Ruth Bentley
You don’t need access to a high-tech lab or fancy equipment to do science. After a quick rummage in your house you’ll find everything you need to make your own barometer. Sandals or welly boots? Follow these instructions and you’ll be able find out for yourself!
You will need:
- A balloon
- Scissors
- A glass jar
- An elastic band
- A drinking straw
- Glue (Superglue or craft PVA works best)
- A piece of paper
- Tape
Making the barometer:
1. Gather your apparatus.
2. Stretch the balloon by blowing it up and then letting all the air out.
3. Cut the balloon in half.
4. Turn the top half of the balloon inside out and stretch it over the jar, keeping the balloon as taught as possible to avoid lumps. Secure the balloon around the rim with the elastic band.
5. Cut off the bent end of the straw.
6. Add some glue to one end of the trimmed straw and stick it down so that the end is in the middle of the balloon “lid” with the rest of the straw hanging over the edge of the jar. Congratulations! You have now made a barometer that will measure changes in air pressure.
How does the barometer work?
The air trapped inside the jar stays at a fairly constant pressure as the balloon acts as a barrier, preventing air molecules from entering or leaving. When the air pressure outside rises, the force pushing down on the balloon membrane is greater than the force pushing up, leading the balloon to be forced downwards, tilting the straw upwards. Comparatively, when the air pressure becomes lower than that in the jar, the force pushing up on the membrane is larger so the balloon is stretched upwards and the straw will tilt down.
Using your barometer:
1. Divide the piece of paper into 7 columns and label with the days of the week.
2. Use the tape to attach the paper to an outdoor wall in a sheltered location, positioning your barometer in front of the first column so that the end of the straw almost touches the paper.
3. Use a pencil to record the height of the top of the straw. In a notebook, jot down the time of day and some observations about the weather.
4. Repeat your observations each day at the same time for a few weeks and see if you can spot a pattern between your marks on the paper and the upcoming weather.
What do you notice?
a) High pressure is followed by fair, sunny weather and low pressure by clouds.
b) High pressure is followed by clouds and low pressure by clear skies and sun.
c) Constant pressure is followed by clear weather whereas frequent pressure changes lead to cloud and rain.
Answer
A change in air pressure is a good indicator that a change in weather is on the way. The straw pointing up indicates high pressure which is usually followed by clear skies and sunshine. If your straw is pointing down, the air pressure is low allowing clouds to form more easily. This is a sign to whip your brolly out as rain is likely to be on the horizon.
Ruth Bentley
Featured image by jcc_seveq from Flickr. Image licence found here. No changes made to this image. In article images courtesy of Ruth Bentley. No changes made to these images.
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