The Imposter
Two glasses. Same water. Same egg. Drop it in the first — it sinks. Drop it in the second — it floats. The glasses look identical. One of them is lying.
5-12 yrs
Easy
15
min
Stage 1-3
Mission Briefing.
Designed by Darin Carr (BSc, DipEd)
NESA Accredited Teacher Chemistry & Physics Specialist
Creator of the LAB™ Learning System
Mackey
>
The Imposter
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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
2 tall clear glasses
Water
Salt — you'll need a lot
A spoon or stirrer
1 raw egg
Let’s Investigate
1
Set up the glasses
Fill both tall glasses with the same amount of water — about three-quarters full. T
hey must look identical.
Place them side by side. This is your line-up. One is about to become the imposter.
3
Make your prediction
Before the egg goes anywhere: look at both glasses.
They look identical.
You're about to drop the same egg into each one. What do you think will happen — same result in both?
5
Push it under
With the egg floating in the salt water, use your finger to push it gently below the surface and release it.
What happens?
Try the same thing in the plain water — push the sunken egg down further, then let go.
What happens there?
2
Make the Imposter
Into one glass only, add 6 to 8 tablespoons of salt.
Stir vigorously until it has completely dissolved and the water looks clear again.
The imposter is ready — and it looks exactly like the innocent glass next to it.
4
Test the Egg
Gently lower the egg into the plain water glass first.
Watch what happens.
Then carefully lift it out, dry it gently, and lower it into the salt water glass. Watch what happens.
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.
A ship made of steel weighs thousands of tonnes — and floats. A small pebble weighs almost nothing — and sinks. Floating isn't about how heavy something is.
Here's your prediction before you touch anything: you have two glasses of water and one raw egg. You're going to drop the egg into each glass. What do you think will happen — and if the result is different each time, what could possibly explain it? The glasses look identical.
Write it down. You're about to catch an imposter.
Test the egg in the plain water first — watch it sink, then try pushing it down and letting go
Now test the egg in the salt water — notice how high it sits, and try pushing it under and releasing
Both glasses of water look the same from the outside. What is actually different about them — and why does that change what the egg does?
When you pushed the egg down in the salt water and let go, what happened? What does that tell you about the force the water is pushing back with?
The more salt you dissolve, the higher the egg floats. What do you think you're actually changing about the water when you add salt?
Salt dissolved in water adds mass without adding much volume — making the water denser. Denser water pushes back harder. When it pushes harder than the egg weighs, the egg floats.
👉 The Dead Sea has so much dissolved salt that people float on the surface without swimming — what does that tell you about how much salt changes water's density?
Where else in everyday life does density determine whether something sinks, floats — or hovers in between?
"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 amount of salt change how high the egg floats — is there a minimum amount needed before it floats at all?
Does the size of the egg change how much salt you need — does a larger egg need denser water to float?
🧪 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
Same egg. Same glass. One sinks. One floats. Nothing about the egg changed — but the water is keeping a secret.
Floating is about density — how much mass is packed into a given space. A raw egg is slightly denser than fresh water, so when you drop it in, the water can't push back hard enough to support it. It sinks.
Dissolve salt into the water and something quiet happens. You're adding mass without adding much volume — the water gets heavier without getting much bigger. Its density creeps upward. And as density increases, so does the force the water pushes back with — what scientists call buoyancy.
Add enough salt and the water becomes denser than the egg. Now the push-back force is greater than the egg's weight — and up it goes. The egg didn't change. You changed the rules.
Did you notice the egg seems to float at a very specific level rather than just bobbing on top? It's finding its exact density match — the point where the push-back force equals its weight precisely. Move it higher and it sinks back. Push it lower and it rises again.
You can see the same average density principle doing something even more counterintuitive with an orange in [The Life Jacket], and watch salt change a potato's fate entirely in [Sink or Float?].
What would happen if you made a glass of very salty water and carefully poured fresh water on top — could you get the egg to float perfectly in the middle, suspended between two layers?
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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