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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.
From the LAB
What you will need
2 rolling chairs (office or classroom chairs with wheels)
2 scooter boards
2 skateboards (works perfectly if available)Q
How to do it
1
Set Up
Place two rolling chairs (or boards or skateboards) facing each other on a smooth floor, approximately 2 metres apart.
One participant sits on each.
Stretch the rope between them so each person holds one end with both hands
3
Run the experiment
Nominate one participant as the puller.
The puller grabs their end of the rope and, on your signal, pulls steadily toward themselves.
The holder simply holds their end firmly — they do not pull, they do not push.
2
The prediction
Before anything happens, predict if one person pulls - who moves? (one: which one and /or both)
Did it work? Share the science! Tag @the_crazy_scientist on Instagram — we love seeing your experiments!
Newton's Question: Who Moves?
Designed by Darin Carr (BSc, DipEd)
NESA Accredited Teacher Chemistry & Physics Specialist
Creator of the LAB™ Learning System
One person grabs the rope and pulls. Nobody pushes. Three things could happen — and almost every audience picks the wrong one. Newton figured out why in 1687. Your students are about to discover it for themselves.
7-12 yrs
Easy
15
min
Stage 2, Stage 3
>
Newton's Question: Who Moves?
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.
In a tug of war — which team is pulling harder? The winning team, right?
Newton said no. Both teams pull the rope with exactly the same force. Every moment of the match.
If that's true — what actually wins a tug of war?
Today's experiment will show you. But first — predict:
Option A: The puller moves toward the holder. The holder stays still.
Option B: The holder moves toward the puller. The puller stays still.
Option C: Both move toward each other.
Write down your option and your reason.
You just watched both people slide toward each other — every time, no matter who pulled.
Think back to the exact moment the pull happened. Describe what you saw for each person — direction, speed, distance.
The holder never pulled anything. They just held on. Something moved them anyway.
What force acted on the holder — and where did it come from, if the holder didn't create it?
The lighter person travelled further, even though both people felt the same rope force. What is the variable that controlled how far each person moved?
You cannot push or pull something without it pushing or pulling back — equally, in the opposite direction.
That is Newton's Third Law. Forces always come in pairs. The puller and the holder are always a pair.
A rocket pushes exhaust gases backward at enormous speed. What pushes the rocket forward — and where does that force come from?
"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 it make a difference if the two participants are very different sizes?
What happens if you run the experiment on carpet instead of a smooth floor?
🧪 Try it! Change ONE thing and test again. What did you discover?
Want to go deeper? Tap a section below to explore. ▼
The Science Behind It
Newton's Third Law of Motion states: for every force, there is an equal and opposite reaction force. Forces never exist alone — they always come in pairs, acting on two different objects, pointing in opposite directions.
When the puller grabs the rope and pulls it toward themselves, they apply a force on the rope — and through the rope, on the holder. At the exact same moment, Newton's Third Law produces a reaction: the rope pulls back on the puller with an equal force in the opposite direction. Two forces, same size, opposite directions, two different objects.
Both people are sitting on low-friction rolling surfaces with almost nothing to resist those forces. So both people move — toward each other — every single time.
The reason this surprises most people is a common misconception: we tend to think that only the person doing the acting (the puller) creates a force, and the other person (the holder) just receives it passively. Newton's Third Law says this is wrong. The holder's hands pull back on the rope just as hard as the puller's hands pull forward. There is no such thing as a one-way force.
When participants of different mass are paired (Step 4), both still feel the same force from the rope — but the lighter person accelerates more. This is Newton's Second Law: force equals mass times acceleration (F = ma). Equal force, less mass, greater acceleration. The lighter person travels further in the same amount of time.
Friction is the only thing that can prevent this result. If the floor grips the chair strongly enough, the friction force from the floor cancels out the rope force and the chair does not move. This is why smooth floors produce the clearest results — and why tug of war is won by friction against the ground, not by pulling the rope harder.
To see the same Third Law force pairs at work without any rope at all — just escaping gas and a flying object — see [Balloon Rocket Blast-Off]. To see friction doing the opposite job — not preventing motion, but actively reversing it — see [The Disobedient Hoop].
Extension: G&T Years 5 & 6
Vocabulary
Know a parent or teacher who'd love this? Send it on! 👇
The Crazy Scientist books
These highly visual books combine storytelling and real science, helping students revisit key concepts and stay engaged long after the session.
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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Quick, curriculum-linked science you can teach tomorro
Try Another Crazy Experiment
Keep the science going with these fun experiments
Let's Go!
Keep exploring with The Crazy Scientist
Hands-On Science Workshops
Interactive STEM experiences aligned to the NSW syllabus.
