The answer lies within the wood itself! Before we look within the wood , let's first learn a bit about fire. Fire comes from a chemical reaction between oxygen in the air and a source of fuel , such as wood or gasoline. Luckily, most sources of fuel don't burst into flames spontaneously, since they're surrounded by oxygen all the time.
Instead, fuel sources must be heated to their ignition temperature for the combustion reaction to occur. At this temperature, the heat begins to decompose the wood's cellulose material. As this happens, the decomposing material takes several forms: volatile gases smoke , char pure carbon , and ash unburnable minerals.
This is what we think of as the process of burning. At the same time, the carbon in the char combines with oxygen in a much slower reaction. You're probably already familiar with char. You can buy it at the store, and it's called charcoal. Charcoal is simply wood that has been heated to the point where most of the volatile gases have been removed.
That explains why charcoal burns with no smoke! When you place a log of wood onto a campfire, it begins to burn. Inside the wood, there are tiny pockets of fluids, such as water and sap. As the wood burns, the fire heats these fluids as if they were in a pan on the stove. The heat from the fire causes the fluids within wood to first boil and then vaporize into steam.
This steam gets trapped in the pocket within the piece of wood. The trapped steam begins to exert pressure on the surrounding wood. Eventually, the wood gives way.
The snap, crackle, or pop sound you hear is the wood splitting along a crevice and releasing steam into the fire. If you've ever tried to use wet wood for firewood, you've probably noticed that it snaps, pops, and crackles much more than usual. That's because of the excess water trapped within the wood! We hope today's Wonder of the Day really got you fired up about learning! Be sure to check out the following activities with a friend or family member:. We hope you share this Wonder with your friends to help them learn why wood crackles when it burns!
That's right! We wanted to make sure we said hello back! Hi, Lilly Claire Lewis! Wood does turn into charcoal when it has been heated to the point where most of the volatile gases have been removed. You can also buy charcoal at the store. There's nothing like a nice crackling fire in the fireplace, Glenn! Thanks for sharing your comment with us! We think it depends on the wood that you're burning.
Some wood branches are small and thin, so they burn more quickly than wood pieces that are thick. Thanks for sharing your thoughts with us, Kate! We bet you'll like camping next year! Hey there, Maxd! We like ghost stories! Check out Wonder of the Day to learn which ones! Thanks for hanging out with us in Wonderopolis today! We do, Stefan! Sometimes the wood makes really loud pops. We learned that's from water and other substances within the wood heating up!
Hey, Wonder Friend! Thanks for guessing tomorrow's Wonder of the Day! We can't wait to see if you're right! Hello there, Derpy-Chan! We think it's great you already knew why wood crackles! Do you like hanging out by campfires? We sure do!! We totally agree, Mrs. Quinn's Class! We do love making and eating s'mores. We know wood comes from trees. And when trees are alive, they stay healthy by carrying water up their trunk through these tiny holes, which are called xylem vessels.
When the tree is chopped down to make firewood, there is still water trapped inside these xylem vessels. There are other ways water can get inside wood. If firewood is left out in the rain, it can soak up water that way. Or sometimes insects make small holes in the wood, which let water in.
Read more: Curious Kids: how do bushfires start? Sitting in front of a fire watching the flames and listening to the wood crackle and pop can be fun. Most of the time the mini explosions of the steam escaping are small.
But sometimes they can be big, and might even cause small chunks of burning wood to fly out of the fire! The author thanks her nephews Aldous Nolan 6 and Fergus Nolan 5 for helping to improve this answer. Hello, curious kids! Have you had your annual chimney inspection? Our professional chimney sweeps can help to ensure that you can safely burn whichever type of firewood you prefer.
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