yoyo physics question

Not necesarily. The force you’re applying via string tension (to do an around the world) acts on the whole mass of the yoyo uniformly. This is equivilent to saying that, neglecting spin, every point of mass in the yoyo moves togeather (i.e. the yoyo doesn’t start to spin or fly apart as a result of the force).

The reason we can neglect spin is that, if it took more energy to move a spinning yoyo, that energy would have to go somewhere that it couldn’t in a dead yoyo. Kinetic energy is equal to .5mv^2 + .5Iw^2 where m is mass v is velocity, I is moment of inertia (a function of mass distribution) and w is angular velocity. Since pulling on a yoyo doesn’t make is spin faster or slower (i.e. doesn’t change the angular velocity), all the energy you put into the system via pulling the string must go into increasing the regular velocity.

If the force you’re applying acts on every particle in the yoyo with the same strength, so they react by moving in the same direction with the same increase in velocity. Therefor, the reaction of all those paricles togeather is equal to the reaction of one of those particles times the amount of particles in there (since they’re all the same). Therefor, the way a yoyo reacts to a centripital force that makes it do an around the world only depends on the number of particles in it, or in other words, it’s mass.

Ok, you’re completely losing me here…

Centripetal force is kinematic not kinetic. That equation for KE is just… I don’t know… What are you actually trying to say with it?

That last paragraph is decidedly unclear. Your explanation of Newtonian(?) physics is throwing the Standard Model right out the window. What particles are you referring to in particular?


i think he means the atoms of matter in the yoyo

Yeah, that’s what I was figuring. For the purposes of this discussion, however, most of the physics we’re trying to get to the bottom of are happening on the subatomic level. Should we need to delve into detail, this should probably be the way to go with it.

Doc, you’re right to be confused.

My explanation sucked. I didn’t really understand what was going on with forces, so I switched to an energy based explanation half way through. The particle stuff was totally unnecessary, too. I thought about it some more, and I think I can do a much better job explaining what I think is going on, but it’ll take me a while and I have to write an essay (laaaaame). Anyway, I’ll probably get to chance to do all that later on tonight, but for now I just wanted to apologize for that.

Don’t apologize, I’ve thoroughly enjoyed reading through your thought process.

This is an interesting question, because although it seems obvious that the feel is different via trial, the proof for it is not as simple or concise as I’d expect.

Don’t worry about it!

The particle stuff is quite necessary, don’t shy away from it. Unless someone has a more simplified explanation, might as well start at the bottom and work our way up.

Because a rim weighted is more stable and harder to move? (ex. The Bhudda yoyo. The one that made the world records.) So it feels less floaty when center weighted are less stable and easier to flip.(ex. As in looping.) So it takes more effort to flip a yoyo with more rim weight, which accounts for sluggishness or not floaty. And those with weight in the center is more floaty, because it’s easier to be moved/flipped/looped.

that’s as good of a theory we have so far

Really? I was just thinking of looping and all that. It’s not that Physicy, but I guess it’s more of using examples to prove it.

when i think of it in 1a terms, it makes perfect sence and it probubly has a good deal to do with what is going on

Find the Langrangian. Then you can solve anything ;D

Can you even begin to imagine what that formula would look like on paper? Why on earth would any rational human being subject themselves to a torture so insidious as the one you’ve suggested?

I would rather scoot down a Slip-n-Slide of razorblades and kosher salt, to eventually reach the little “pool” at the end filled with lemon juice, than attempt what you’ve suggested.

I’m not even going to mention the breakdown of conservation laws this would necessitate…

Edit: You’re a sick monster.

Edit 2: P.S. What’s wrong wit’chu?

Why is it that complicated? I may be missing something but, assuming that we’re talking about a yoyo here we can express its potential energy as V=mgh if we define h=0 to be where the yoyo is hanging at rest from the the fully extended string and the Kinetic energy can be expressed as T=Tlinear+Trotational=.5(mv^2+Iw^2) So the Lagrangian for this particular case would be L= T-V = .5(mv^2+Iw^2)-mgh and then we express v and w in terms of time derivatives of position h and then we apply the Euler-Lagrange relationship d/dt(dpartial(L)/dpartial(q’))=dpartial(L)/dpartial(q)) where q and q’ are arbitrary coordinates. Unless i’m missing something this isn’t overly complicated (providing one has had the necessary math to facilitate the computation).

