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Day 11 - Why do Christmas crackers go bang?

Updated Wednesday, 8th December 2010

Dr James Bruce from the Open University's Chemistry Department unlocks the secret to Christmas crackers

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Here's one to share during this year's Christmas dinner...

The bright wrapping of the Christmas cracker contains a cardboard tube. Attached to the side of the tube inside the cracker is a strip of paper. This paper has been treated with a tiny amount of gunpowder – an explosive mixture of potassium nitrate, charcoal and sulphur.

But there’s so little gunpowder that it doesn’t need much heat to set it off. When both ends of the cracker are pulled, the force generates a friction between the paper and the tube, which causes enough heat to set the gunpowder off.

The tube helps contain the explosion of such a small amount of gunpowder and magnifies the noise, making that nice loud bang that signals the start of a Christmas dinner.

And there you have it! An explosive Christmas cracker!

 

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