Drinking candle

Drinking candle

Sometimes candles need a drink too

Try this and find out why!

What you need:

  • Water
  • Saucer or shallow bowl
  • Tea light or small candle
  • Lighter or match
  • Glass
  • Food colouring (optional)

How to:

Ask an adult for help using the lighter or matches. Make sure you carry out the experiment away from flammable materials.

  1. Pour water into the saucer or bowl to around 1cm deep. Adding a couple of drops of food colouring will make the water easier to see.
  2. Place the tea light or small candle in the centre of the bowl, making sure that the wick doesn't get wet.
  3. Use the lighter or match to light the candle.
  4. Turn the glass upside down and place it over the candle.

What happens to the water? What happens if you use more than one candle?

What's happening?

When the candle burns inside the glass, the air inside the glass gets warmer.

Warm air takes up more space than cool air. The air inside the glass pushes against the glass. Expansion of the warm air causes the air pressure inside the glass to increase.

Air wants to move from an area of high pressure to an area of low pressure. The high pressure air inside the glass tries to escape to the lower pressure air outside the glass. You can see little bubbles in the water around the bottom of the glass.

The candle needs oxygen to burn. It soon uses all the oxygen inside the glass. When the oxygen runs out, the candle stops burning.

Now the candle is out, the air inside the glass cools down again. The air pressure inside the glass is now lower than the air outside the glass.

Some of the higher pressure air outside the glass tries to get to the lower pressure air inside the glass. This forces water into the glass.

When water enters the glass, the space for air inside the glass is smaller. This cause the air pressure to rise. The water keeps going into the glass until the air pressure inside the glass is the same as the air pressure outside the glass.

Curriculum information