Monday, November 24, 2014

Candle/Air Pressure Experiment

Ever wonder how you can "magically" get water to rise up a glass?  Now you can do it yourself through this simple experiment.  Begin by lighting a small candle.  Fill a bowl of water colored by the food coloring of your choice.  Place the candle in the bowl of water, making sure the candle is tall enough such that the water level is below the candle wick.  See below.

Now take an empty class or jar (canning jars work great) and use it to cover the candle.  The flame will use up the remaining oxygen in the jar and go out.  As the flame diminishes and goes out, watch the water level in the jar.  It will slowly start to rise up the jar!  Very cool!  See our video below.

So why does the water appear to break the theory of gravity and rise?  The candle quickly heats the air inside the jar.  The air has nowhere to go.  As the flame diminishes, the air temperature quickly drops, and then drops even further as the flame goes out.  Colder air compresses into a tighter space and the air pressure is greater than the force of gravity pulling the water down.  Therefore, the water level inside the jar continues to rise!  If we had a taller candle, we could have tested how far the water level would rise.  Unfortunately all of our taller candles were larger than the jar so we couldn't test this.  Despite this, it was still a very cool science experiment.

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