Whether you played with one once or owned several, fidget spinners where the must have item of 2017. The fad’s upward thrust is in part thanks to social media, our culture’s love for distraction, and the fascination for niche items, but once you get your hands on one, there is something else. When the toy is spun it feels alive and fights any motion given to it. The reason is physics.
Each time force is applied to an object it gains momentum. In order to change that object’s momentum, like slowing down a car, more force needs to be applied. In a car this additional force is the friction between the brakes and wheels of the car. Fidget spinners don’t move like a car, but it does spin around an axis. This gives it angular momentum.
In a fidget spinner the angular momentum points outwards from the center of the spinner. To change the direction of the momentum force needs to be applied. With a fidget spinner this is done by pushing on the spinner and the spinner pushed back. Doing this feels like the fidget spinner is fighting you, like it’s alive.
What makes the fidget spinner spin for a satisfyingly long time? Ball bearings found at the center of the toy change the type of friction being produced. Small metal balls roll as the spinner spins. This changes sliding friction to rolling friction which is a smaller value. This is similar to a car stopping on wheels or on skis. The skis will stop the car much faster.
There isn’t any scientific evidence fidget spinners are a treatment for ADHD or depression as some toys in this area claim. They are a fun distraction thanks to physics.