The Ghost Glider
A disc with a balloon on top slides across the table like it has forgotten how friction works. One push and it just keeps going — gliding almost silently, with almost nothing to slow it down.
7-12 yrs
Medium
20
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 Ghost Glider
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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 old CD or DVD
1 pop-top sports drink bottle lid
Hot glue gun + glue sticks — adult/teacher use only, done before class
1 round balloon — standard size, 25–30 cm when inflated
A smooth, flat surface: desk, table, or smooth floor — NOT carpet
Optional: tape measure to record glide distance
Coins, blue tack, etc. for added mass.
Let’s Investigate
1
Build Base
Using the hot glue gun, attach the pop-top bottle lid to the centre of the CD — centred as precisely as possible over the central hole.
Apply glue generously around the base of the cap and press it firmly.
3
The Control
With the valve pushed closed, give the Ghost Glider a consistent, gentle push across the smooth surface.
Measure or estimate how far it travels before stopping. Repeat twice and record both distances.
This is your control — the disc with normal friction, no air cushion.
5
Change a vairable
Now add mass to the disc and see if that changes how far ot travels.
2
The prediction
Before the balloon is attached, place the Ghost Glider base (CD + cap) on the smooth surface with the valve closed.
if you give this disc a gentle push — exactly the same push you would give a regular book across a desk — how far will it slide?
4
Now with air cushion
Release the air and push again with the same force.
Does the distance travel change? How?
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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.
Friction is always there. The only way to reduce it is to change what's actually in contact.
But what if you could make a disc float just above the surface — not quite touching — without using ice, oil, or any special material?
One household item can do it. Predict: what is it — and how would it work?
Write it down before you see the answer.
You just watched a disc glide across the table with almost nothing slowing it down.
Think back to the exact moment you opened the valve. Describe what changed in the disc's movement.
Compare the valve-closed glide and the valve-open glide. Describe the difference as precisely as you can — distance, speed, sound.
When the balloon ran out of air, the disc stopped almost immediately. What changed at that moment — and what does that tell you about what was doing the work?
You could barely hear the Ghost Glider moving. Friction usually makes a sound. What does the near-silence tell you about what was happening between the disc and the table?
Friction needs two surfaces in contact. Remove the contact — and friction almost disappears.
The air cushion lifted the CD just enough. Not floating — hovering. Riding on a thin layer of escaping air.
Real hovercrafts use industrial fans to maintain the air cushion continuously — your balloon runs out. What would you need to build a Ghost Glider that kept going indefinitely?
"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 air in the balloon change how far the Ghost Glider travels?
What happens to the glide distance if you add extra weight on top of the disc?
🧪 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 disc glide so far?
When the valve opens, air from the balloon rushes through the bottle cap and out the hole in the centre of the CD. This creates a thin cushion of pressurised air between the disc and the surface.
That cushion lifts the CD a fraction of a millimetre off the table. The disc is no longer touching the surface directly.
Friction needs two surfaces in contact to exist.
Remove the contact, and friction almost disappears. One gentle push sends the disc gliding with almost nothing to slow it down.
Why does the air cushion work when a regular push doesn't?
A book pushed across a desk stays in contact with the surface the whole time. Every millimetre of travel involves friction between book and desk.
The Ghost Glider's disc is riding on air — the actual surfaces never touch. The friction that would have acted simply has no surfaces to act between.
This is why hovercrafts can travel across water, ice, mud, and land equally well: none of those surfaces matters if you never touch them.
Why does it stops instantly when the balloon empties?
As the balloon empties, air pressure through the hole drops. The cushion thins. Eventually, the disc settles back onto the surface.
The moment contact is restored, friction returns — and the disc stops quickly.
Real-world connection
Real hovercrafts use exactly this principle at a larger scale — a flexible skirt traps a cushion of high-pressure air beneath the hull, lifting the craft above whatever surface it's crossing.
Maglev trains use magnetic levitation to remove contact with the track entirely, eliminating friction and allowing speeds above 600 km/h.
Try next
For a completely different role for friction — where it actively reverses a direction of travel — see [The Disobedient Hoop]. And in [Newton's Question: Who Moves?], friction against the floor is the only force that can prevent motion on rolling surfaces — which is why a smooth floor is essential for that experiment to work.
Extension: G&T Years 5 & 6
Why does friction disappear on an air cushion?
Friction only exists when two surfaces are touching. (as it is a contact force)
When the balloon pushes air through the bottle cap, that air spreads out under the CD and forms a thin, pressurised layer.
The disc lifts a tiny fraction of a millimetre — just enough that the plastic never actually touches the table. No contact → almost no friction → almost no slowing down.
Question: If the air cushion were twice as thick, would the disc glide farther, shorter, or the same? Explain your reasoning.
Why does the disc glide so smoothly?
On a normal surface, friction is messy: tiny bumps, scratches, and dust particles all grab at the object.
But an air cushion is perfectly smooth. Every point under the disc is supported equally.
This is why the glider feels “slippery” — the air removes the roughness of the surface.
Question: Why do ice skaters glide farther on smooth ice than on rough ice? What does that tell you about friction?
Vocabulary
Friction: A force that resists motion when two surfaces touch. The air cushion removes this contact, so friction almost disappears.
Air cushion: A thin layer of pressurised air that lifts an object slightly off a surface, reducing friction.
Pressure: How strongly air pushes on a surface. The balloon creates high pressure under the disc, lifting it.
Hovercraft: A vehicle that rides on a cushion of air instead of touching the ground, reducing friction and allowing smooth travel.
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READY TO TEACH THIS
TOMORROW?
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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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