Feed the Monster
Stick googly eyes on a glass bottle, fill a water balloon just too big to fit inside — and watch the monster eat it anyway. No pushing. No squeezing. Just science.
7-12 yrs
Medium
10
min
Stage 3
Mission Briefing.
Designed by Darin Carr (BSc, DipEd)
NESA Accredited Teacher Chemistry & Physics Specialist
Creator of the LAB™ Learning System
Professor Picklebottom
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Feed the Monster
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NESA Accredited Teacher
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High school chemistry & physics specialist 30+ years
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The Crazy Scientist in primary schools — 15 years
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International conference presenter on science education
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Creator of the LAB™ Learning System
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Curriculum aligned: NSW Science & Technology K–6 (2024)
A picture is worth a thousand words — check this out and see if you can spot the science hiding in plain sight.
Mission Equipment
1 clear glass bottle — 400ml milk-bottle style works perfectly
Water balloons
Water
Matches — adult use only
Googly eyes (or a permanent marker to draw eyes and a mouth)
A thin straw
Let’s Investigate
1
Build your monster
Stick two googly eyes near the top of your glass bottle.
If you don't have googly eyes, draw them on with permanent marker — add a big open mouth around the bottle's opening while you're at it. Your monster is ready. And it's hungry.
3
First Try
Before lighting anything — try to push the balloon into the bottle with your hand. Really push.
What happens?
5
Feed the Monster
While the match is still burning — or immediately after it goes out — quickly place the water balloon over the mouth of the bottle.
Hold it gently in place and watch. The monster is eating.
7
Try it again
Now run it again — but change just one thing.
2
Make the meal
Fill a water balloon with water until it's slightly larger than the bottle's opening — about 5 to 6 cm across. Tie it off.
Sit it on top of the bottle's mouth to test: it should rest ON TOP without falling in. That's your monster's meal.
4
Light the match
An adult lights a match — or 3 to 4 matches at once for a bigger effect — and drops them into the bottle.
Watch the flame through the glass as it heats the air inside the monster's belly.
6
Spit it out
To get the balloon back out, slide a thin straw down alongside the balloon into the bottle and blow gently.
Air flows in, pressure equalises inside and outside — and the balloon pops back out. The monster spits out its meal, ready to eat again.
Did it work? Share the science! Tag @the_crazy_scientist on Instagram — we love seeing your experiments!
The Crazy Scientist LAB Learning System™
Every experiment follows The Crazy Scientist Lab Learning System™ — a simple way to help kids think like real scientists.
We
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LINK to what they already know,
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ACTIVATE curiosity through hands-on discovery
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BUILD understanding that actually sticks.
You know air is everywhere — but you probably don't think of it as something that can push.
Here's your prediction before you light anything: if you fill a water balloon just slightly too big to fit into the bottle's mouth, and you can't push it in with your hands — what do you think COULD get it in?
Write down your idea. Then build your monster — and let it get hungry.
Why couldn't you push the balloon in with your hands, but the monster ate it anyway?
What do you think changed inside the bottle between the match burning and the balloon going in?
When you blew through the straw and the balloon came back out — what does that tell you about what was holding it in?
When air cools, it contracts and takes up less space — dropping the pressure inside the bottle below the pressure outside. The outside air pushes the balloon in to equalise.
A vacuum sealer removes air from a bag to preserve food — how is that the same idea as your hungry monster?
When you open a jar of pasta sauce and it makes a "pop", you're breaking a pressure seal — what created that seal in the first place?
Aeroplanes are pressurised inside — what do you think would happen to the cabin if a window cracked at 10,000 metres?
Where else in everyday life is invisible air pressure doing something you've never noticed?
"Want the full teacher guide? The Crazy Scientist Lab includes classroom delivery tips, how to manage the WOW moment, differentiation for Stage 2 & 3, — ready to teach tomorrow."
Think Like a Scientist
Scientists don't just do ONE experiment; they change one part of the experiment (independent variable) and then see how it affects another part of the experiment
(dependent variable)
Change ONE variable and test again.
Does the number of matches change how far the balloon gets pulled into the bottle — or how quickly it happens?
Does the size of the water balloon change how completely the monster eats it?
🧪 Try it! Change ONE thing and test again. What did you discover?
Dr Puddledrip’s Science Tip
Want to go deeper? Tap a section below to explore. ▼
The Science Behind It
Your monster is powered by air pressure — and air pressure is surprisingly strong.
Here's what's actually happening inside the bottle.
When the match burns, it heats the air inside. Hot air expands — the molecules speed up and spread out, pushing harder against everything around them. Some of that hot air actually escapes out the top before you place the balloon.
The moment you place the balloon over the mouth, you seal the bottle. The fire goes out — it runs out of oxygen and the heat disappears. The air inside starts to cool rapidly.
Here's the key: cooling air contracts. The molecules slow down and huddle closer together, taking up less space and pushing outward with less force. The pressure inside the bottle drops.
But the air outside the bottle hasn't changed at all. It's still at full atmospheric pressure — the weight of the entire column of air above you pressing down. That outside pressure is now much greater than the pressure inside.
So the outside air pushes the balloon inward, trying to equalise the two pressures. And it's strong enough to pull the balloon right past the rubber's resistance and into the bottle.
That same outside pressure is doing something equally impossible-looking in [The Magic Water Cup] — where it holds an entire cup of water in place with nothing but a card — and something just as surprising in [The Chatterbox Tube], where a single breath inflates an entire tube by letting the atmosphere do the work.
Curiosity spark: What do you think would happen if you used a bottle that had been sitting in the sun and was already warm inside — would the monster eat faster, slower, or not at all?
Find out in The Crazy Scientist Lab.
Extension: G&T Years 5 & 6
Vocabulary
Know a parent or teacher who'd love this? Send it on! 👇
READY TO TEACH THIS
TOMORROW?
Running the experiment is easy; however, teaching it well is another challenge.
Teachers often ask:
How do I adapt this for Stages 1,2 or 3?
What do I do with fast finishers?
What misconceptions will they have?
How do I structure this for a full class?
What syllabus outcomes does it cover?
What do I say when they ask WHY?
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