How do yo-yos work?

220 views

[ad_1]

Never got to actually proper use one, saw one earlier and remembered that I don’t know how to use one.

So, how do they work? It just, makes zero sense to me

In: Physics
[ad_2]

You drop yo-yo. Yo-yo picks up speed as it falls. Strings unwinds, reachs the end and it’s moving so fast it just winds itself back up

The string the yo-yo is actually twice as long as it looks. It is folded in half and twisted back on itself. This forms a small loop at the end of the string.

When you throw the yo-yo, the unwinding of the string makes the yo-yo spin. The shaft that connects the two halves of the yo-yo together sits in the loop mentioned above. The spinning of the shaft and sitting in the end of the loop is what keeps it from coming back up right away.

Higher quality yo-yos actually have a small bearing around the central shaft. The bearing lets the shaft spin while the outside of the bearing either doesn’t spin or spins much more slowly.

The yo-yo comes back up when the string starts to wind back around the center shaft of the yo-yo.

From a physics standpoint, the yo-yo is a delicate balance between kinetic and static friction.

As stated, the yo-yo string is actually a doubled-over string where the midpoint loop has the yo-yo’s axle through it. Depending on how tight the string’s twist is will determine how much squeezing will be applied to the axle. As long as the yo-yo has enough rotational momentum to overcome the static friction limit to have the string “catch” the axle, it will continue to spin freely and slow down over time due to the kinetic friction of the axle and string rubbing together.

The technique of yo-yoing comes down to having control over when the string actually catches the axle. Ideally, you want to avoid anything that will cause a shock to the string — bouncing, snapback, etc. The reason for this is that any slack you give to the end of the string allows for the friction to take effect and catch back on the axle. Once enough of the string is wrapped around the axle, it will be enough to keep the string in place and start the yo-yo winding back up.

In order to get a good long spin going, a lot of technique is required to prevent the bounce once the string is unwound. Imagine that you’re in an elevator that’s crashing down to ground floor. It’s like trying to time a jump right before it hits the ground, so that you minimize the actual impact felt. That’s what’s happening to the string as the yo-yo unwinds — once it reaches the end of the winding, the yo-yo stops falling immediately, and will bounce back from hitting the end of the string’s slack.

 

At least, that’s how classic yo-yo’s work, with no extra mechanics involved. There are also mechanical-assist yo-yo’s which have a centrifugal clutch. These have weights that are held near the center with springs. Once the yo-yo is spinning fast enough, the weights will push against the springs and move outward, which releases the axle and allows it to spin freely on bearings. This means that even if you have a bounce or snap, as long as the axle is free, it’s not going to catch the string. This allows you to get *really* fast spins going, as well as have them last a *long* time since there’s a lot less friction involved.