[neilep (OP)]

What exactly makes the ' POP' sound when burning wood and what is also making the ' whining ' sound ?...how are the sounds made ?..I expect it is the wood and perhaps it drying out maybe ?.....

for the record..I do NOT burn stuff in my garden..but clearly one of my neighbours do !..I hate it when they do !!

[Karen W.]

The popping is usually pitch and the other sound usually is the moisture being heated and evaporated.. Yes I agree I have had full loads of laundry drying when I come home they are filled with smoke from the neighbors burning!!

[paul.fr]

The popping is usually pitch and the other sound usually is the moisture being heated and evaporated.. Yes I agree I have had full loads of laundry drying when I come home they are filled with smoke from the neighbors burning!!

just to add to Karen's reply.

it can also be the oxygen and water mix that is in the wood that is burning, also the wood sap.

different woods and the relative dryness of the wood will act differently, for example create more smoke.

i knew being a joiner would prove useful one day!

[Karen W.]

LOL!! I have also noticed that green wood pops alot, but this may be because of moisture content also! 

[Bored chemist]

"It can also be the oxygen and water mix that is in the wood that is burning"
I doubt that since neither oxygen nor water burn. My best guess is steam escaping from within the wood as it heats up.

[chris]

This is correct. Wood is by its very nature a series of tiny hollow tubes, called xylem, which during life carry water from root to shoot. This means that a newly-cut piece of "green" wood potentially contains a large amount of water locked away inside.

When you heat the wood on the fire the water vapourises and significantly increases the pressure inside the material. This pushes water along these same tubes that carry it during the life of the plant, which is why you often see the end of a damp stem bubbling, hissing and issuing steam, even though that part of the wood is not actually in the fire. Each of these tubes behaves like a miniature musical wind instrument, and some of them are the right length to produce sounds we can hear.

Some plant and tree stems also contain air-spaces at the centre. It's usually a feature of fast-growers, and bamboo is a very good example; elder trees also do something similar - the inner part of the stem is soft and spongy. This makes the material much lighter so it's easier to support.

But if you look at a bamboo cane that's been split lengthways you'll see that these air-spaces are not connected together. They are sealed at intervals of 15-30 centimetres at the point where leaves would have emerged from the steam. As they are not in communication with each other each of these air-spaces behaves like a sealed pressure cooker. So when you "cook" the wood the gas inside (including water vapour) heats up and increases in pressure. Eventually the pressure becomes so great that it tears the fabric of the wood apart, and you hear a bang or "spit".

This is actually very similar to the way that popcorn works because the individual maize kernals are sealed by a highly crystalline cellulose pericarp "wrapping". So when you put your popcorn in the microwave, or a bowl of hot fat, the gas inside the corn becomes superheated and eventually rips open the pericarp shell, turning the corn inside out as it does so. Hey presto, Butterkist delight and a pleasing popping sound. Music to hungry ears!

Chris

[neilep (OP)]

Wow..THANK You Karen Paul, BC and extra thanks to Dr Chris for the wonderful explanation (I am sure the others won't mind my singling you out for extra ' thanks'

I suspected it was moisture related but your explanation dots the 'i's and crosses the 't's.

Very interesting about the nature of the 'Popping '..THANK YOU

[Bored chemist]

That talk of popcorn is making me hungry. I did once hear that bamboo got it's name from the bangs and booms you get when you burn it. I haven't checked this, but it's an interesting thought.

[moonfire]

Oh, just for your interest Neilsy...they have candles now with wood wicks to give you the effects of wood being burned so you can hear that marvelous sound!  LOL

[neilep (OP)]

Oh, just for your interest Neilsy...they have candles now with wood wicks to give you the effects of wood being burned so you can hear that marvelous sound!  LOL

Hi LO *giggles*

really ?..that's well cool...or hot !!....whatever !!...me wants them candles and me wants them now !!...

I also want popcorn to share with BC...and the rest of ewe lot of course !!

[Karen W.]

OOOHH POPCORN SOUNDS YUMMY! I want some TOO!

 I like the crackle of a wood fire and I like to smell the sap as it heats up and pops and smells so nice. Now a large yard or brush fire is way different!