Fire: What a Tree Gives Back
The expanded guide to the Fire episode: the gap between the log and the flame, why an ember brightens when you blow on it, and the surprise that most of a log arrived out of the air. Choose the age that fits your listener.
For ages 4–6
The big idea
Look closely at a candle or a campfire and you will see something strange: the flame does not quite touch the thing that is burning. There is a tiny gap underneath it. The flame is floating.
That is because the wood is not what is burning. When wood gets hot, invisible gases come out of it, and those gases are what catch fire, floating just above. The orange colour is tiny specks of soot, so hot that they shine.
And here is the biggest surprise. A tree builds itself mostly out of the air, using sunlight to do it. So when a log burns, most of it is going back into the air it came from. A fire is old sunlight, coming back out.
Wonder together
- Why do you think the flame floats instead of sitting right on the wood?
- If a tree is mostly made of air, where did the rest of it come from?
- What does a fire give us, and what does it give back?
- Why do you think fire is orange and not blue or green?
- If you could ask a tree one question, what would it be?
Let's try it
The Flame That Floats
You'll need
- A candle in a steady holder
- A grown-up to light it and stay with it
- A dark-ish room so the flame shows up
What to do
- Ask your grown-up to light the candle and set it somewhere safe, then sit back a little way.
- Look at the very bottom of the flame, right where it meets the wick. Find the small dark gap.
- That gap is the gas coming off the wick before it catches. The flame is burning the gas, not the wick.
- When you are finished, ask your grown-up to blow it out, and watch the thin ribbon of smoke go up. That smoke is the gas, escaping without burning this time.
Science words
- Flame
- The bright part of a fire. It is gas burning in the air, not the wood itself.
- Ember
- A glowing orange lump left when the flames have gone. It is still burning, just quietly.
- Soot
- Tiny black specks inside a flame. When they get hot they shine, and that is the orange you see.
- Ash
- The soft grey powder left at the end. It is the part of the wood that came from the ground.
- Oxygen
- Part of the air. Fire needs it, which is why blowing on an ember makes it brighter.
Spot it in real life
- Next time you see any flame, look for the dark gap at the bottom. It is always there.
- Watch a candle being blown out and follow the smoke ribbon upward.
- Look at a used barbecue or fireplace and find the three stages: black charcoal, grey ash, white ash.
- Notice how a fire gets brighter when the wind picks up, and quieter when it drops.
Read this one aloud, slowly
Think about a campfire at the end of a long evening. The big flames are gone now. What is left is a low pile of embers, glowing soft and orange in the dark, warm without any hurry at all. All that warmth came from the sun. A tree stood out in the light for years and years, gathering it up a little at a time, holding it in its wood. And tonight it is letting it go again, slowly, quietly, giving it all back. Nothing is lost there. It is only going home. You can let the day go the same way. Breathe out slow and warm, like an ember, and let it all settle down to quiet.
For ages 7–10
The big idea
There is a gap between a log and the bottom of its flame, and it is there for a reason. Heat does not burn wood directly. It drives flammable gases out of the wood first, and those gases burn in the air just above it. The flame is floating because it is burning something the log is giving off.
The orange is not the colour of burning. It is incandescence: specks of soot caught in the flame, heated until they glow, the same way a hot wire in a toaster glows. Blowing on an ember delivers more oxygen, so it burns faster and hotter and the glow brightens.
And then the part worth sitting with. A tree builds its wood mostly from carbon dioxide taken out of the air, assembled with energy from sunlight. So a dry log is, in large part, air and old sunlight made solid. When it burns, most of that carbon goes straight back to the air. The ash left behind is the small part that really did come from the ground.
Wonder together
- Why is there a dark gap between the log and the bottom of the flame?
- A tree is enormous and the air feels like nothing. How can most of a tree have come out of it?
- Blowing makes an ember glow brighter but puts a candle out. What is different about the two?
- If burning returns the carbon to the air, where was that carbon the day before the tree took it?
- Charcoal, grey ash, white ash. What do you think is being lost at each stage?
Let's try it
Put a Fire Out Without Water
You'll need
- A candle in a steady holder, on a heatproof surface
- Two clear glass jars of clearly different sizes
- A stopwatch or phone timer, and a grown-up for every step involving the flame
What to do
- Your grown-up lights the candle. Everyone else stands back and takes a job: one on the timer, one to call out what they see.
- The grown-up lowers the smaller jar over the candle, upside down and right to the surface. Start the timer the moment it seals.
- Watch the flame carefully as it goes. It will shrink and change colour before it goes out. Stop the timer and write down the seconds.
- Let the air clear, relight, and do the whole thing again with the larger jar. Compare the two times.
Science words
- Pyrolysis
- Heat breaking a solid down into gases before anything burns. It is what makes the gap under the flame.
