# Fast and Easy Science Fair Projects: Don't Fret

Updated on December 30, 2019

## Changing pitch by varying string tension

Purpose: An understanding of frequency change through an increase in tension on a stretched rubber band.

Overview: Some musical instruments have string that vibrate in order to make sounds, guitar, banjo, violin, harp, to name a few. A string is pulled taut and "plucked." The plucking force applied to the string causes it to vibrate. The mechanical vibrations are converted to sound by our ears.

As a string is pulled tighter by tuning pegs on the instrument, the frequency of its vibration increases and the notes sound higher in the pitch. On a guitar and bass guitar, strings are kept under tension as they are stretched across a long wooden neck. The instrument has "frets" that the musician places his fingers against to shorten the strings that are played, changing the pitch of the sound.

Hypothesis: The more a rubber band is stretched, the higher the pitch it makes when it's made to vibrate.

You need:

• Large rubber band
• Piece of Board about 1 foot (30 cm) long
• Nail
• Small play bucket
• Different size stones
• Scissors
• Hammer

Procedure: Hammer a nail partway into a piece of wood about a foot (30 cm) long and several inches or centimeters wide. The wood should be 1/2-inch (1 cm) thick or more. Don't pound the nail all the way in. Set the board near the edge of a table.

With scissors, cut a large rubber band in half. Tie one end to the nail and the other end to the handle of a small bucket, the kind a young child might use in a sandbox or to play with on the beach.

Drape the rubber band and bucket over the board lengthwise and off the end of the table, so that the bucket hangs in the air.

Put a few stones in the bucket to put tension on the rubber band. With your finger, pluck the length of rubber band that is stretched across the board. Like the string on a guitar or violin, the band will vibrate, producing a sound that you can hear.

Add a few stones to the bucket to stretch the rubber band even more. Pluck the band again.

Is the note sound higher or lower than before? The rubber bad is the Constant in the experiment, and the amount stretched is the Variable.

Results and Conclusion: Write down the results of your experiment. Come to a conclusion as to whether or not your hypothesis was correct.

Something more: 1. Can you add or take away stones from a bucket to match a note from the rubber band to a piano, organ, or guitar in your home? You must have a "musical ear" to be able to tell when a note on your instrument is in tune with the one on the real instrument. If you do not have a good ear for matching notes, have a friend who is taking music lessons help you. Someone who has music training may do best at matching notes.

2. Challenge Project : Our musical scale consists of 12 notes in an octave. Take your project further by constructing 13 rubber band systems, each one stretched to be in tune with a different piano note (the 13th note being one octave higher than the beginning one).

11

3

8

working