Whether you consider fidget spinners fun toys or incredibly annoying gadgets, there's actually a pretty significant amount of physics that goes into making them work. Fidget spinners are essentially little gyroscopes, bringing in these physical principles, but we can understand other concepts through playing with the spinning toys as well. By examining and studying fidget spinners, we can understand exponential decay, gyroscopic motion, friction, inertia, and much much more. Let's take a look at the physics behind fidget spinners.

[Image Source: *Pixabay*]

## Gyroscopic Motion

Fidget spinners are essentially pocket gyroscopes. Gyroscopes are spinning devices mounted on an axis used to provide stability to a body through the resistance of motion due to rotational momentum. You can understand this principle when spinning a fidget spinner. If you try to rotate the spinner in a way that is not parallel to it's rotational axis, you feel resistance from the spinner itself. Another crazy thing happens when you play with a fidget spinner, it doesn't always move in the way that you would expect.

Examining this in more detail, we are left with the principle of gyroscopic precession. You can see this at work if you take a fidget spinner and try to tilt it forward. Instead of the spinner tilting forward as you would like, it sort of tilts at a diagonal, relative to the direction the spinner is going. This diagonal rotation is a direct result of gyroscopic precession.

Gyroscopic precession is defined when a force is applied to a rotating body, a force appears 90 degrees after the point of impact in the direction of rotation. This is the exact principle at play when using a fidget spinner. So, now you can teach other people a little physics while you fidget away.

## Exponential Decay

Some people play with fidget spinners in order to improve their spin time. For many, spinning a fidget spinner is a lot less about fidgeting and a little more of a competition. If you have ever spent any time doing this, then you likely understand that it's really hard to drastically improve the spin time of your fidget spinner. It may make sense from a general perspective that spinning a spinner twice as hard or twice as fast would result in double the spin time, but that isn't even close to what actually happens. This is due to the principle of exponential decay.

The video above goes into great detail about how this principle works relative to fidget spinners, but we'll dive into it here as well. By observing how the frequency and thus the speed of a fidget spinner changes over time, we are left with a graph that demonstrates some near-perfect exponential behavior. Observing this, we see that as time goes on, the speed of a fidget spinner decreases exponentially over time. Taking this principle and applying the hypothesis that doubling the initial speed would double the time, we see that due to exponential decay, this only increases the time by something like a 1/5th. The actual time increase will vary dependent on the actual decay of your specific fidget spinner. A period of decay occurs every time the speed of the spinner halves and in the video above, it was 40 seconds.

Understanding exponential decay allows us to understand that there is a physical maximum amount of time that a fidget spinner can spin. We can try and try to increase the spinning of a spinner, but ultimately we are just fighting against the laws of physics themselves.

## Angular Velocity

Fidget spinners can be used as demonstration models for calculating angular velocity. By using a simple app on your smartphone that measures frequency, you can get your fidget spinner moving as fast as you can go and determine the highest frequency that it was spinning at. Now, depending on how many nodes your spinner has, typically 3 or 2, you have to divide that frequency by your respective amount. This is due to the fact that the sound measured frequency is how many times each node passes the microphone on your smartphone. Since you are trying to calculate the entire speed of the fidget spinner and there is more than one node, you have to divide by the respective number.

You should be left with a number of Hz that your fidget spinner was rotating. By measuring the radius of your fidget spinner and multiplying it by 2pi and the number of Hz you calculated you are left with a speed in the units you measured your radius in by seconds– probably inches/s or centimeters/s. By then converting these units into something like KPH or MPH, you can figure out the exact speed that your fidget spinner was spinning.

This is a great and fairly achievable way to teach your kids some physics and math all the while having fun with a new toy.