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Author Topic: Rim weight vs Center weight?  (Read 2085 times)
Humphrey
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Re: Rim weight vs Center weight?
« Reply #20 on: October 25, 2011, 09:40:01 PM »

Weight distribution is about the distance from the center. The further the weight is, the more inertia it has in angular momentum. It's similar to why it's easier to unscrew a rusty bolt with a wrench than your fingers. The amount of work that can be done is greatly increased from the leverage you get.
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rizki_yoist
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-Rizki Hadiaturrasyid-


Re: Rim weight vs Center weight?
« Reply #21 on: October 26, 2011, 09:39:35 AM »

The Joshinator said everything I'm going to say, so I'll just add few things.
the analogy:
center weighted: Imagine using 1st gear in a car
rim weighted: Imagine using 2nd gear in a car

if you use exact same throwing power on both yoyos:
center weighted one accelerated better (feels light when thrown) but less rotating speed
center weighted one accelerated less (feels heavy when thrown) but more rotating speed

That's the simplest explanation I could think of.
« Last Edit: October 26, 2011, 09:40:35 AM by rizki_yoist » Logged

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Humphrey
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Re: Rim weight vs Center weight?
« Reply #22 on: October 26, 2011, 08:23:07 PM »

The Joshinator said everything I'm going to say, so I'll just add few things.
the analogy:
center weighted: Imagine using 1st gear in a car
rim weighted: Imagine using 2nd gear in a car

if you use exact same throwing power on both yoyos:
center weighted one accelerated better (feels light when thrown) but less rotating speed
center weighted one accelerated less (feels heavy when thrown) but more rotating speed

That's the simplest explanation I could think of.

This is false. Low numbered gears have larger diameters, allowing for more torque. A larger gear makes it easier to turn. So, a yoyo with a large percentage of rim weight would spin with more momentum, but slower in angular speed because of the increased distance. A center weighted yoyo will spin at higher rpms but will not spin for as long because there is less angular momentum.

Trucks have large gears so that they can tow large loads. They exert the force from the engine onto a larger gear, allowing for more torque to be exerted. Work = Force x Distance. If the same amount of force is applied at a distance, more work can be done.

Racecars may have large engines like trucks, but they have smaller transmissions. The engine must work harder to get the wheels to spin, but they will spin faster because one revolution of a small gear is less distance than a revolution of a large one.

/physics
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rizki_yoist
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-Rizki Hadiaturrasyid-


Re: Rim weight vs Center weight?
« Reply #23 on: October 27, 2011, 10:47:28 AM »

The Joshinator said everything I'm going to say, so I'll just add few things.
the analogy:
center weighted: Imagine using 1st gear in a car
rim weighted: Imagine using 2nd gear in a car

if you use exact same throwing power on both yoyos:
center weighted one accelerated better (feels light when thrown) but less rotating speed
center weighted one accelerated less (feels heavy when thrown) but more rotating speed

That's the simplest explanation I could think of.

This is false. Low numbered gears have larger diameters, allowing for more torque. A larger gear makes it easier to turn. So, a yoyo with a large percentage of rim weight would spin with more momentum, but slower in angular speed because of the increased distance. A center weighted yoyo will spin at higher rpms but will not spin for as long because there is less angular momentum.

Trucks have large gears so that they can tow large loads. They exert the force from the engine onto a larger gear, allowing for more torque to be exerted. Work = Force x Distance. If the same amount of force is applied at a distance, more work can be done.

Racecars may have large engines like trucks, but they have smaller transmissions. The engine must work harder to get the wheels to spin, but they will spin faster because one revolution of a small gear is less distance than a revolution of a large one.

/physics

You got me wrong, I'm not talking about the gear itself, just how you use engine rpm speed compared to car acceleration, sorry for unclear analogy here. Let me say, if there are two yoyos, one have bigger diameter while another have smaller diameter but they have same bearing size, that gear you're talking about is the bearing compared to the yoyo size/weight distribution. Small or less rim weighted yoyos is comparable to bigger gears in car, because the comparison between the bearing (gear) with the yoyo diameter (wheel) is less than bigger/more rim weighted yoyos.

