By | May 4, 2015

What you’ll need:

  • A balloon
  • Scissors
  • A jar
  • A rubber band
  • Tape
  • A straw
  • A piece of card
  • A marker (felt pen)


  1. Cut the top off the balloon (the part which you blow into).
  2. Stretch the balloon over the top of the jar and hold it in place with a rubber band.
  3. Place the straw across the top of the jar so that one third of the straw is hanging over the edge. Stick the straw to the balloon with tape.
  4. Draw three lines on the piece of card that are about half a centimetre apart from each other. Label these lines as high, moderate and low.
  5. Tape the card against the back of the jar so that the straw points to moderate.
  6. Put your barometer on a flat surface somewhere inside.

What’s happening?

When there is low air pressure the balloon should expand out and the straw will point down. This is because the air inside the balloon now has relatively more air pressure compared to the air outside, it pushes the balloon out as a result.

Dissolving Sugar at Different Heats

When there is high air pressure the air on the outside will push the balloon into the jar and the straw will point upwards. The air inside the balloon now has relatively less pressure, this pushes the balloon inwards as a result.

In general, high air pressure indicates fair weather while low air pressure indicates that bad weather is more likely. Although forecasting the weather isn’t an exact science and can be very difficult at times, give it a go and see how accurate you are.

Combine your results with wind speed, wind direction and rain fall for a full weather report.