Guitars make sound because of two things called VIBRATION and AMPLIFICATION. Here’s how it works. To conduct this science activity, you will need the following supplies:
3. A pebble, marble, or other small object
4. Two shoeboxes with lids
6. Two rubber band
7. Four pens with lids
When you pluck a guitar string, the string vibrates, which means it wiggles back and forth really fast. That’s called vibration. Try it:
Take one of the shoeboxes. Make sure the lid is on top of the box. Wrap a rubber band around the box. Lay pens underneath the rubber band, spreading them out from each other so that the rubber band is raised up in the air a little bit in between them. Tuck the rubber band underneath the clippy part of each pen lid, so they hold the rubber band in place. Grab the rubber band between the pens, pull on it, and then let go. Watch the string vibrate for a moment and then stop.
The vibration of the string causes a tiny wind in the air around the guitar. The wind is so small that you can’t even feel it. The wind ripples just like water ripples when you drop a pebble into it. Try it:
Fill the bowl with water. Drop a pebble, marble, or other small object right in the middle of the bowl. Watch the surface of the water ripple.
When you pluck a guitar string, the air around the guitar ripples just like the water, except that you can’t see it, because air is invisible. The rippling air travels to your ear like a tiny wind, and it beats on your eardrum, just like the rippling water beats on the edge of the bowl. That’s how you hear the guitar string when it’s plucked. The harder you pluck it, the bigger the vibration in the string, and the louder it sounds in your ear. However, plucking on a guitar string would be very quiet, even if you plucked it really hard, without amplification. Amplification happens when the rippling wind bounces around, getting bigger and bigger, before it hits your eardrum. That’s why guitars have holes in them. The rippling wind goes down into the hole, bounces around inside the guitar, and then comes out of the hole bigger and louder. Try it:
Take the lid off the second shoebox. Poke a hole in it with scissors on a pen. Stick the scissors inside the hole, and cut around it, making it bigger, until it looks like a hole in the top of a guitar. Stick the lid back on the shoebox. You should now have a box with a hole in the top. Wrap a rubber band around the box so that it lies across the hole. Place pens underneath the rubber band, one on each side of the hole, and tuck the rubber band under the clippy part of each pen lid, so the rubber band stays in place. Push down on the pens with your hand so they don’t lift up when you pull on the rubber band. Then pull the rubber band and let go.