So, what I wanna say is center weighted yoyos accelerated better but spin in less rpm compared to rim weighted one which accelerated slower (feels heavy) but spin in higher rpm, in case that you throw them in the same speed. (sorry I used to say strength instead of speed, it's my fault)

But if we're talking about the same strength then more rim weighted one should spin in less rpm but in more momentum, vice versa.

Sorry for my mistake here  Afro

edit: I think about that once again and I realized my stupidity...
If we throw two yoyos in the same speed (the amount of time from when it leaves your hand until it hits the string end) with the same bearing size, there will be no difference in rotating speed, because the bearing which are the same size, travels on the string in the same speed...
But if you throw them in the same strength then as Humprey said, rim weighted one will spin in less rpm but more momentum compared to the center weighted one.
ahh what happened with my brain!  tickedoff
« Last Edit: October 27, 2011, 11:06:53 AM by rizki_yoist » Logged
The Joshinator
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Re: Rim weight vs Center weight?
« Reply #24 on: October 27, 2011, 08:09:00 PM »

Totally different, but very interesting, thought here: technically, super-wide yoyos may actually be no more stable than narrower yoyos. I may be wrong, but I believe the resistance of a rotating object to change its axis depends not on how far it moves in 3 dimensions, but the angle through which you try to rotate it. With extra-wide yoyos, it's much easier to see a very small change of angle because the rims, which are far away from the center of tilting, move a lot more than a narrower yoyo for a given angle; the smaller of a tilt you can see, the sooner and easier you can correct for it and the more stable the yoyo is perceived to be.

In analogy, think of a bicycle wheel with a pole through the middle. When you tilt the bicycle wheel sideways, sections of the pole close to the wheel don't move very much, but the ends of the pole move a lot. Conversely, you can move the ends of the pole a noticeable amount, while the middle sections of the pole appear to not move at all. A narrow yoyo would be "toward the center" of the pole, where it can tilt a lot more before you notice it, whereas a super-wide yoyo would stretch all the way out to the "ends" of the pole, meaning any tilt at all is easily noticeable and correctable, thus contributing to the perception of stability.

(What made me think of this whole thing is an interactive exhibit a local science museum used to have. They had a large bike wheel with a short axle and a handle on each end, and a machine to spin it up. You'd hold the wheel vertically and sit in an office chair, and by trying to tilt the wheel sideways the gyroscopic torque on the wheel would cause the person and chair to turn around and around until the wheel ran out of energy. It was cool.)
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Humphrey
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Re: Rim weight vs Center weight?
« Reply #25 on: October 27, 2011, 09:03:43 PM »

Your reasoning seems sound, but I don't know those physics. It would make sense though; heavily rim weighted yoyos are more prone to wobble because they have more weight on the rims.

If the tolerances on those rims are off by a minute amount, it will have a greater effect on smoothness than if the error was closer to the center of the yoyo.
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i throw yoyos
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Re: Rim weight vs Center weight?
« Reply #26 on: November 24, 2011, 10:28:58 PM »

hmm i think if u have weight focused to the outtermost parts of the yoyo it will lower the center of gravity so the yoyo will tilt less thats the reason tight rop walkers carry poles so it just makes sense to me and ive heard center weight has an effect on smoothness maybe because it pulls mass towards the center increasing rotational speed and that somhow turns into smoothness just some thinking i did makes sense to me if im wrong about it correct me so i dont look dumb later on ^_^
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need-a-bow
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Re: Rim weight vs Center weight?
« Reply #27 on: November 24, 2011, 10:38:50 PM »

I thought that only applied when you have normal force and gravity applying on an object, not when you have tension acting on the object. But I'm almost failing physics so I could be wrong
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R-fly
The Chemist
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Re: Rim weight vs Center weight?
« Reply #28 on: November 25, 2011, 01:23:14 AM »

The Joshinator said everything I'm going to say, so I'll just add few things.
the analogy:
center weighted: Imagine using 1st gear in a car
rim weighted: Imagine using 2nd gear in a car

if you use exact same throwing power on both yoyos:
center weighted one accelerated better (feels light when thrown) but less rotating speed
center weighted one accelerated less (feels heavy when thrown) but more rotating speed

That's the simplest explanation I could think of.

