We will need:
- 2 candles, identical
- 2 tall bowls, higher then the candles and identical,
- match box, or a cigarette lighter,
- water, enough to fill the bowls.
- Chose a safe spot for the bowls. They will stay there for a while;
- Place the candles inside;
- Fill one bowl with water, leave about 1 in of the candle above the water level ;
- Don't fill the second bowl;
- Light both candles, this is an adult task;
- Wait several minutes;
- Let the wicks burn slow, The candle in the bowl with water will reach the water level;
- Let it burn for a bit more;
The candle in the empty bowl burns normally, as the wick is consumed the wax melt and the candle begins to get smaller.
The candle in the bowl with water burn normally until the wax reach the water level, here, or maybe a few mm before, the candle forms a "funnel", preventing water to contact with the wick, and the candle continues to burn for some time.
Both candles are consumed by the wick flame; if the candles are identical you can observe they burn at same velocity, until the water is placed in the equation.
Everything changes with the water. The candle is consumed because the wax is heated by the wick flame and as consequence the wax melts.
When we light up a candle we expect it to melt, but when we place it "under water" we expect the flame to go out.
But the true is: we can observe the candle burning underwater, it looks like the candle has a survival instinct, just like the balloon, and exactly for the same reason that the balloon doesn’t burst, the candle still burning, and we can see the formation of a "funnel" like a hole, surrounded by wax thin walls, protecting the wick from water.
This happens because the water is a good heat absorber; the heat necessary to raise water temperature by 1 degree is very high.
When the wick transfers the heat to the wax, the wax transfer it to the water, this allows the wax in contact with water to remain cold, and therefore solid.
This system is only in equilibrium for a few sec, or maybe a few minutes, but eventually the water will find its way, even because the walls will eventually collapse with the water pressure (weight) the water comes in and the candle sinks.
This is a demonstration, you can transform this in a experiment or science fair project:
- Use diferent candle types (form, color, thickness, height) which of the candles keeps water away for longer?
- Vary water temperature; this helps the candle to stay lit for longer?
Sometimes things may defy common sense