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Why is it so much easier to lift a spinning gyro than if stationary?

  1. Nov 5, 2014 #1
    Hi all,

    First of all, I just want to make it very clear that I am not referring nor meaning toward antigravity , free energy or such nonsense subjects. Eric laithwaite had a lot of misunderstanding about the gyro behavior that can be explained with Newtons laws. I just really want to understand one other point. I am also aware of how gyroscopes behave: all properties can be explained simply and shortly due to the good old conservation of angular momentum.

    NOTE: Please, to avoid unnecessary misunderstandings, my question is not referring to the superficially and naively "magical" effect of lifting a gyro from its 3ft shaft end. I understand that, we are dealing with simple torque which is again due tue conservation of angular momentum.

    I tried to ask about the following VERY SEEMINGLY SIMPLE OBSERVATION to a lot of people and I couldn't get any answer. You are my only last hope:

    Watch Eric Laithwaite´s infamous video:

    1-First, at 0:45 The gyro is lifted directly at the Center of Mass with a (springscale or a rope) and is very hard to lift, with both hands, closer to torso (bigger mechanical advantage) and reaching a low height.

    2-Secondly, at 2:54 The same gyro is spun and as it is precessed (and of course torqued upwards all obeying the laws), the gyro is lifted (at also essentially the C.o.M too ) with one hand to a much greater height with a far less effort.

    What we saw is that the total effort to lifting the gyro in the two cases differed very markedly.

    How, why? What is the reason it is that so much easier to lift the gyro in the latter case? That, despite the fact that the gyro was essentially lifted both times, both cases directly at its Center of mass?( i.e.with the spring-scale/rope when not spinning and at fulcrum when it was spinning case)


    Own Thoughts, possibilities Cause(?):
    Just simply gyro spin-induced stabilization. Gyroscopic inherent tendency to stop any torquing of the C.o.M makes it easier to lift up any mass since you wont need to fight any torques otherwise induced when trying to lift a stationary mass where the C.o.M would be constantly free to flip all around over the place?

    Objection to this cause(?)
    Sure, absolutely, gyroscopic/spinning stabilization makes it easier to lift, We all know the free weight dumbbells vs machine at the gym examples...
    But, shouldn't the rope/springscale attached to the stationary gyro at 0:45 also automatically and constantly lift this non spinning gyro directly from the C.o.M, stop any torquing of the C.o.M and thus, you also wouldn't need to fight any destabilizing torques? Then why is it much harder lifting from the rope than with the gyro spinning & precessing.

    I really tried to be as clear as possible,
    I hope you get my point.

    Thanks a lot for your time. Again I am here to learn
     
    Last edited: Nov 5, 2014
  2. jcsd
  3. Nov 5, 2014 #2
    There is no difference. It just looks different.
     
  4. Nov 5, 2014 #3
    Do you mean that there is no difference between the two cases in the effort lifting the gyro? It is IMHO very clearly demonstrated that the lifting effort by Eric is widely different between the two cases.

    Thanks
     
  5. Nov 5, 2014 #4
    Yes.

    IMHO it was his intention to created that impression in order to increase the show effect.
     
  6. Nov 5, 2014 #5
    Thanks for the reply.I see your point.
    It seems though that Eric wasn´t the only one who felt this big difference . Veritasium the science guy on youtube replicated this effect and indeed he was also very surprised how light it felt to lift when it was spinning,


    At 1:49 you can even hear his shoulders "pop" as he struggles to lift the stationary gyro first, with his back also arched which gives better mechanical advantage. Still he can barely lift it high.
    At 2:47 As it is spun, he got very surprised how easily he could lift it as he said himself and even got it to a higher altitude., with his hand out from torso which is a very bad mechanical advantage from his body point of view..He is of course not lying. It felt a lot easier, just like it did with Laithwaite, the question is how. With all due respect I suspect that indeed it feels a lot easier to lift a precessing gyro did for some reason. Now, please don´t get me wrong, I am of course not referring to weight-loss since there is no weightloss going on here at all.
    It is the reason behind the superior ease of lifting, that I want to know.

    Thanks
     
  7. Nov 5, 2014 #6

    DaveC426913

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    He has the weight scale right there. Why doesn't he keep it attached, and show if the object actually weighs less!?

    I would point out that he is essentially rolling the object up a long hill. He raises it 5 feet over a distance of about 10 feet or more. He's employing a mechanical advantage.

    It may seem like he's using less effort, but that's because you're only witnessing the vertical effort - which is spread over a long time and distance. You are ignoring the horizontal effort.

    I can lift a hundred pound mass 5 feet in the air with one finger - if I use a 6:1 block and tackle. Of course, you might not notice that I've pulled in 30 feet of rope, not merely 5 feet.


    And finally, so what if it did require less effort from him? The thing has been imbued with a huge amount of energy, from which it can - as he points out - lift itself 200 feet in the air, if he wielded it correctly.

    He's converting energy - that the object has been given - into motion. Why is this counter-intuitive? If it had propellor-blades on it, would you be surprised if it was easier to lift when spun? No.
     
