# Science Experiment: Sound Waves and Pitch

Hi kids, parents, and teachers! Science projects and experiments can be fun. However, be sure to always have a parent or teacher supervising to make sure things are safe!

Purpose: This activity will help you understand how changing the rate of vibration can vary the pitch of a sound. For more on pitch and sound see Sound for Kids.

Materials
• cardboard pencil box (without a lid)
• rubber bands (different thicknesses and lengths)
• wooden dowel
• ruler
• notebook paper
Procedure
1. Arrange the assorted rubber bands from thinnest to thickest.
2. Place the rubber bands in order (on the box) from thinnest to thickest
3. Pluck each rubber band, make observations, and record your findings on notebook paper.
4. Place a ruler (on its edge) across the pencil box to form a bridge. The rubber bands will become tighter as they are pressed down.
5. Pluck each rubber band; then, observe and record your findings.
6. Move the ruler "bridge" off center to the left or to a diagonal position so that one side of each rubber band is shorter than the other side.
7. Pluck each rubber band, observe, and record your findings.
Conclusion/Questions:
1. Does each rubber band produce the same sound without the bridge in place? Why or why not?
2. What change if any, does the ruler make on the sound produced?
3. Compare and contrast the sounds produced. Original rubber band arrangement - Ruler placed in the center - Ruler placed off center
4. How does the length of the rubber band relate to frequency (the number of vibrations over time)?
What's Happening?

Just as the strings inside a piano create different sounds, so too will the rubber bands. When the rubber bands are plucked in order, from thinnest to thickest, the sound will gradually change from a high pitch to a low pitch. When a ruler "bridge" is added, it absorbs some of the vibrations. The length of the rubber band that is able to vibrate becomes shorter. The shorter bands will vibrate faster, producing a higher pitch. By moving the ruler "bridge" off the center point, one side of the rubber band becomes short and the other long. The longer length of the rubber band makes a low, long, heavy sound and vibrates at a slower rate of frequency. The shorter length of rubber band makes a high, short sound and vibrates at a faster rate or frequency.

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1. Does each rubber band produce the same sound without the bridge in place? Why or why not?

No, the pitch of the sound changes from a high pitch to a low pitch. The density of the rubber bands is different.

2. What change if any, does the ruler make on the sound produced?

The ruler absorbs some of the sound and makes the length of the rubber band shorter. The shorter length causes the band to vibrate faster and produces a higher pitch.

3. Compare and contrast the sounds produced. Original rubber band arrangement - Ruler placed in the center - Ruler placed off center

The original rubber band arrangement will produce lower pitched sounds than those made when the ruler is placed in the center. If the ruler is placed off center, the longer side will produce low, long, heavy sounds, while the shorter side will produce the high, short sounds.

Reference: NASA SciFiles

More Sound Experiments:
Sound Waves - See how sound waves propagate.
Sound Vibrations- Learn about sound by making a kazoo.

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