You hear sound waves when the air vibrates your ear drum. Sounds have a higher note or pitch when they beat faster. The waves are closer together. Look at the four bottles on the left. The more you fill them up with liquid the less air there is to vibrate. If you blow across the top of the bottle the note will get higher as you add more liquid. (See video)

The whole class can make a fun flute from a plastic drinking straw by following these instructions:

1. Chew on one end of your drinking straw to flatten it.

2. Cut the end into a pointed beak shape with scissors.

Blow hard on the flat end of the straw to make music. Experiment by cutting small pieces off of the end of the straw, then making a sound after each piece is removed. The sound pitch becomes higher and higher as your drinking straw flute gets shorter and shorter.

Explanation: The number of times an object vibrates in a set period of time is called the frequency of sound. As the frequency increases, the pitch of the sound gets higher. Shortening the length of the drinking straw makes it vibrate at a higher frequency. This gives you a higher-pitched sound.

When you play a flute, why does the pitch get lower as you cover more holes. (Answer is because the air has more room to vibrate, and its frequency is lower).

Bring in a flute, and play it, and ask why the note changes when you cover the holes. Then show by blowing into a bottle and filling up with liquid (see video), and then give everyone a straw and scissors and ask them to make the notes change. Then they can draw the diagrams at the bottom of this page. You (or Bijen) need to put these diagrams on the board or have a poster prepared. They will need a ruler, a pencil, and one coloured pencil (and paper).