Sounds can change in shrillness or deepness- that is, in their pitch. When we hear changes in pitch, it means that the sound waves coming to our ears are changing in frequency. Frequency is the number of sound waves that occur in one second. The higher the frequency is, the higher the pitch will be. The lower the frequency is, the lower the pitch will be.

The following activity to determine what the size and shape of a vibrating object has to do with its pitch.

Materials:

• Small box (shoe box, wooden box) open at the top

• Rubber bands that vary in lengths and thickness

Procedure:

1. Using only one rubber band, put the rubber band around the box so it stretches across the opening at the top. Pluck the rubber band.
2. Next tighten the band by pulling it tight from underneath the box. Keep it tight and pluck the rubber band again. Record your observations in your science journal.
3. Place several rubber bands of the same lengths but different widths on the box and pluck each of them. Again, record your observatins in your science journal.
4. Place bands of the same thickness but different lengths around the box and pluck each band. Once more record your observations in your science journal.

Analysis:

1. What is the relationship of the size and shape of the vibrating rubber band to the pitch it produced?
2. List some instruments that prove your conclusion and how each instrument changes pitch.
3. For more information, go to http://www.sfskids.org.