One of the reasons that this particular problem (the physics of yo-yos) is some complicated is because there are so many variables that change with EVERY throw. How clean is the bearing? Where is the string positioned in relation the center of the yo-yo? What’s the amount of friction between that particular string, and that particular response? How is the breeze blowing? I’m not even scratching the surface here either.

How would your equation take into account the changing coordinates based on the tension of the string?

I wouldn’t want to see what an ‘end-all’ equation for the dynamics of yo-yos would even look like.

You are over complicating, the idea is to break yo-yos down into comparable format… this isn’t that hard, you just have to assign some reasonable constants to certain areas, and ignore things that don’t have any large significance (most of the things you listed)

I expected this thread to be filled with a bunch of bs… it’s not that bad really. Batryn is probably the closest to the actual answer here…

For those who don’t know who I am… I’ve spent the last 10 years on this subject… I’ve built real ‘programs’ to analyze 3d models, I’ve broken down the idea of ‘feel’ into its basic elements mathematically. (No, I’m not sharing all that, as I still use it to design stuff (many things outside of yoyos as well), sorry)

You should all buy Don Watson’s Yo-Yo Physics books (there are 5 of them)… he covers all sorts of stuff that may help you understand what’s going on. It’s not subatomic, yo-yos just aren’t -that- complicated… it’s simply applying all the physics involved.

RPM actually has a great deal to do with how a yo-yo ‘feels’ as well… guess what determines the RPM of your yo-yo? Weight distribution.

High Rim Weight = Low RPM
Low Rim Weight = High RPM

Those aren’t the only factors by a long shot… where the weight is placed in relation to the center of your mass (not just diameter, but actual distance across the x and y axis and the angle), the moment of inertia of the yo-yo, the list goes on. These will all ultimately change the effort required to change the direction of the yo-yo… that’s the ‘floaty’ feel you’re referring to.

Each yo-yo is a combination of all these things which give it a particular feel… that feel will (generally) be the same across all rpm ranges, so just changing the strength of your throw won’t truly demonstrate the point… however strength of -your- average throw does often influence why one person prefers a particular setup over another.

That’s all for now…


I agree.

I over complicated it for a specific reason, and that was to show that an all encompassing formula just isn’t the answer to the question.

I don’t know anything about engineering yo-yos, the only thing I know anything about hands on engineering wise is super-chargers. All I can say is that you don’t waste your time with the superficial stuff. Mathematicians and engineers are lazy. If the work doesn’t need to be done, their not going to waste their precious time crunching the numbers.

This thread is starting to get “thick” now…

I’m the one who mentioned the physics took place on a subatomic level. I wasn’t off-base with that. ALL physics occur on a subatomic level. For a yo-yo, yeah, it’s probably over-complicating things quite a bit, but I suggested it believing it would be a neat thought exercise if anyone was capable of putting that much thought into it. That’s all.

But, this thread is still interesting, so I’m curious to see where it goes from here.

‘neat’ is often simply a typo for ‘useless’ :slight_smile:

I’m quite capable of ‘putting that much thought into it’ but there is absolutely no reason to.


I find it interesting that you might take my words as an insult to your intelligence or ability. This wasn’t meant to be the case, to be clear. So, with that, I apologize to you if there was some misunderstanding. I was simply agreeing with you that high energy physics might be a touch complex to describe a yo-yo. Sure, it’s a arguably useless exercise. Doesn’t make it not fun!

But enough of that. I’m fairly sure I know what’s going on here, so let’s just get this out of the way so we can move past it quickly…

Your credentials aren’t in question here, at least not by myself. Perhaps you could further enlighten us on the matter at hand? You’ve apparently done over a decade of independent research on the matter, so further input would be greatly appreciated.