Coke Density
Designed by Darin Carr (BSc, DipEd)
NESA Accredited Teacher Chemistry & Physics Specialist
Creator of the LAB™ Learning System
This simple experiment reveals a hidden secret inside everyday drinks.
Even though the cans look almost identical, something inside them changes how they behave in water.
Drop them in and watch closely…
you’re about to uncover a surprising science trick hiding in plain sight.
7-12 yrs
Easy
15
min
Stage 1-3
>
Coke Density
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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.
What you will need
1 can of regular Coke
1 can of Diet Coke (or any diet soft drink)
Large clear container or tub
Water
How to do it
1
Fill Your Container
Fill a large container with water deep enough to fully submerge both cans.
3
Test the Diet Coke
Now carefully place the Diet Coke into the water.
2
Test the Regular Coke
Gently place the regular Coke into the water and observe what happens.
4
Compare the Results
Watch closely:
One sinks
One floats
Same size… completely different behaviour!
Did it work? Share the science! Tag @the_crazy_scientist on Instagram — we love seeing your experiments!
The Crazy Scientist Lab System™
Every experiment follows The Crazy Scientist Lab 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.
Why do some objects float and others sink?
Do heavier things always sink?
Can two things that look the same behave differently?
Watch carefully as each can is placed in the water
Compare what happens — don’t rush!
Look for differences between the two cans
Something hidden inside is affecting the result…
This same idea — that what's packed inside something determines whether it floats or sinks — is why a massive steel ship floats (it's mostly hollow, so its average density is low) but a solid steel ball sinks.
It's also how submarines choose their depth: they pump water in or out of ballast tanks to change their average density.
Think about that: the submarine doesn't change its size or shape — just what's inside it.
What else around you might float or sink differently if you changed what was packed inside?
"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.
What happens if you try different brands of soft drink?
What happens if you use sugar-free vs full-sugar drinks?
🧪 Try it! Change ONE thing and test again. What did you discover?
The Science Behind It
Same size cans. Same amount of liquid. One sinks. One floats. How is that even possible?
It all comes down to density — how much stuff is packed into a space. Both cans take up exactly the same amount of room, but what's inside them is very different.
Regular Coke is loaded with sugar — around 39 grams per can. All that sugar dissolves into the liquid and makes it heavier than water. So it sinks.
Diet Coke uses artificial sweeteners instead, and here's the wild part — those sweeteners are so incredibly powerful that you only need a tiny pinch to get the same sweetness. Barely anything extra dissolved in the water. Barely any extra weight. So it floats.
Did you notice both cans feel almost identical when you hold them? Your hands can't feel the difference — but the water can. Water always knows exactly how dense something is, and it never gets it wrong.
That's Archimedes' principle — if something is denser than water, it sinks. Less dense? It floats. Simple as that. Except... it's really not that simple at all.
Because here's the question — how does a massive steel ship float when a tiny steel coin sinks straight to the bottom? Find out in The Crazy Scientist Lab!
Know a parent or teacher who'd love this? Send it on! 👇
The Crazy Scientist books
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Designed by a practising NSW classroom teacher (30+ years experience), these books directly support NSW Science & Technology (2024) outcomes and reinforce “Working Scientifically” skills.
Perfect for classroom libraries or home explorations.
For teachers (YouTube)
— Science Before the Bell
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The Crazy Scientist Lab - Want to teach this like a real scientist?
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🔒Differentiation guide 🔒Full instructional video 🔒Extension activities
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