The Coin Heist
Mackey
Mission Briefing.
A piece of card sits on top of a glass. A coin sits on top of the card. Your mission: get the coin into the glass — without touching it. You have one move. Make your prediction before you try.
5-12 yrs
10
min
Easy
Stage 1-3
Designed by Darin Carr (BSc, DipEd)
NESA Accredited Teacher · Chemistry & Physics Specialist · 30+ years in-class teaching
Creator of the LAB™ Learning System
Last updated: June 2026 ·
[Cite this resource ↗]
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The Coin Heist
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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 glass or cup
1 piece of stiff card
A small collection of coins — 5c, 10c, 20c, 50c, $1, $2 Australian coins work perfectly
A flat, stable surface — a table or desk
Let’s Investigate
1
Set up the heist
Place your glass on a flat, stable surface.
Lay the piece of card across the top of the glass so it covers the opening completely and rests on the rim on both sides.
Balance one coin in the centre of the card, directly above the opening of the glass.
3
Pull off the heist
Position your finger at the edge of the card, close to the glass rim.
Flick the card with a sharp, fast, horizontal movement — like you are trying to snap it off the glass in one clean motion.
5
Mass test
Test the same experiment with different coins.
Try a 5c coin, then a $2 coin.
Which is easier to get into the glass — the lighter coin or the heavier one?
2
Make your prediction
Here is the plan: flick the card sharply and horizontally off the glass — so the card shoots away but the coin is left behind.
Before you try it, write down your prediction.
Will the coin:
a) fly off sideways with the card,
b) stay in the air for a moment then fall into the glass, or
c) drop straight into the glass the instant the card moves?
4
Stack the coins
Reset the card on the glass.
This time, stack two coins in the centre.
Predict: will two coins be easier, harder, or the same as one? Flick the card again. Now try three coins four etc
6
Slow flick test
Reset with one coin on the card.
This time, instead of a fast flick, slide the card slowly and steadily off the glass.
What happens to the coin this time — and how is that different from the fast flick?
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.
Have you ever been in a car that stopped suddenly — and felt your body lurch forward? Or slid forward on your seat on a bus when the brakes came on?
That feeling is your body trying to keep moving even though the vehicle has stopped. Your body wants to stay doing whatever it was already doing.
Objects are the same. Sitting still? Want to keep sitting still. Moving? Want to keep moving. They resist any change.
There is a coin sitting on a card, sitting on a glass. The coin is at rest. It wants to stay exactly where it is.
Predict: if you flick the card away very quickly, what will the coin do?
The card flew away — but the coin dropped straight into the glass. Think about the moment the card was moving: was the coin moving with it, or not?
When you tried the slow flick, the coin moved with the card instead of dropping in. What was different about the slow flick — and what does that tell you about what the coin was responding to?
The card had to push the coin to move it. In the fast flick, that push lasted a very short time. Was that enough time to get the coin moving? What does that tell you about how inertia works?
When you stacked more coins, the heist still worked. Did more mass make it easier or harder — and does that match what you predicted?
Newton's First Law says every object resists any change to its motion. The coin resisted moving sideways. The slow flick was long enough to overcome that resistance. The fast flick wasn't.
When a car crashes into a wall and stops instantly, the passengers keep moving forward. A seatbelt applies a force to stop them — but what would happen without one? How is this the same physics as the coin heist?
"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 mass of the coin affect whether the heist works — is a heavier coin easier or harder to get into the glass than a lighter one?
Does the type of card affect the result — does a smoother card (like a playing card) work differently from a rougher card (like corrugated cardboard)?
🧪 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
Why did the coin stay still while the card flew away?
The coin has inertia — the tendency of any object to resist a change in its motion. The coin was at rest. It wanted to stay at rest.
When you flick the card, the only thing that could move the coin sideways is friction — the tiny gripping force between card and coin. In a fast flick, the card is gone in a fraction of a second.
That’s not enough time for friction to transfer enough force to get the coin moving. The coin never receives the message that the card has left — it stays exactly where it was.
With nothing beneath it, gravity pulls the coin straight down into the glass.
Why speed is everything?
In the slow flick, friction has much longer to act. The force builds up over time, the coin starts sliding with the card, and the heist fails.
In the fast flick, the contact time is so short that friction can’t do its job. Speed is what separates success from failure — not strength.
This is why the magician’s tablecloth trick works: the cloth is pulled so fast that friction barely has time to act on the plates and glasses sitting on top.
Why more mass actually helps?
You might expect a heavier coin to be harder to leave behind — but heavier objects have more inertia. More inertia means more resistance to any change in motion.
A heavier coin grips its stillness even harder. The $2 coin isn’t harder to heist — if anything, it cooperates better than the 5c coin.
Mass is not the enemy of inertia. Mass is inertia.
Real-world connection
A seatbelt, a crash helmet, and the restraints astronauts wear at launch all exist for the same reason: to change an object’s motion, you need a force — and that force needs time.
When a car stops suddenly, your body keeps moving forward. The seatbelt applies force over time to stop you. Without it, nothing does.
Try next
• See inertia working against motion rather than in favour of stillness → [The Gravity Battlefield]
• Another experiment where a fast force does something a slow force cannot → [The Impossible Blow].
Teachers & Homeschoolers: Print-ready HD versions of this Science Behind It poster and companion G&T Challenge Card are available inside The Crazy Scientist LAB.
Extension: G&T Years 5 & 6
What is inertia, really?
Inertia isn’t a force — it’s a property of matter. It describes how strongly an object resists any change to its motion.
The more mass an object has, the more inertia it has. That’s why a heavy coin is not harder to leave behind — it actually resists sideways motion even more strongly than a light one.
Newton’s First Law Around 1687
Isaac Newton described the principle that governs this experiment:
An object will remain at rest or continue moving in a straight line at constant speed unless acted on by an unbalanced force.
The coin is at rest. The only sideways force available is friction — and in a fast flick, friction acts for such a short time that it cannot change the coin’s motion.
Teachers & Homeschoolers: Print-ready HD versions of this Science Behind It poster and companion G&T Challenge Card are available inside The Crazy Scientist LAB.
Vocabulary
Inertia: The tendency of an object to resist any change in its motion. A coin at rest wants to stay at rest.
Friction: A force between two surfaces that resists motion. In a fast flick, friction acts too briefly to move the coin.
Newton’s First Law: A rule of motion: objects stay at rest or keep moving unless a force changes their motion.
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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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