Love them or hate them, so-called fidget spinners are hitting a critical mass in pop culture — the millennial’s yo-yo. The fad’s meteoric rise is likely bolstered by social media, internet culture’s propensity towards distraction, and our love of niche gadgets, but once you get your hands on one, there’s something else. When you spin the toy, it feels like it comes alive, like it fights any motion to try to give it. The reason is physics.

Apply a force to any object with mass, and that object will gain some momentum. To change that object’s momentum again, like slowing down your car, you need to apply some force, as the friction between the brakes and the car’s wheels does. A fidget spinner isn’t moving like a car moves, but it does spin mass around an axis. That gives the toy angular momentum.

The angular momentum of a fidget spinner happens to point outwards from the spinner’s center. And so to change the direction of the momentum — rotating the spinner with your fingers — you must apply a force. You push on the spinner, and the spinner pushes back on you. That’s why a fidget spinner feels like it fights you, like it’s alive.

And how does a fidget spinner spin so satisfyingly long? The ball bearing at the center of the toy is a way to change the kind of friction it produces. By having small metal balls roll with the spinner as it moves, sliding friction is changed to rolling friction, which is necessarily much smaller in value. It’s like the difference in friction between your a car with skis and a car with wheels — the skis are going to bring the car to a stop much faster.

Even though there is no scientific evidence that fidget spinners are a true treatment for those with depression, ADHD, or on the autism spectrum (as many toys in a rudimentary search irresponsibly claim), they are certainly fun little distractions. Part of that has to be the physics.

—

Need more geeky science experiments? How about xenomorph blood!