This is false. Low numbered gears have larger diameters, allowing for more torque. A larger gear makes it easier to turn. So, a yoyo with a large percentage of rim weight would spin with more momentum, but slower in angular speed because of the increased distance. A center weighted yoyo will spin at higher rpms but will not spin for as long because there is less angular momentum.

Trucks have large gears so that they can tow large loads. They exert the force from the engine onto a larger gear, allowing for more torque to be exerted. Work = Force x Distance. If the same amount of force is applied at a distance, more work can be done.

Racecars may have large engines like trucks, but they have smaller transmissions. The engine must work harder to get the wheels to spin, but they will spin faster because one revolution of a small gear is less distance than a revolution of a large one.

/physics

Your physics here is breaking the first law of thermodynamics. to say a rim weighted yoyo would spin longer based on a higher moment of inertia (you said angular momentum but I don't think its what you meant since angular momentum here should be equal since L=Iw) isn't true. W= F x d for a linear system but W= t x theta or W= F x r x theta for a yoyo. Rim weighted has a higher torque yes but smaller theta.

As long as the yoyos are thrown with the same force work will be equal between the two. The only way one can lose to the other work wise is if we account for friction. Whichever loses more energy to heat will result in less work.
« Last Edit: November 25, 2011, 02:09:50 AM by R-fly » Logged
need-a-bow
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Re: Rim weight vs Center weight?
« Reply #29 on: November 25, 2011, 01:29:18 AM »

O.K. Let's not make this an episode of the big bang theory
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R-fly
The Chemist
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Re: Rim weight vs Center weight?
« Reply #30 on: November 25, 2011, 02:26:11 AM »

Your reasoning seems sound, but I don't know those physics. It would make sense though; heavily rim weighted yoyos are more prone to wobble because they have more weight on the rims.

If the tolerances on those rims are off by a minute amount, it will have a greater effect on smoothness than if the error was closer to the center of the yoyo.

Also not quite true. Rim weighted and center weighted would have different moment of inertias but different angular velocity so angular momentum is equal. This means they are equally resistant to wobble as long as external torque is equal. Joshinator was commenting on wide yoyos which are more prone to wobbe due to the larger external torque that would be applied assuming the angle of tilt when thrown is equal.
« Last Edit: November 25, 2011, 02:27:45 AM by R-fly » Logged
Humphrey
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Re: Rim weight vs Center weight?
« Reply #31 on: November 25, 2011, 07:25:05 PM »

The Joshinator said everything I'm going to say, so I'll just add few things.
the analogy:
center weighted: Imagine using 1st gear in a car
rim weighted: Imagine using 2nd gear in a car

if you use exact same throwing power on both yoyos:
center weighted one accelerated better (feels light when thrown) but less rotating speed
center weighted one accelerated less (feels heavy when thrown) but more rotating speed

That's the simplest explanation I could think of.

This is false. Low numbered gears have larger diameters, allowing for more torque. A larger gear makes it easier to turn. So, a yoyo with a large percentage of rim weight would spin with more momentum, but slower in angular speed because of the increased distance. A center weighted yoyo will spin at higher rpms but will not spin for as long because there is less angular momentum.

Trucks have large gears so that they can tow large loads. They exert the force from the engine onto a larger gear, allowing for more torque to be exerted. Work = Force x Distance. If the same amount of force is applied at a distance, more work can be done.

Racecars may have large engines like trucks, but they have smaller transmissions. The engine must work harder to get the wheels to spin, but they will spin faster because one revolution of a small gear is less distance than a revolution of a large one.

/physics

Your physics here is breaking the first law of thermodynamics. to say a rim weighted yoyo would spin longer based on a higher moment of inertia (you said angular momentum but I don't think its what you meant since angular momentum here should be equal since L=Iw) isn't true. W= F x d for a linear system but W= t x theta or W= F x r x theta for a yoyo. Rim weighted has a higher torque yes but smaller theta.

As long as the yoyos are thrown with the same force work will be equal between the two. The only way one can lose to the other work wise is if we account for friction. Whichever loses more energy to heat will result in less work.


Then why do rim weighted yoyos spin longer? Do they somehow have less friction? I don't think so.

