Tuning Fork Boxes - Kevin

These mounted tuning forks can be used to dramatically demonstrate the phenomena of resonance and beats.  You’ll need:

• 2 tuning forks mounted on boxes
• 1 mallet to strike them
• 1 ping pong ball on a string
• A few plastic combs

This works best on the first floor near the Sound Track.  Set up the boxes so that the holes are facing each other.  One of the tuning forks is adjustable.  Make sure that both of the weights on the adjustable tuning fork are aligned with the lower marks on the tuning fork.

When guests approach, tell them that you are conducting an experiment using sound or tuning forks.  Show that hitting the tuning forks makes a sound.  (It works best to hit the fork directly on the weight.)  They can make observations at this point like that both forks make the same sound, they vibrate, etc.  You can also show how the sound stops when you grab the fork to make it stop vibrating.

Now show what happens when you just hit one of the forks.  Let it ring for a moment and then grab it to stop its sound.  You can even pull it away from the table.  The other fork will still be ringing.  What’s happening?  We didn’t hit that fork but it’s still making sound!  The guest might make observations like the first one is making the second one vibrate or the sound is hitting it and making it move.  Your next tool can explore if that second fork is moving.

Have the guest hold a ping pong ball on a string so that the ball is balanced against the second tuning fork.  Now hit the first fork.  It will make the ping pong ball dance.  I like to give plenty of time to let the guest wonder before prompting them.  They usually start making claims on their own.  I try to follow the guest at this point - they might say the vibrations are going through the table.  They can try holding them in the air (with a friend) to test this.  They might want to try changing the position of the weights.  I’ll ask what they think is going on and restate their observations and claims but stay away from telling them what is happening. 

If the guest is engaged, I’ll say there’s another experiment we can try.  First show them what happens when you hit both of the forks (answer: not much).  Now move one of the weights so that it’s aligned with the higher mark on the tuning fork.  Hit both of the forks. The sound has changed.  Sometimes they think one is louder, but usually they notice that it’s making a pulsing sound.  I tell them that there is a cool way to visualize what is happening.  Hold up one of the combs and look through it.  Hold it above one of the forks and say, “Pretend this is the first sound.”  The other comb is the second sound, very similar but slightly different.  Now when you hold them on top of each other, they make a new pattern.  Strike the forks separately connecting them to the visual of the fork.  Now hit both and put the combs on top of each other (i.e. one in front of the other so that you’re looking through the teeth of both).  Let the guests experiment with the forks and ask what they think is happening. They might say something about sound waves which makes a great segue to direct them to the oscillating guitar strings to continue their exploration of sound!