# Anti-gravity wheel?

So I was just watching some YouTube videos on a spinning wheel that seemed to "defy" gravity. The creator made two videos on it, the first showing the wheel, and the second with an attempt to explain it. There are the names of the videos:

"Anti-Gravity Wheel?" by Veritasium

"Anti-Gravity Wheel Explained" by Veritasium

It is the second video in particular that bothers me. It seems as if he can lift the wheel up over his head while it's spinning and precessing with ease, but when it's not spinning nor precessing, then he struggles to lift the weight over his head. He explains this as somehow the wheel "lifting itself" up as he forces it to precess faster than it's natural precession. But I don't really understand this explanation. To me, it seems as if it violates Newton's second law, which states that the total external force on a system (the wheel in this case) is equal to the total mass times the acceleration of the center of mass. Now, the center of mass of the wheel clearly goes upwards, meaning that an external force has to lift it. Therefore, the wheel can't lift "itself", for that is no external force, just internal forces.

I thought the phenomenon happened because of the Magnus force (an external force). That would also explain why his total weight didn't change much as the wheel got lifted up. But that is clearly not the explanation given in the video. So what is the right explanation for this phenomenon?

I agree that the attempt at explanation offered by Veritasium (Derek Muller) is unconvincing.

Now, it is not straightforward to make the motion of lifting the non-spinning wheel the same as lifting the spinning wheel. In the case of the spinning wheel the rate of precession is a given, that dictates the rythm of the lift. Derek keeps his feet on the ground, he is not moving his body to match the orientation of the bar, so the weight shifts over the muscle group of his shoulder as he goes through the lift.

Indeed the force required to lift the spinning wheel must be the same as the force required to lift the non-spinning wheel.

(Experimental verification of that is actually rather tricky. I've seen a video of someone who created a tabletop setup, with normal gyroscope. His measurement reading swung up and down a bit, he had to average. Derek tries it with that giant wheel, but the setup he uses isn't stable enough.)

Anyway, my best guess is that in lifting the spinning wheel Derek's arm is moving relative to his body, shifting the load from muscle to muscle, whereas in the other lift he is just killing one particular muscle. He really should have tried to replicate that flow of motion with a barbell for one-handed lift.

I just tried it with a barbell for one-handed lift. Lifting with my right arm I maintained a clockwise rotation of the barbell. Lifting the barbell was doable that way. Then I tried lifting with my arm at a fixed angle to my body. That was significantly harder. My best guess: at different horizontal angles to your body your upper arm has a different vertical angle of optimal leverage. Presumably that depends on the placements of muscle attachments. Apparently it so happens that the rotation takes a path where all along the lift you have good leverage. Conversely, if you try to lift with your arm at a constant horizontal angle to your body you will inevitably hit a vertical angle with poor leverage.

Derek Muller mentions: if you have a gyroscope wheel with the spin axis in the horizontal plane (hence you get a torque from gravity), then when you push to give the wheel a surplus above the natural precessing motion the wheel will climb. (Conversely, when you push against the natural precessing motion the wheel will descend.) Derek offers that as a possible explanation for why it feels to hem that lifting the spinning wheel is less hard.

This suggested explanation doesn't work. The reason for that: at the very instant you stop pushing this happens: the precession rate of the wheel goes back to the natural precession rate. Also, if Derek would not push at all, if he would simply release gingerly the wheel will go into the natural precession rate on its own.

In all: Derek's pushing arm can assist the lifting arm a little, but that assistence ceases when the pushing arm releases. At that point the wheel is still below the level of Derek's elbows.

Incidentally, this error doesn't stand on its own There is another video by Derek about gyroscopic precession with an error.

Video about gyroscopic precession 2:47 into the video

what happens if I only let go after I've already spun up the bicycle wheel well in that case the bicycle wheel would already have angular momentum this way and so a torque pushing that way actually swings this angular momentum round that way

(To avoid misunderstanding: Derek isn't the only one to make this claim; the claim does not originate with him.)

The suggestion is that the torque from gravity is being redirected, causing a precession instead of downward acceleration. The problem is: if that would be the case then the precession would speed up; a sustained force causes acceleration. But as we know: given a particular spin rate of the wheel, and a particular torque, there is a corresponding constant rate of precession. So: the suggestion that the torque from gravity is being redirected violates the laws of motion.

For a discussion of the mechanics of gyroscopic precession see my 2012 answer, the question is titled: What determines the direction of precession of a gyroscope?

• That seems reasonable, but the only problem I have is that the weight fluctuates up and down, and I don't see how that could be if it was him and him only who lifted the weight. I can see why the reading should change a little bit, as the acceleration of the center of mass of him and the wheel might not be uniform during the lifting (resulting in a change in the reading), but that reading was fluctuating very violently up and down, which seemed a bit "too much". Commented Aug 15, 2020 at 10:10
• @FelisSuper In my opinion the fluctuations of the indicator of that weighing scale are no grounds for doubt. Derek has to hold his balence while a 19 kg weight is moving relative to his own center of mass. That means Derek has to shift weight from foot to foot, and from heel to toe all the time; I think the fluctuations are fully accounted for. Commented Aug 15, 2020 at 10:20
• Yes, but the scale doesn't measure the force from an individual foot or toe or heel; it measures the total force that is being applied on it. And the extra weight on the scale must be exactly equal to the vertical acceleration of the center of mass of him and the wheel, times their total mass (Newton's second law) if there's no other external force. Commented Aug 15, 2020 at 10:27
• Not sure if you saw my last comment here, just adding @ Cleonis if that's the reason. Commented Aug 15, 2020 at 13:52
• By the way, I still can't see how the weight seemed to "lift itself". Derek described it as if it "wanted" to go up, meaning he barely had to do anything to help out. If it was him that did all the job, then I don't see how this could be. Commented Aug 15, 2020 at 13:55

This doesn't violate Newton's second law.

Lifting the wheel over his head by holding it on the end of a long handle is hard because of torque (imagine lifting a broom holding it in the middle of the handle compared to just at the end of the handle). If he had been holding the wheel-handle arrangement at its center of mass, he would have just as easy a time lifting it over his head as in the video! The effect in the video is just due to precession; atmospheric effects do not matter here.

The right explanation for this phenomenon is not the magnus effect because it is much to heavy. No the real cause of this is that flywheel momentum is being changed from mostly moving down to moving to its sides. This makes it a tad bit lighter Sense the momentum of the object is being used to conserve its angular velocity.

• Greetings! Please see this guidance on writing good answers. In its current form (v1), your answer is decorated with some unnecessary chit-chat. Furthermore your explanation about momentum is somewhat unclear; are you referring to linear or angular momentum?
– rob
Commented Oct 13, 2021 at 0:08
• I will fix my explanation thx for telling me. However i do believe the chit chat poses a good role in explaining the answer a bit more so i wouldn't change it too much. As for the angular momentum thing i have no idea. I do know that the rotation of the flywheel causes the direction of the force that is being applied to it (via gravity) change direction from down wards to... Hmm well i mean it is its sides right, or does angular momentum just mean spin. Commented Oct 13, 2021 at 0:23
• oh come on whats wrong with it that it deserves a down vote i mean i did make the changes you specified. Its not like i need an entire essay just to get a point across Commented Oct 13, 2021 at 1:00