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The Heatproof balloon

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science activity showing heat transfer


2 Balloons, Tealight, tap/water


Light a candle

Blow up a balloon
Try holding it in the flame - what happens?

Now add a little water to the balloon, and then blow it up.
Hold the part of the balloon that is covered with water to the flame.

Obviously be careful with the candle, and as the balloon may burst, do the experiment away from anything electrical, or which may be damaged by getting slightly wet. Don't leave the balloon over the candle for more than a few tens of seconds or the water could get very hot.
What may happen

You should find that the empty balloon pops immediately, but the balloon with the water is stable for ages over the flame.

Why does it happen?

The candle is a source of heat and will add heat energy to any object it touches.

If you put a normal balloon over a candle, the candle adds a lot of heat energy to the rubber until it heats up to the point at which it fails, and the balloon bursts, But

If the balloon has some water inside, the heat is transferred to the water which takes a long time to heat up, so the rubber never heats up enough to fail.


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