Transforming Electricity Into Sound

Today we looked at how electricity can be transformed into light, heat, motion, magnetism and sound. 
As we all know sound is all about vibrations, from the source to the air and finally to our eardrums.  So how does electricity transform into sound?

The example of lightning and thunder is a good one.  As lightning strikes, an electric charge shoots through creating heat in the air around it.  This heat caused the air to expand and contract creating an explosion of sound... thunder. 

A while ago the toothbrush company came out with a fun little toothbrush that plays songs.  While you can hear the music and the words just by holding the toothbrush, you can really hear the music while brushing your teeth, of course because the vibrations produced when the battery circuit is turned on travel along the toothbrush and through your teeth to your eardrum.  But how else could we transfer these vibrations so that more than one person can enjoy the music at one time?  Simple we find a conductor.  We tried a few things; the large metal bowl shown in the video above, a plastic ice cream bucket and our own heads/faces. 

We discovered that the metal bowl acts like a megaphone, taking the vibrations and 'radiating' the sound waves out through the large opening on the other side.  If we placed the toothbrush against the outside edge of the bowl it wasn't as loud as if we placed the toothbrush on the very bottom of the bowl. 
It also seemed that the plastic ice cream bucket was the best conductor and played the music the loudest. 
And our heads; we placed the back of the brush on the side of our face just in front of the ear.  This was a very good conductor but mainly to one person at a time.  Mike found that the volume could be controlled by different spots on his head however I didn't notice a difference.  You can also place the back of the toothbrush over the entrance of one nostril, then plug the other side and open your mouth and voila, you are conducting a sound that is not your own through your body, crazy!

Anyways, it's a fun little experiment.  Unfortunately the clip is very short since the moment I want to record video it sucks up all the battery and the camera dies.