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Re: [Phys-l] Crackling of a fire

On 01/22/2009 12:41 PM, asked:

Why, when you put a log on the fire does it 'pop, crack and crackle'?

1) There's no doubt that water in the wood plays a role.
Wood that is mechanically strong(*) but wet is spectacular.

2) There's no doubt that organics ("resin") in the wood
also play a role, even in dry wood. To verify this,
pound a nail into the wood and remove it. The hole will
emit a jet of gas. You know it's not water vapor because
it burns when it hits the air.

(*) Note I said "mechanically strong". I almost said "hard" but
that is confusing because of the term "hardwood". It's a crazy
term; balsa is, after all, a hardwood.