In this activity, students simulate the tuning of a stringed instrument with taut elastic bands.
Small, simple changes in the tension of an object produce changes in the pitch of the sound they produce.
Adding a weight to a hanging elastic band increases its tension. This in turn will increase the pitch, resulting in a higher sound. A looser band has more give, slowing down the vibrations that oscillate through it. A tighter band has less give, increasing the vibrations that oscillate through it.
On a guitar or violin, there are three ways to change the pitch of a vibrating string (length, diameter, and tension). Since adjusting the length and diameter of the string is impractical when tuning the instrument, musicians vary their tension instead. Guitars and violins have winch-like mechanisms which allow the strings to be wound tightly with the simple turn of a knob and hold the added tension, preventing slackening.
On a guitar or violin, the strings themselves don't make much sound. The vibrations from the strings are transferred (through a "bridge") to the box or body of the instrument, which amplifies the sound and makes the air inside and around the instrument vibrate.