9.06.2020

The "Anti-gravity" Wheel by Veritasium explained correctly

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 Here are the video's:

anti gravity wheel

Explanation (incomplete):

 

So what is really going on here?

Notice that if you lift something (non spinning) on a scale, the scale weight goes up while you are lifting it. Why?  Because something "gets heavier" when you are accelerating it.  This is because it takes a force to counter gravity and an additional force to accelerate something.  Now when you have the body spinning (in the right direction!) you can use some of that rotational energy (by thrusting it the right way as said in the explanation video) to make it so you do not need to exert that extra upwards force to accelerate it.  You sap some of the rotation (the spinning wheel slows down a bit) and use that energy to accelerate the body upwards without using an upward force to achieve it (you do use some horizontal force in the thrusting outwards).  Basically another way to look at it is the spinning wheel is a machine that converts horizontal force into vertical force.  

Now if you try to move the wheel in the opposite way it gets heavier!  Why is this?  Because your "horizontal thrusting force" instead of sapping energy from the wheel to negate force needed to accelerate it, you are adding energy to the rotation of the wheel instead of lifting it!  So it feels even heavier (and the scale would actually go up as you lift) since the force you are creating is getting sucked into the wheels rotation instead of taking energy out of the wheels rotation, during lifting.

In conclusion the spinning wheel is just a quite complex system which is why the reasoning for why it makes things "feel" the way they do is obfuscated behind multiple layers of complexity.  The conclusion is that lifting a weight the proper way that is spinning actually requires less external force than lifting it not spinning.  This is because you are using up some of the rotational energy of the weight to accelerate it upwards.

4 comments:

  1. A couple of engineers discussing this. I suggest that you are looking in the right area, but making an error. As you seem to say, it takes a force greater than the weight to lift something. You need to supply the F=MA force in addition to the weight.
    Gyros do not convert a torque to a linear force. They convert a torque to another torque in the direction 90 degrees "later" in the rotation.

    When you force the precession faster (with left hand) and the gyro "rises", it is not really rising against gravity, but precessing. That is, it is changing its axis of rotation to a direction 90 degrees from the direction your push is trying to change the axis.
    I haven't worked out the detail because you are not only forcing the precession to be faster, but also raising your right hand and, therefore applying two forces/torques.
    I initially speculated that the result is that a net torque caused by the gyro is in the direction to lift your hand so you never see any more than the 40 pounds of the dead weight of gyro + shaft during acceleration.

    The left (precession forcing) hand must be providing assistance to the right lifting hand, thus giving the right hand less work to do.
    Unfortunately, the left hand seems to translates to a linear force accelerating the gyro's weight upward, which still sounds wrong.
    .
    Regards

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    Replies
    1. Thanks for that. That seems like an even better explanation. Yes, the exact science is a bit hazy hence why I used vague terms, but the basic premise holds, you are using up rotational kinetic energy of the rotating disc, with artistic hand movements, to supply the force to lift the object; instead of only the normal force on the ground counteracting the weight and also providing the upwards accelerating force.

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    2. Well, I'll claim it isn't vague if you are able to consider all the required fundamental principles of physics. Some of these things are not what we normally study, like the forcing of the precession and it's effect. But se know about this 90 degree change in the direction of the force and can reason out what that does.

      One thing it does do is to make your hand location the same as holding the wheel and bar at its center pf mass. We know this because there is no torque applied to your hand. You feel like you have a small 40 pound weight in your hand and are lifting it. There is no sensation of a long arm with a weight on the end.
      It is an interesting phenomenon.
      Cheers

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