The Disobedient Hoop
The Disobedient Hoop science experiment for kids — a green hula hoop rolling across a wooden floor demonstrating backspin and friction. The Disobedient Hoop experiment by The Crazy Scientist.
7-12 yrs
Easy
10
min
Stage 2, Stage 3
Mission Briefing.
Designed by Darin Carr (BSc, DipEd)
NESA Accredited Teacher Chemistry & Physics Specialist
Creator of the LAB™ Learning System
Alex
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The Disobedient Hoop
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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 smooth, flat floor — tiles or floorboards work best
Open space of at least 5 metres in front of you
Optional: chalk or tape to mark the starting position and measure return distance
Let’s Investigate
1
The prediction
What happens if the hoop is released forward, but the hoop is spun backward at the same time?
2
The Spin & release
Pick up the hoop and prepare to throw it forward — as you release it, flick your wrist to spin the hoop backwards (in the opposite direction to its travel).
The throw goes forward. The spin goes backward. Release and step back.
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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.
Skid a ball across a floor — it slows down. Slide a book across a table — it stops. Friction slows things. That is what friction does. That is ALL friction does.
Right?
What if friction could do the opposite — take something moving forward and send it rolling the other way?
Predict: can friction reverse a direction of travel? And if it can — what would that look like?
Write it down. Then watch.
You just watched a hoop travel forward — then reverse direction — with nothing visibly pushing it back.
Think back to the exact moment it changed direction. Describe what you saw: fast or slow? Did it stop first, or turn smoothly?
What was the only thing different between the first throw and the second?
Nothing hit the hoop to reverse it. Something at the contact point with the floor did. What was happening there — and in which direction was that force acting?
The hoop slowed before it reversed. If friction only slowed it, it would have stopped. Something else pushed it backward. Where did that backward push come from?
Friction usually slows things down. Here, friction reversed an entire direction of travel.
The spin and the throw were fighting each other at the contact point — and friction decided the winner.
If you ran this experiment on ice instead of a wooden floor, would the hoop still come back? What would happen — and why?
"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 a bigger hoop return from further away than a smaller hoop?
What happens to the return distance if you spin the hoop faster but throw it with the same force?
🧪 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 does the hoop come back?
When you add backspin to the hoop as you release it, two motions are fighting each other: the hoop is moving forward, and it is spinning backwards.
At the contact point with the floor, the forward slide creates friction acting backward against the hoop. That friction slows the forward motion and feeds energy into the spin.
Eventually the forward motion runs out. The spin is still there. The spin rolls the hoop back toward you.
• The backspin didn't disappear — friction converted the forward energy into rotational energy and stored it. Then friction cashed it in.
Why is friction the hero rather than the villain?
We usually think of friction as a force that slows things down. In this experiment, friction is the engine that reverses the hoop's direction.
• Without friction — on an ice rink, for example — a hoop with backspin would slide forward and stop. It couldn't return because there's nothing for the spin to grip.
• The hoop needs friction to reverse. The rougher the floor, the faster the friction acts, and the quicker and more dramatically the hoop returns.
Why does the slow throw fail, but the fast spin works?
A harder throw means more forward energy for friction to overcome before the spin can take over. Throw too hard, and the hoop stops at a wall or never fully reverses.
A stronger spin means more rotational energy stored for the return journey. Spin too weakly, and friction burns through it before the reversal is complete.
The balance between throw force and spin energy is the key variable. The hoop is a physical equation: the return distance tells you which side won.
Real-world connection
• A tennis player's topspin and backspin shots use this exact principle — spin stored in the ball interacts with the court surface on bounce, changing the ball's direction and speed.
Try next
• See another experiment where friction is the key to what happens — or doesn't → [The Ghost Glider]
• See Newton's First Law working on a spinning object in orbit → [The Runaway Planet]
Extension: G&T Years 5 & 6
Why does the hoop store energy in its spin?
When you throw the hoop with backspin, you’re giving it two kinds of energy at once:
forward motion (translation)
spin (rotation)
Friction at the floor doesn’t just slow the hoop — it moves energy from one form to the other. As the hoop slides, friction drains the forward motion but strengthens the spin. The return journey is simply the spin “paying back” the energy friction stored earlier.
Question: If you doubled the spin but kept the throw the same, how would the return distance change?
Why can friction reverse motion instead of stopping it?
Friction always acts at the contact point. With backspin, that contact point is trying to move backward relative to the floor. The floor pushes forward on that point — and that forward push is what eventually rolls the hoop back. Friction isn’t the villain here. It’s the steering wheel.
Vocabulary
Backspin: A type of spin where the bottom of the hoop moves backward relative to its direction of travel.
Friction: A force between surfaces that can slow motion — or transfer energy from sliding to spinning.
Energy transfer: When energy moves from one form to another. Friction transfers forward motion into spin in this experiment.
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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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