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R-fly
The Chemist
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Re: Rim weight vs Center weight?
« Reply #32 on: November 25, 2011, 09:34:49 PM »

That's exactly why they spin longer. Energy of friction depends on distance as well as coefficient of friction much like work. The center weighted yoyo spins faster thus completes more revolutions which means it will lose more energy to friction. The two yoyos have the same angular momentum and total energy but rim weighted loses less to friction meaning more work and a longer spin time.
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Humphrey
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Re: Rim weight vs Center weight?
« Reply #33 on: November 25, 2011, 11:50:57 PM »

http://entertainment.howstuffworks.com/yo-yo2.htm

Changing the mass placement changes the moment of inertia. The moment of inertia would not be the same for a rim weighted and non rim weighted yoyo.
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The Joshinator
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Re: Rim weight vs Center weight?
« Reply #34 on: November 26, 2011, 12:40:57 AM »

Rim-weighted yoyos have the same amount of friction as center-weighted yoyos, but the weight at the rims has more "leverage", if you know what I mean, against the friction and the friction slows it down less. Just like if you have a ball of Styrofoam rolling on the carpet and an identically-sized steel ball bearing rolling on the same carpet, the steel one will go farther and get slowed down less by friction because it has more inertia. In a yoyo, however (or in any rotational system), it's not the actual quantity of mass that determines its rotational inertia but where the mass is placed relative to the axis of rotation, so you can have two yoyos with the same weight but different weight placements that will be affected differently by friction near the center.
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R-fly
The Chemist
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Re: Rim weight vs Center weight?
« Reply #35 on: November 26, 2011, 03:27:24 AM »

http://entertainment.howstuffworks.com/yo-yo2.htm

Changing the mass placement changes the moment of inertia. The moment of inertia would not be the same for a rim weighted and non rim weighted yoyo.

I am not disputing that a rim weight has a higher moment of inertia but what matters here is angular momentum and that includes angular velocity as well as moment of inertia. Rim weight has higher moment but lower angular velocity.
« Last Edit: November 26, 2011, 03:58:43 AM by R-fly » Logged
R-fly
The Chemist
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Re: Rim weight vs Center weight?
« Reply #36 on: November 26, 2011, 03:57:17 AM »

Rim-weighted yoyos have the same amount of friction as center-weighted yoyos, but the weight at the rims has more "leverage", if you know what I mean, against the friction and the friction slows it down less. Just like if you have a ball of Styrofoam rolling on the carpet and an identically-sized steel ball bearing rolling on the same carpet, the steel one will go farther and get slowed down less by friction because it has more inertia. In a yoyo, however (or in any rotational system), it's not the actual quantity of mass that determines its rotational inertia but where the mass is placed relative to the axis of rotation, so you can have two yoyos with the same weight but different weight placements that will be affected differently by friction near the center.

Again I think moment of inertia and angular momentum are being confused. In your analogy the ball bearing would go further because it has a higher moment and angular momentum. The two cases are not analogous because our two yoyos would have the same angular momentum. The reason the center weight spins less is because more rotations equals more energy lost to friction. Rim weight and center weight have the same friction per rotation but not same total energy lost to friction because a center weight will go through more rotations. Also mass absolutely matters in rotational inertia I=m x r^2.

Rim weight does have a higher resistance to change in its rotation rate but since its rotating slower from the start you don't have to change its rate as much to stop it. Angular momentum is the difficulty in bringing an object to rest and that is the issue here.
« Last Edit: November 26, 2011, 04:18:24 AM by R-fly » Logged
Humphrey
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Re: Rim weight vs Center weight?
« Reply #37 on: November 26, 2011, 02:05:24 PM »

Rim weight has more angular momentum. It is harder to stop. By your formula, rotation inertia is mass times radius squared. The radius will have more effect on the inertia than mass because it is squared. If r is larger the momentum would be greatly increased. Rim weighted yoyos have more momentum.
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Kyle Derry
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immortal


Re: Rim weight vs Center weight?
« Reply #38 on: November 27, 2011, 02:34:08 PM »

Very interesting read guys.
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888alltheway
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Herp the Derp


Re: Rim weight vs Center weight?
« Reply #39 on: November 27, 2011, 09:41:19 PM »

We should post this question on /r/askscience. Everyone on /r/askscience is a genius.

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