Wheel weight- 3x more?

Discussion in 'Observed Trials Discussion' started by stocktrials, Jul 21, 2004.

  1. stocktrials

    stocktrials Mitch.

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    OK I was listening to triple J today and someone rang up saying his bike mechanic told him that a bike wheel weighed 3 times more when it was rolling.

    When he asked him to explain the science behind it, the mechanic said that he didn't know but "it works".

    Dr Karl (resident radio scientist) couldn't explain it either and i was just curious if anyone knew the science or physics or whatever behind this??


    Not sure if it has something to do with rotational mass, air volume or whether he meant that it "weighs" 3x more because you are moving it with your feet as opposed to carrying it with your hands, so it "feels" heavier??

    Hope someone has an answer
     
  2. WhiteRavenKS

    WhiteRavenKS Well-Known Member

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    when something goes faster, it has more apparent mass. this doesnt really matter though since you have to be hauling tons of ass. like if you go close to the speed of light you "gain weight" faster than you can propel what you had forward (which is a really crappy explanation as to why we cant exceed the speed of light in a conventional sense). so anyways, when your wheels are wizzin along they do have more apparent weight but in reality it's not all that different. in the scales involved in biking i would think you should need some pretty sensitive crap to even measure the changes. i could be wrong though. i probably am.
     

  3. DanBowhers

    DanBowhers I farted.

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    I dunno if I have an answer but when my wheel (hookworm on a rhyno lite is spinning fast it is super hard to turn. I think its the gyroscopic affect that the weight of the wheel has. If you spin the wheel there is a force being applied to keep the wheel moving straight down around it's axis (the hub) turning that wheel becomes more difficult That force is energy that you have to fight to displace when you attempt to turn the wheel. For the most part its not terribly difficult. Think about how easy it is to turn your static wheel. I think it would only become an issue for super heavy wheels (like mine) with little resistance (ie in the air) and a big turn (ie x up)

    wow, did that make sense?
     
  4. xxxfr

    xxxfr RCP FABRICATION

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    just ride ur damn bike......the wheel my feel heavier due to the spinning.....but does your bike weigh more when your rolling....hell fuck no
     
  5. WhiteRavenKS

    WhiteRavenKS Well-Known Member

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    actually it does... he's asking a simple question becuase he's curious about what science (if any) went behind something he heard today... its not like he asked if it would affect him in his trials riding in any way. but thanks for that awesomely insightful post.

    dan- what you said does make sense. but a light weight wheel can be hard to turn also, just has to be spinning faster to get the same outcome as your heavier wheel.
     
  6. Elan

    Elan steve french

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    one time i went like 20mph on my koxx. it was crazy
     
  7. xxxfr

    xxxfr RCP FABRICATION

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    if it physically weighs more, then y doesnt the stand w/ the scale i work on go up when i pedal the bikes? i think its going to take more than pedaling speed to have a noticable difference if it really does change it
     
  8. RomanC

    RomanC Well-Known Member

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    This has to do with angular momentum and the gyroscopic effect because of it. As far as the wheel weighing 3 times as much. I think they just mean that the wheel experiences up to 3g when its spinning. (kinda like you get more Gs in a centrifuge when you spin really fast)

    As far as the speed of light goes. Basically you end up needing infinite energy to go that fast if you have any mass.



    Edit: http://hyperphysics.phy-astr.gsu.edu/hbase/amom.html this hase a nice illustration about angular momentum
     
    Last edited: Jul 22, 2004
  9. Elan

    Elan steve french

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    like traveling through a balck hole...but if they had infitine energy, wouldnt we ( EARF) already be inside of one's vagina?
     
  10. tomacropod

    tomacropod Rum Pig

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    perhaps he was referring to the old idiom that a given mass at the hub of a wheel is worth 3x that at the outside of the wheel? Not sure if this is quantitatively correct, especially given that wheels come in all different diameters and therefore have very different external speeds (from which stems the inertia of the wheel, as Arthur C Clarke noted in Rendezvous with Rama, there is no mysterious rotational force, only garden variety inertia) but the science behind the gyroscopic effect eluded me for many years. Anyway...I forgot what I was really going to say.

