Drink Up
Light a candle on a plate of water, lower a glass over the top — and watch the glass drink the water right off the plate. No pumps. No suction. Just a flame, some air, and a force you can't see.
7-12 yrs
Easy
5
min
Stage 3
Mission Briefing.
Designed by Darin Carr (BSc, DipEd)
NESA Accredited Teacher Chemistry & Physics Specialist
Creator of the LAB™ Learning System
Essy
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Drink Up
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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
A shallow plate or wide dish
Water
A birthday candle or small tea light
Blu-tack or a small lump of modelling clay
A clear drinking glass or tall jar
Food colouring
Matches (adult use only)
Let’s Investigate
1
Set up the plate
Pour water into your shallow plate — about 1 to 2 cm deep. Add a few drops of food colouring and stir gently.
Press your birthday candle into a small lump of blu-tack and stand it upright in the centre of the plate.
3
Light the candle
An adult lights the candle and lets it burn for 10 to 15 seconds — long enough to heat the air inside the glass before it goes on.
5
Watch Carefully
The flame goes out. Watch closely — how high does it climb? Is the speed surprising? Count how many seconds from flame-out to the water stopping.
2
Make your prediction
Before you light the candle: look at the plate of water, the candle, and the glass.
Write down exactly what you think will happen to the water level inside the glass when the flame goes out. Up? Down? Stay the same? By how much?
4
Lower the glass
Carefully lower the clear glass straight down over the burning candle until the rim sits flat on the plate, sealing in the flame.
Watch for tiny bubbles escaping out the bottom as the glass comes down — that's hot air being pushed out.
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 already know fire needs air to burn. Leave a candle burning in a closed space long enough — and it goes out.
Here's your prediction before you touch anything: if you lower a glass over a lit candle sitting in a plate of water, and the flame goes out — what do you think will happen to the water?
Write it down. Up? Down? Nothing? There's a reason this experiment has surprised people for hundreds of years.
Watch the moment the glass touches the plate — look for tiny bubbles escaping out the bottom before the seal forms
Focus on the water inside the glass as the flame goes out — how fast does it move?
Most people think the flame "uses up the oxygen" and that pulls the water in. But the water starts rising almost instantly when the flame goes out — does that match an explanation about oxygen running out slowly?
You can see bubbles leaving the glass just before it seals. Where did that air go — and what filled the space?
What do you think would happen if you used a taller glass — would more water rise, less, or the same amount?
When the air inside cools, it contracts and pulls back — creating lower pressure than the air outside, which pushes the water up to fill the gap.
A suction cup on a smooth wall holds by the same principle — how is sticking a suction cup to a window the same idea as what just happened inside your glass?
When you squeeze a dropper, release it underwater, and it draws liquid in — which part of this experiment does that remind you of?
Weather systems work the same way — low pressure pulls air in, high pressure pushes it out. Which one would your glass be, right after the flame goes out?
Where else in everyday life is invisible air pressure doing the heavy lifting — without you ever noticing?
"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 height of the glass change how much water rises — does a taller glass produce a bigger effect?
Does using more candles change how high the water rises, or how quickly it happens?
🧪 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
Here's what almost every website gets wrong about this experiment: it's not about oxygen.
The popular explanation says the flame burns up the oxygen inside the glass, and that's what pulls the water in. It's a tidy story. It's also incorrect — and you can prove it yourself just by watching: the water starts rising almost the instant the flame goes out.
What's actually happening is air pressure — the same invisible force that powered [Feed the Monster].
When you lower the glass over the candle, the flame heats the air trapped inside. Hot air expands — the molecules speed up and spread out, pushing harder against everything around them. You can actually see some of that hot air escape as tiny bubbles from under the rim of the glass before it seals against the water.
The moment the flame goes out, that hot air starts cooling rapidly. Cooling air contracts — the molecules slow down and huddle closer, taking up less space and pushing outward with less force. The pressure inside the glass drops.
The air outside the glass is still at full atmospheric pressure — the weight of the entire column of air above you pressing down. That outside pressure pushes down on the water around the glass and up into the lower-pressure space inside. The water rises until the pressures equalise.
The taller the glass, the more air there is to cool and contract, and the more the pressure difference can develop — which is why taller glasses tend to produce more dramatic results.
That same outside pressure holds an entire cup of water in place with nothing but a card in [The Magic Water Cup] — same force, completely different trick.
Curiosity spark: What do you think would happen if you warmed the glass first by holding it in your hands before the experiment — would that change how much water rises?
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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