What you need

• A small glass bottle
• Water
• An effervescent indigestion tablet

Instructions

1. Pour about 2cm of water into the bottle. Blow across the top of the bottle and listen carefully to the sound it makes
2. Break the tablet in two, and put both halves into the bottle.  Wash your hands while you wait for it to stop fizzing
3. Blow across the top of the bottle again and listen to the sound it makes now

Results and Explanation

Sound travels more slowly through carbon dioxide (the gas given off by the fizzing tablet) than through air, so when you blow across the bottle you hear a lower pitched note.

These experiments have not been specifically safety tested for home use but we believe them to be safe if the instructions are followed. Adult supervision or direction is recommended as appropriate. All experiments are carried out at your own risk.