    Last edited: Nov 5, 2014
  8. Nov 5, 2014 #7
    Hello Dave, indeed:) I really hope however that you have read that I know that there is no weightloss during this maneuver :) Poor Laithwaite as we know made many errors such as gyro not having centrifugal forces etc. This is not the point of my post. My point was outlined in my earlier posts in which I am still really trying to find an answer to. Thanks
     
  9. Nov 5, 2014 #8
    If it really felt easier it is a psychological effect. The force needed to hold the gyro in this position is less than expected. But it is in fact identical with the non rotating gyro. There is a similar effect in case of objects with equal mass but different size.
     
  10. Nov 5, 2014 #9
    I was also surprised when I lifted 100 kg rock with a lever for a first time. But I was kid then, hehe;)
     
  11. Nov 5, 2014 #10

    DaveC426913

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    Yes. I understand that.

    Perhaps then I did misunderstand. I thought you were wanting to understand how it is that - knowing no strange anti-gravity effects are being demonstrated here - it still seems as if it requires much less effort to lift when spun-up.
     
  12. Nov 5, 2014 #11

    CWatters

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    In his infamous Christmas lecture a small boy lifted a heavy gyro. Watch from about 5 mins in...



    Clearly the combined weight of boy and gyro is the same in the spinning and stationary case BUT nevertheless the boy does find it easy to lift when spinning. This shouldn't be a surprise. Note they aren't simply lifting it, they are trying to stop it rotating when they lift it with both hands at the far end of a long shaft.

    Aside: Yes I know two different boys were used but still.

    Edit: This goes to the heart of his mistake. He thought gyros could produce linear forces when in reality they produce torques.
     
    Last edited: Nov 5, 2014
  13. Nov 6, 2014 #12

    Hi Dave, Thanks for your previous explanation. About the last part of post #10, I am not sure if this discussion could be in danger of being tangled :), but it seems so far that you understand my point perfectly. So yep, we both here agree that Laithwaite made the mistakes and we both agree there is no gravity effects and thus all I want to know is simply how it "is" or it "seems" much easier to lift., hence my opening question.

    So to get back on the subject, and your analogy in post #6.
    Considering your idea, yes I understand it well, at first sight, perfect logic, in fact that was the very first thing that hit me when I saw the videos for the first time. But I originally disregarded this idea because I cant grasp:

    How would the mechanical pulley/ramp analogy be applied to a precessing gyroscope in the "free air"?

    You can roll a ball up a 5 degree incline with ease for a long period of time to get to a specific height. You can use the same energy to roll the same ball up to the same height in much shorter time but with far greater effort because of the much deeper incline. How can this analogy be applied to the seemingly "free gyro"? How can the gyro "gear" itself up without being supported on some solid mass. Where is the "ramp" that the gyro is supposedly climbing upon.
    Mechanical analogy= You+Ball+Ramp
    Gyro demonstration =You+Gyro-------where is the alternative to the ramp?(or more correctly, how can this be explained in the gyro?)
    Of course. I don´t literally mean the ramp here but just trying to make a point.

    Interesting, this subject is. I heard two other(non nonsense) explanations for the subject as well but will save that for another time.

    Thanks for your time
    Regards
     
  14. Nov 6, 2014 #13

    A.T.

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    The follow-up video explains why it seems lighter:

     
  15. Nov 6, 2014 #14
    It's easier to lift because the centre of mass shifts in effect to wherever you hold the giro apart from the spinning wheel.The total weight remains the same when spinning but the shift in centre of mass allows the wheel to be lifted without gravity creating a downwards torque as it would when it is not spinning.
     
  16. Nov 6, 2014 #15

    A.T.

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    Why would the gyro's centre of mass shift, just because it spins?
     
  17. Nov 6, 2014 #16
    I am not sure but you can measure the effect.If you take a spinning giro, place one end of it on a stand and make sure the giro is rotateing horizontally then weigh it with the stand on the scale.The giro will weigh at the point of contact the total mass of giro pluss stand.You can the do the same at the other end or any point where it is not spinning and you will get the same result.If it was not spinning it would fall over.
     
  18. Nov 6, 2014 #17

    jbriggs444

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    That's the center of pressure, not the center of mass.
     
  19. Nov 6, 2014 #18
    The effort for lifting something depends a lot on the position of the arms.
    He is lifting the non-spinning system in a very awkward position, bending his arms from elbows. And this because he holds it in a vertical position and then adds the scale, so the whole thing is almost as tall as he is. So he is more like pushing it up.
    If you ever tried to weight a tall suitcase you would know that it is not a good position for lifting something.
    The spinning system is held in a completely different position of the arms. He is pulling it, using mostly the shoulders articulations rather than elbows and having his arms extended.

    If you have two suitcases of the same weight, but one very tall and one that you just bend you knees a little to grab, the efforts to lift them and to hold them will be different. But this is an effect of the mechanics of the human body, not some special properties of the suitcases.
     
  20. Nov 7, 2014 #19

    A.T.

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    That has nothing to do with shifting the center of mass.
     
  21. Nov 7, 2014 #20
    Could you explain.
     
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