Experiment at Home

Rising Water

Rising Water

Perform this experiment only under adult supervision.

What do you need?


What do you do?

  1. Add a little water to the plate.
  2. With the help of an adult, place a candle in the center of the plate and light the candle.
  3. Bring the cup down on top of the candle.
  4. Wait and watch: What is happening to the candle? What is happening to the water?

What’s the science behind this?

Fire needs oxygen to burn. When we cover the candle, we smother the flame and deprive it of more oxygen. Once the flame uses up all the oxygen in the cup, the candle goes out.

As the candle burns, it uses oxygen and releases carbon dioxide – but it still uses more oxygen than the carbon dioxide it releases. When the number of molecules in the air decreases, so does the air pressure. In consequence, the air pressure inside the cup is lower than the air pressure outside.

In addition, the candle warms up the air and expands it. Once the candle goes out, the air cools down and shrinks, and air pressure drops even further.

When the outside air pressure is higher than the air pressure inside, it pushes the water into the cup.

You can also perform this experiment by figuring this out: place a coin on the plate, outside the cup. Can you remove the coin without touching the water?