This activity shows you how to make an aneroid barometer which uses air to measure atmospheric pressure. Generally, high air pressure is an indication of good weather while low air pressure is an indicator of bad weather, so a barometer is a useful tool for predicting changes in weather.
What you need to make a barometer:
- A clean jar or food tin
- Elastic band
- A cocktail stick
- Cut the end off your balloon.
- Stretch the balloon tightly over the jar and fix in place with sellotape or an elastic band.
- Sellotape one end of the straw to the middle of the balloon and the cocktail stick to the end of the straw.
- Place your barometer in front of some card and carefully mark where the pin lies. The barometer will work best if placed somewhere that isn’t likely to be affected too much by temperature changes.
- Record any changes to the pin each day and what the weather is like that day.
Why does this happen?
When we place the balloon over the jar the air is captured underneath at a certain pressure. If air pressure outside the jar is lower than inside, the balloon will expand outwards, causing the straw to point downwards. This happens because the air inside the jar has more air pressure than the outside air.
If air pressure is high opposite happens. The air inside the jar has less pressure than the air outside pushing the balloon inwards.
You should see changes in air pressure just before a change in weather. Can you use your barometer to predict the weather?
Did you know?
Air pressure is most commonly measured in millibars.
Check for air holes or gaps in and around the balloon as these will affect the air pressure.
Don’t leave in direct sunlight as the balloon will also be sensitive to changes in temperature.
Other Weather Investigation Ideas
Make an easy rain gauge using half a plastic bottle. Use a ruler to mark a cm scale down the bottle and record the rainfall each day. Don’t forget to empty your rain gauge daily.
Can you predict the weather using pine cones? Pine cones should close up in humid weather to keep the seeds safe inside.
This post was written by Emma of Science Sparks
Emma is a busy Mum to three who is passionate about science education. You can find Emma’s experiments and activities over at Science Sparks which is full of fun, creative and engaging science based activities for children of all ages, perfect for home or school. Find out more at Science Sparks www.science-sparks.com