- Combustion
- Fuel combining with oxygen and releasing energy as heat and light.
- Incandescence
- Giving off light because of being hot. The orange of a flame is glowing soot, not a chemical colour.
- Charcoal
- What is left when the gases have been driven out of wood but the carbon has not burned yet.
- Ash
- The minerals that cannot burn. This is the part of the wood that genuinely did come from the soil.
- Carbon cycle
- The round trip of carbon between air, living things and the ground. A fire is one fast leg of it.
Spot it in real life
- Find the dark gap under any flame, then look at a gas hob where the gas is already a gas and the gap is almost gone.
- Watch a toaster element go from dark to orange. That is incandescence, the same effect as the soot in a flame.
- Look at a barbecue the morning after and sort what is left: black charcoal, grey ash, white ash.
- Weigh a dry log, then imagine that most of that weight arrived through leaves, as gas.
Printable
The Bedtime Scientist · Track & write
Follow the Carbon Round
Challenge: Complete the loop: draw the arrows that are missing and label each stage. Start at the sun, go to the tree, into the wood, into the fire, and back to the air. Then mark the one place where something leaves the loop and stays behind, and name it. Finally, in a sentence: a log feels heavy and air feels like nothing, so how can most of the log have arrived as gas?
Journal: A tree spends years quietly taking something in, and a fire gives most of it back in an evening. Write about something you have been slowly gathering, and what it would look like to let some of it go.
Calm science for curious minds, ages 4–104.
Read this one aloud, slowly
Picture the fire late on, when the flames have gone and only the embers are left, glowing low and orange and giving off a steady, unhurried warmth. Every bit of that warmth is sunlight that arrived years ago. A tree stood out in the open and gathered it, a little each day, pulling carbon out of the air and building itself out of light and gas, and holding all of it in its wood for as long as it stood. Tonight it is letting go of it again. The heat on your face is that sunlight, released. The smoke going up is most of the tree, heading back to the air it was made from. Nothing is being destroyed out there. It is a long loan, being quietly paid back. Let your own breathing slow to the pace of the embers, out and warm and unhurried, and let the day hand itself back too.
A Silly Science Story
What the Tree Was Holding
Pick the silliest words you can. The story stays true no matter what you choose: that's the science hiding inside the giggles. Fill in the blanks and watch it come alive.
A long time ago, in a wood full of an animals, there stood a a describing word tree. Every single day for a big number years, that tree did the same quiet thing: it opened its leaves to the sunlight and pulled in the invisible air around it, and out of nothing but light and gas it slowly built more of itself. Nobody saw it happening. It made no a sound at all. Then one autumn a branch came down, and a name found it and carried it home for the fire. That night the branch got hot, and gases came creeping out of it and caught alight just above the wood, which is why the flame seemed to a silly action (ends in -ing) rather than sit down properly. The whole room went warm. And every bit of that warmth was sunlight the tree had been keeping safe, handed back at last. In the morning all that was left was a little grey powder, about as much as a spoonful of a food. That part, and only that part, had come from the ground.
Word bank, to fill in by hand:
- an animal
- a describing word
- a big number
- a sound
- a name
- a silly action (ends in -ing)
- a food
Make it a Family Science Night
Tonight's experiment is even better shared. Turn it into a small event, nothing you don't already have, no pressure, just one other family and a calm hour.
The plan
- Pick a night and invite one other family. Send a text, or hand a child the placemat below to deliver.
- Set out the few things the experiment needs.
- Start the episode together, then try the experiment while it's fresh.
- Let the kids lead. Grown-ups just wonder out loud alongside them.
- End calm: dim the lights and read the bedtime tie-back aloud to everyone.
Scan to listenFamily Science Night
Tonight we're exploring
where a flame comes from, and where it all goes afterwards.
Scan the code to listen together, then try tonight's experiment.
The grown-up's 60 seconds
This episode came from five questions a seven-year-old asked after a campfire, and it is worth knowing where it ends up, because the answer is genuinely startling the first time you meet it. A tree does not build itself out of the ground. It builds itself mostly out of the air: carbon dioxide pulled in through its leaves, assembled using energy from sunlight, with water from the soil and a small mineral contribution that eventually becomes the ash. So a dry log is, in large part, air and old sunlight in solid form. Burning it undoes that, releasing the stored energy as heat and light and returning most of the carbon to the atmosphere. The flame you are watching is not the wood. Heat drives flammable gases out of the wood, and those gases burn just above it, which is why there is a dark gap between the log and the bottom of the flame, and why a flame appears to float. For a grown-up sitting beside a fire, there is something steadying in it: nothing is being destroyed, only handed back.
Two small things, if you have a minute
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I like your mind. Just the way it wonders.