Take a deep breath

Here's a neat way to measure how much air your lungs can hold.

What you need:

• Water
• 2 litre plastic bottle
• Deep bowl  - washing up bowls are ideal, but make sure it's clean!
• Masking tape
• Measuring jug
• Beaker
• Flexible plastic tubing
• Marker pen or biro

How to:

1. Attach a strip of masking tape to the plastic bottle, from bottom to top.
2. Fill the measuring jug with 50ml of water and pour the water into the bottle. Mark the water level on the tape.
3. Repeat until you've marked right up to the top of the bottle - the bottle should be full.
4. Fill the washing up bowl with around 10cm deep of water.
5. Completely cover the mouth of the bottle with your hand, so no water can escape.
6. Invert the plastic bottle into the bowl of water.
7. Don't remove your hand until ALL of the mouth of the bottle is completely underwater.
8. Insert one end of the plastic tubing into the water bottle. Hold onto the other end.
9. Take a deep breath in. Exhale into the plastic tubing.
10. Measure how much air is now in the bottle. Count up the number of lines where there is air, not water. Multiply the number of lines by 50 ml.

For example: 10 lines x 50 ml = 500 ml of air. Your lung capacity - how much air your lungs can hold - is 500 ml.

What's happening?

You've just made a spirometer - a device that doctors use to measure lung capacity. Blowing air from your lungs into the bottle displaces some of the water. You replaced the volume of water with the same volume of air from your lungs. This is your lung capacity

Try it on friends or your parents. Do taller people have a bigger lung capacity?  Why does size make a difference?