Science Experiment: Candle and Water

This is an impressive but simple experiment for children. We did it with Alex about two years ago, so it was Max's turn now. But this time I added a bit of a twist though. I spread food colouring on the bottom of tea candle, lighted it and placed it at the centre of a plate with water. The good thing about tea candles, they float and that is very useful for this experiment. Then it can be covered with a jar, but we used a vase for the more dramatic result. The bigger is the jar the more water is sucked into it.

EXPLANATION: The flame burns oxygen and the lack of it makes the candle go out, however, this is not the reason why water is sucked in. The actual reason is hidden in the temperature of the air and how the density of the air changes with temperature. When the candle is heating up the air, it expands getting out of the vase (you can actually see how bubbles of air are coming out in the video). When the candle goes out, the air starting to cool down. Cold air is denser and therefore it needs less space, so it shrinks sucking the water into the vase.