How to make a Barometer

We have looked at air pressure with eggs before. This experiment shows you how to make a Barometer which measures air pressure in the air around you.

What you need:

a jar or coffee can

an elastic band

a pin or cocktail stick

tape

glue

straw

paper

Instructions

• Blow up the balloon a little bit, the more air in the balloon, the greater the pressure outwards which is what makes the balloon blow up.

• Let the air out of the balloon and cut the tie end off.

• Stretch the balloon tightly over the jar or can and either sellotape or use the elastic band to fix it tightly.

• Tape or glue the end of the straw to the centre of the balloon and sellotape the pin or cocktail stick to the end.

• Tape some card behind the barometer and mark where the pin is.

• Leave for a few days and note any changes. Record what the weather is like each day and how that affects the barometer.

The Science Bit

When the straw tilts up, the air pressure is high as the air pushes down on the balloon. When the straw points down the air pressure is lower which makes the air in the jar push up on the balloon.