Rising Water Air Pressure Demonstration

This straightforward science activity is an excellent demonstration of air pressure! When the lit candle runs out of oxygen, changes in air pressure lead to the water level in the glass rising upwards.

This activity requires adult supervision.

You’ll need

Matches

A pint-sized glass or jar

Egg cup or candle holder

Small tealight candle

Water

Small plate

Food colouring – optional

Instructions

Add a little food colouring to a cup of water and mix thoroughly. Pour the coloured water onto the plate so the base of the plate is completely covered.

Place the egg cup in the middle of the plate and pop the tealight candle on top. Make sure the candle is secure and won’t fall off.

Make a note of the water level inside the glass.

Light the candle ( ask an adult to help ) and place the glass or jar over the top.

The candle will go out when it runs out of oxygen, and you should see the water rise up into the glass.

What’s happening?

The heat of the candle flame increases the air pressure in the glass, which forces some air out. The candle goes out when all the oxygen in the glass has been used up, and the air cools and contracts. The air pressure outside the glass is now higher than inside, so water is sucked into the class until the air pressure is equalized.

Don’t forget to look at my other air pressure experiments too!

 

Last Updated on March 7, 2023 by Emma Vanstone