    - Joel
     
  11. hydroboy

    hydroboy "Jak se mas"

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    " To accelerate a wheel or pedal and shoe system, kinetic energy of rotation must be supplied, in addition to the kinetic energy of linear motion. For example, with a wheel, if the weight is mostly concentrated in the rim and tire it would take nearly double the energy needed to accelerate it than an equal non-rotating weight. In other words, one pound added to a wheel or shoe/pedal system is equivalent to nearly two pounds on the bicycle frame."
     
  12. hydroboy

    hydroboy "Jak se mas"

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    wait i just read the question again and it says "when it is rolling", i, well whatever page i quoted that from, was talking about accelerating the wheel. I dont think it will weigh anymore if its spinning or not.
     
  13. tomacropod

    tomacropod Rum Pig

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    I don't see how it would weigh any more when spinning, all the extra inertia from the rotating wheel would cancel itself out, being equal in all directions (unless you want to get nitpicking about unevenly weighted wheels, I don't). Wheels with less weight on the outside are easier to accelerate and decelerate, and easier to change direction, but other than that I don't know if there are any other hidden physics quirks. If there were any weight increases, I'm sure the large area (and industry) of flywheel physics would have picked it up. Look at websites devoted to flywheels, which run on the same principle of inertia, but use it as an advantage, rather than a hindrance.

    - Joel
     
  14. hydroboy

    hydroboy "Jak se mas"

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    i have noticed one thing, my bike feels much heavier when i pedal uphill, especially when i drag my brakes slightly.
     
  15. stocktrials

    stocktrials Mitch.

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    haha thanks for speaking on my behalf kevin.. :p
    And thanks Joel, Alex and everyone else who contributed.. although I will have to read and synthesise it a few more times before I fully understand it all!


    xxxfr- I am going to ride my bike.. just for you
     
  16. EchoPure89

    EchoPure89 Guest

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    when i swited rear tires, the new tire was ~300gs lighter and i felt a very noticible difference, my entire bike felt about 3lbs lighter and much more manuaverable. throwing the bike to rear wheel was a lot easier, i got about 3-5inchs farther than expected. to bad that tire was a peice of shit, ill stay with heavy ol' michy.
     
  17. Cryo-Cube

    Cryo-Cube -----------

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    yes, the mass increases with speed, but thats not important on human scales because "you have to reach 14% of the speed of light, or about 42 million m/s before you change the mass by 1%."

    So basically, superman riding a bike at 4000 miles/s would change the bikes mass by1%, a normal guy would change the mass by like 0,000000001%
     
  18. pav

    pav New Member

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    Firstly this may not be 100% accurate but is true from what i have learnt.

    I dont think that a wheel has more 'weight' when it is spining, just more force.
    It does feel heavier though. If you have ever held a wheel that is spinning at high speed by the axle it feels heavier and is very hard to move around. This would most likely be because of the fact that the wheel would have torque, which is given by the equation (i think):
    Torque = Radius x Force
    But yeh sparing all the crap if you sit on a spinny chair and hold a spinnign wheel by the axle horizontally it will make you spin around in the chair depending on which way the wheel is spinning changes the direction that you spin.
    So, it does not carry more wieght necessarily it just has more force making it feel heavier but you could use this to your advantage if you knew enough about the physics behind it.
    A spinning wheel will give you momentum as it does in the spinny chair experiment and also a high speed spinnnig wheel will be harder to move laterally so there fore also helping to balance you out.

    The lesson

    Don't use your brakes! Let your wheels spin. It does more than just look cool!

    pav

    ...yeh i know im a nerd...
     
    Last edited: Jul 22, 2004
  19. Gurra

    Gurra Porna Veselo Zadorno

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    It weights more because a person sits on it? :D
     
  20. Coramoor

    Coramoor New Member

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    The reason why a spinning wheel is heavier to turn is because of the gyro effect. Not because it is heavier. In fact the gyro effect is what makes it possible to ride bikes. Except for maybe trials riders.