## Intro

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I initially wanted to learn about how yo-yos work, but given that i do yo-yo in my free time, I was already familiar with the mechanics of a yo-yo (or at least the ones I own). So I then turned to finding the moment of inertia of one of my yo-yos. I realized that we had not gone over rotational motion in Physics B (and quite honestly, it was my worst unit in Physics C), but I hopped on this idea, and went with it.

How a Yo-yo works

I'm sure nearly everyone's thrown a yo-yo before, so the general shape of the yo-yo should be familiar to everyone, however, there are some aspects I'm sure most people have not seen before.

Yes, it is similar to traditional yo-yos in that it is similar in shape to a spool. It has string wrapped around the axle, and the yo-yo can go up and down. However, as opposed to a stationary axle, this yo-yo has a (10 or 8 ball) bearing inside that allows the yo-yo to spin for a much longer time and in doing so, makes the yo-yo less responsive. In previous yo-yos, when you want the yo-yo to come back up, a simple tug of the wrist would snap it back. Due to how yo-yos work, they require friction (between the string and the yo-yo) in order to fly back to your hand. However, due to the bearing inside, the yo-yo does not have enough friction to come up via tug, but instead relies on wrapping the string around an extra 1 or sometimes 2 times in order for there to be enough friction (this procedure is called a bind). I believe the bearing is probably the newest and most unfamiliar part to the yo-yo as the rest is pretty self explanatory.

How moment of inertia works

I find the best analogy for understanding what moment of inertia is, is inertial mass. Imagine that there is a giant block that is not under the force of gravity due to a celestial body, etc. Now, if one were to push the object, the block would still resist  the push depending on its mass. Similarly, moment of inertia is how much an object resists being rotated about a point. It's the mass equivalent of rotational bodies albeit much harder to calculate.

Also, below is a video of me spinning the bearing on a yo-yo.

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