Pitches of sounds

The faster objects vibrate, the higher the pitch of the sound. If you play a musical instrument you might already know how to make a sound have a higher pitch.

If it's a string instrument, you'll know that thin, tight, short strings make higher notes whilst thicker, longer, loose strings make lower notes. The higher notes are due to faster vibrations.

You can try this with milk bottles. Fill the bottles with different amounts of water. If there is more water and less air in a bottle, less air will vibrate and the sound will be higher pitched.

If you play a wind instrument, you'll know that blowing into a long column of air makes a deeper sound, whilst shorter columns of air vibrate faster to make a higher sound.