Held Up Without Glue! The Magic of Friction from Just Two Toothbrushes
I’m Ken Kuwako, a Science Trainer. Every day is an experiment!
Can you imagine a toothbrush suddenly transforming into a heavy-lifting powerhouse? We’re going to show you an experiment where a simple tool, usually just for cleaning teeth, unleashes astonishing power through the magic of science. It’s a perfect, everyday trick to experience the fun of physics!
The Experiment: Toothbrush vs. Banana! Which Wins?
All you need are two toothbrushes with firm bristles. The procedure is incredibly simple, but the result is shocking.
First, hang one toothbrush from a high spot using an S-hook or similar item.
Next, take the second toothbrush and mesh its bristles tightly with the hanging brush’s bristles, gripping them firmly together.
While lightly pressing the meshed section with your fingers, attach a weight to the bottom brush.
We decided to hang an entire bunch of bananas! That’s quite a load, isn’t it? You’d assume it must fall, but when you release your fingers…
The Amazing Result: It Holds!
Incredibly, the bottom toothbrush doesn’t slip! It firmly supports the bunch of bananas! We didn’t use any glue or tape—just the interlocking action of the bristles.
Science Explained: The Tiny Forces that Add Up to “Friction”
How is this possible? The secret lies in friction.
Each individual bristle on a toothbrush is weak and only exerts a tiny amount of force. However, a toothbrush is packed with hundreds, even thousands, of bristles. When you mesh the two brushes together, each bristle rubs against the others and slightly bends. The attempt of the bristles to straighten back out creates a strong squeezing force between the brushes, which in turn generates friction.
“Tiny Frictional Force per Bristle × Hundreds of Bristles”
This simple addition of forces creates an enormous cumulative frictional force—enough to support a whole bunch of bananas!
The Same Principle as the Famous Phone Book Trick
If this phenomenon sounds familiar, you might be remembering a famous experiment seen on TV or at science shows.
That’s right—the experiment where two interleaved phone books cannot be pulled apart, even by strong adults! In that case, the frictional force from each individual sheet of paper is small, but when hundreds of pages overlap, the combined force becomes powerful enough to tow a car.
This toothbrush experiment is essentially a “miniature version” of the phone book challenge! It’s exciting because you can experience this amazing law of physics using simple, affordable items you might even find at a dollar store.
Conclusion: The Hidden Power in the Mundane
We rarely think about the benefits of friction, but it’s why your sneakers don’t slip, and why Velcro (hook-and-loop fasteners) sticks. Velcro, in fact, was invented by observing how plant burrs cling to animal fur—a principle very similar to the “structural friction” we see in this toothbrush experiment.
I was genuinely surprised to learn a toothbrush could be used for such a demonstration. Please try this at home or in the classroom. You’ll find discoveries far more exciting than anything in a science textbook!
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We aim to make the wonders and fun of science more accessible! We compile easy-to-understand information on fun science experiments you can do at home and the tips behind them. Feel free to browse around! ・The content of our Science Idea Notebook has been published as a book. Details here. ・Find out more about the administrator, Ken Kuwako, here. ・For various requests (writing, lectures, workshops, TV supervision, appearances, etc.), click here. ・Article updates are delivered on X!
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