How does spinning change the way something moves?
Fidget spinners are everywhere you look these days. They were popularised as something to do with your hands while you pay attention to important things, but have become popular as a toy for all ages and skill levels. While your teacher might not love when you have one in class, the physics behind the phenomenon are truly head-spinning!
Fidget spinners work due to their unique design: three weights spin in unison around a central bearing. The rapid movement of the weights combined with gravitational forces create the sensation of weight when manipulating the spinning toy. Today we are going to examine some of the fascinating science behind fidget spinners. Sure, they spin, but why do they spin so smoothly, and for so long? Why is it difficult to flip one over mid-spin? Let’s try to answer these questions with an experiment.
The pencil should stay balanced parallel to the ground and spin around in a circle. If that doesn’t happen, try spinning the fidget spinner the opposite direction and try again. This happens because of the way that a spinning object changes the way that forces act on it. This is called gyroscopic precession and happens when a spinning object is suspended on an axle. The torque or rotational force of the fidget spinner is pushing outward from the axle, in this case a pencil or chopstick, which allows it to stay suspended and turn slowly in a circle. Gyroscopic precession is what allows a bike to stay upright while it’s moving, and why you have to put your foot down to balance when you stop.
Be sure to clean up when you are all done. Throw the tape away and put the other materials back where you found them.
The way fidget spinners are built makes them great for this experiment, but that doesn't mean they are our only option. For example, bikes were mentioned, and if you have a bike wheel available, maybe you could find a way to set this up with a string or rope and a bike wheel in a garage or outside. What else can you find that you could easily spin on some kind of axle like a pencil, a chopstick, or a stick?
We suggested about 2.5cm between the fidget spinner and the string, but what happens if you use more or less distance? If you find some distances that don't work, can you figure out or research why they don't? If you're spinning other objects, what distances work for those specific objects, and why might they be different than, or the same as the distance for a fidget spinner?
Lastly, what happens if the string is moving? Does it change the behaviour of the spinning object? Does the way the string is moving make a difference? Remember to be aware of where you’re doing the experiment and what’s around you!
This experiment was selected for Science at Home because it teaches NGSS Disciplinary Core Ideas, which have broad importance within or across multiple science or engineering disciplines.
Learn more about how this experiment is based in NGSS Disciplinary Core Ideas.