Material:

• A cellophane square measuring 5 cm across

   Hold the cellophane tightly between the thumbs and index fingers of your hands.

   Raise your hands so that the cellophane is right in front of your mouth. Just like Yoyo in the drawing.

   Blow fast and hard onto the stretched piece of cellophane.

What's going on?

As soon as your breath hits the edge of the cellophane, you hear an awfully loud sound. (If you didn't hear an awfully loud sound, adjust the distance between the cellophane and your lips.)

The air is travelling quickly, and it makes the edge of the cellophane vibrate. Because the cellophane is so thin, it vibrates ultra-fast. The more frequent the vibrations, the higher the sound.

Materials:

• A piece of string 120 cm long

• A teaspoon

   Make a simple loop in the middle of the string by passing one end of the string over and then under the other end. Tighten the loop a bit, but don't tighten it so much that it forms a knot. You should have an opening that's a couple of millimetres across (see the illustration).

   Slide the handle of the spoon into the loop. Tighten the loop so that it grips the spoon. The round part of the spoon should hang down below the handle. Put each end of the string up to each of your ears. WARNING: Don't put the string right inside your ears. Slowly swing the spoon so that it bangs on the edge of a table.

What's going on?

The sound you hear sounds nothing like a spoon banging on a table. It sounds more like a bell.

The string transmits vibrations from the spoon more effectively than the air transmits them. The strings carries the sound directly to your ears. That causes the ringing sound that you hear.