Why Does the Water Rise?
You’ll have to watch closely and use everything that you know about air in order
to explain the mystery of the rising water.
Materials
- Candle and matches
- Pie pan or dish
- Juice bottle
- Water
- Food coloring
This experiment requires the use of matches... and that means adult
supervision.
Experiment
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.
Credit: Steve Spangler Science
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