rubber band with thepencil.

¦ Replace the short rubber band witha long one.

¦ Pluck the rubber band with thepencil as before.

Results The shorter band produces a higherpitched sound.

Why? The rubber bands behave similarly to the two folds oftissue stretched across the larynx or the voicebox. These tissues arecalled the vocalcords. As airpasses through the voicebox, the vocal cords vibrate. The pitch of the soundvaries as the tension changes. When the cords relax, they vibrate slowly andthe pitch is lower than when the cords are tightened.

Change in Pitch