-
NESA Accredited Teacher
-
High school chemistry & physics specialist 30+ years
-
The Crazy Scientist in primary schools — 15 years
-
International conference presenter on science education
-
Creator of the LAB™ Learning System
-
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
One metal coat hanger
Two pieces of string — approximately 30–40 cm each
A hard surface to knock the hanger against
How to do it
1
Tie the stringds
Cut or measure two pieces of string approximately 30–40 cm each.
Tie one end of each string to the two lower corners of the metal coat hanger — one string per corner.
3
Prediction
Now you are going to press the string ends against your ears before knocking it again.
Before you do: predict — will the sound be louder, softer, or something else entirely?
5
Knock Again
With your fingertips in your ears and the hanger hanging freely, have a partner gently knock the coat hanger against a hard surface — or swing it yourself so it taps against a desk edge.
2
Hold in Air
Before touching the string to your ears at all: hold the coat hanger up by the hook with one hand and knock it firmly against the edge of a desk or a doorframe.
Listen carefully. Then describe what you heard — in as much detail as possible.
4
Fingers in Ears
Wrap the free end of each string once or twice around your index finger — one string per hand.
Hold your hands apart so the coat hanger hangs freely between them. Now gently but firmly press both index fingertips into your ear canals.
Teacher Tip: Technique matters here. Students who loosely hold the string near their ears will get a weaker effect — the string needs to be in contact with the ear canal itself, not just near it.
Did it work? Share the science! Tag @the_crazy_scientist on Instagram — we love seeing your experiments!
Singing Coat Hanger
Designed by Darin Carr (BSc, DipEd)
NESA Accredited Teacher Chemistry & Physics Specialist
Creator of the LAB™ Learning System
A metal coat hanger doesn't look much like a musical instrument. Knock it against the edge of a desk and you'll get a dull, forgettable clunk. But connect it to your ears with two pieces of string — and it sings.
5-12 yrs
Easy
10
min
>
Singing Coat Hanger
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
-
LINK to what they already know,
-
ACTIVATE curiosity through hands-on discovery
-
BUILD understanding that actually sticks.
Think about every sound you've heard today. Your teacher's voice. A door closing. Music. We hear almost everything through air. It's so constant we never question whether it's the best option.
Here's your challenge before you touch anything: pick up the coat hanger and knock it against the edge of your desk. Listen carefully.
Describe what you hear — how loud, how long, how clear. Write it down in as much detail as you can.
Write your prediction: if you connected the string directly to your ears before knocking, do you think the sound would be louder, softer, or something else?
Now compare it to what you heard through the string. Go beyond "louder" — what else changed? What, if anything, stayed exactly the same?
Did the pitch change? The length of the sound? The quality? What does the string version remind you of — what real-world object or place does that sound belong to?
What was the only thing that changed between the two knocks — and what do you think was travelling through the string that wasn't reaching your ears through the air?
You just heard what happens when a vibration travels through a solid directly to your ear instead of spreading through a room of air. That difference — solid path vs air path — is doing something important in tools and technologies all around you.
A doctor's stethoscope doesn't broadcast a patient's heartbeat into the room — it carries the sound through rubber tubing directly to the doctor's ears.
Based on what you just experienced, why would a tube produce a clearer heartbeat than just pressing your ear against someone's chest and listening through the air?
"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 surface you knock the hanger against change the sound — does a wooden desk, a metal pole, a glass surface, or a carpeted floor produce a different resonance?
Does the type of string change the sound — does wool, cotton, fishing line, or twine carry the vibration differently?
🧪 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
The coat hanger didn't change. The knock didn't change. What changed was the path.
Sound is a wave (a vibration of energy) that needs a medium to travel through (these types of waves are called mechanical waves
When the hanger strikes a surface and vibrates, it creates sound waves that radiate outward in all directions through the air.
Air molecules are relatively far apart and loosely connected. As the sound wave spreads, the energy is distributed across an ever-larger sphere of air, losing intensity rapidly. By the time those waves reach your ears across a room, most of the energy is gone. What you hear is a soft, brief clunk.
When you press the string ends against your ear canals, you create a completely different pathway.
The vibration travels: metal hanger → string fibres → finger bones → ear canal.
Every link in that chain is a solid. In a solid, molecules are packed tightly together.
When one molecule vibrates, it immediately and efficiently passes that vibration to its neighbour, which passes it to the next — with very little energy lost between them. The vibration travels the full length of the string and arrives at your ear with most of its energy still intact.
The result is the full resonance of the coat hanger — rich, sustained, surprisingly loud — because you've bypassed the air entirely and delivered the vibration directly.
Curiosity spark: The coat hanger is metal. What do you think would happen if you used a plastic coat hanger instead — would it produce the same rich tone, or something different? What is it about metal specifically that makes it sing?
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
-
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.
