Why Does the Water Rise? You’ll have to watch closely... email to friend
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1. Fill the pie pan 3/4 of the way with water and add 3 drops of food coloring. Place the candle in the middle of the pan.
2. Light the candle. Think about what a candle needs to burn.
3. Cover the candle with the jar. What invisible thing is inside the bottle? Carefully observe what happens to the water level in the bottle. What happen to the candle flame?
4. Repeat the experiment several times until you can write down or draw a picture that explains why the water level rises.

How does it work?

The candle needs oxygen to burn. When you cover the burning candle with the jar, the flame eventually goes out as soon as all of the oxygen is used up. Since there is no more oxygen under the cup, the rest of the gases (nitrogen, argon, carbon dioxide, and others) are exerting less pressure compared to the atmospheric air. The greater atmospheric pressure on the outside of the bottle pushes the water in the pan up into the bottle.

However, there is another important factor that accounts for the rise in water level. The candle flame heats the air in the bottle, and this hot air expands. Some of the expanding air escapes out from under the bottle — you might see some bubbles. When the flame goes out, the air in the jar cools down and the cooler air contracts. The contraction of the air draws the water up into the bottle.