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

[leviterande]

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 won't 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

 

[DrStupid]

There is no difference. It just looks different.

 

[leviterande]

There is no difference. It just looks different.

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

 

[DrStupid]

Do you mean that there is no difference between the two cases in the effort lifting the gyro?

Yes.

It is IMHO very clearly demonstrated that the lifting effort by Eric is widely different between the two cases.

IMHO it was his intention to created that impression in order to increase the show effect.

 

[leviterande]

Yes.
IMHO it was his intention to created that impression in order to increase the show effect.

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

 

[DaveC426913]

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.

 

[leviterande]

Yumpin' Yehosephat! How much kinetic energy is he holding there!

As for critiquing: he has the weight scale right there. Why doesn't he keep it attached, and show that the object actually weighs less!?

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

 

[DrStupid]

It felt a lot easier, just like it did with Laithwaite, the question is how.

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.

 

[zoki85]

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,

I was also surprised when I lifted 100 kg rock with a lever for a first time. But I was kid then, hehe;)

 

[DaveC426913]

Hello Dave, indeed:) I really hope however that you have read that I know that there is no weightloss during this maneuver

Yes. I understand that.

:) 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

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.

 

[CWatters]

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.

 

[leviterande]

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.

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 can't 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

 

[A.T.]

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,

The follow-up video explains why it seems lighter:

 

[Buckleymanor]

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.

 

[A.T.]

...the centre of mass shifts in effect to wherever you hold the giro apart from the spinning wheel...

Why would the gyro's centre of mass shift, just because it spins?

 

[Buckleymanor]

Why would the gyro's centre of mass shift, just because it spins?

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.

 

[jbriggs444]

That's the center of pressure, not the center of mass.

 

[nasu]

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.

 

[A.T.]

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.

That has nothing to do with shifting the center of mass.

 

[Buckleymanor]

That's the center of pressure, not the center of mass.

Could you explain.

 

[Buckleymanor]

That has nothing to do with shifting the center of mass.

Could you refute what I explained in a more tangeble way .If the centre of mass does not shift how come the giro does not fall over when it's spinning in a horizontal fashion on a stand or suspended from a string.It simply won't do to say it has nothing to do with the shifting of the centre of mass and then wait for someone else to explain .

 

[A.T.]

Could you refute what I explained in a more tangeble way .

http://en.wikipedia.org/wiki/Center_of_mass
In the case of a single rigid body, the center of mass is fixed in relation to the body

...how come the giro does not fall over when it's spinning in a horizontal fashion on a stand...

Because the torque from gravity (which is still the same as for non spinning) results in rotation around the vertical axis, not a horizontal one:
http://en.wikipedia.org/wiki/Gyroscope#Description_and_diagram

 

[jbriggs444]

That's the center of pressure, not the center of mass.

Could you explain.

You are working from the assumption that the [effective] center of mass defined as the place under which you have to support an object so that it does not fall over. The words you used were "center of mass shifts effectively".

For a non-rotating object, this behavior does hold. The center of mass will be located directly above (or below) the single point where you can support (or hang) an object in a stable fashion. But it does not amount to a definition of "center of mass".

For a spinning gyroscope you can support it anywhere. It will not "fall over". But if you fail to support it (or hang it) from a point directly under (or over) the center of mass, it will not be stable. It may not "fall over", but it will precess.

By "center of pressure", I mean to indicate the point where the support force is centered. You can find the center of mass defined in any number of references. Roughly speaking, it is the mean location of the component masses of an extended body.

 

[Buckleymanor]

If the behavior holds for non rotateing objects but not for ones that spin.How do we know that for spinning objects this is not what is happening.
What concerns is that it might be the case that centre of pressure has been substituted as a semantic explanation when experimental evidence shows that the centre of mass has shifted when compared with non rotateing objects.The center of mass could well be the mean location of the components masses but if it's spinning and rotateing on a stand or string does this still hold.

 

[jbriggs444]

Center of mass means what center of mass is defined to mean. It does not mean anything else.

 

[Buckleymanor]

http://en.wikipedia.org/wiki/Center_of_mass
In the case of a single rigid body, the center of mass is fixed in relation to the bodyBecause the torque from gravity (which is still the same as for non spinning) results in rotation around the vertical axis, not a horizontal one:
http://en.wikipedia.org/wiki/Gyroscope#Description_and_diagram

Thanks for the reply will have a good look at those links.

 

[A.T.]

The center of mass could well be the mean location of the components masses but if it's spinning and rotateing on a stand or string does this still hold.

Yes, a definition is always correct, per definition.

 

[jethomas3182]

It looks to me like the video A.T. provided explains it, in line with some of DaveC's comments.

When you tilt the rotor sideways, it precesses. One direction it precesses up, the other direction down.

If you turn it in the direction that it precesses up, it is easier to raise it -- you don't have to provide as much force upward. Maybe if you set things up right you don't have to provide any upward force at all beyond what it takes to hold it up. Because you are instead providing a sideways force that is getting transformed into an upward force.

 

[DrStupid]

a sideways force that is getting transformed into an upward force

... violates conservation of momentum

 

[Mesafarmer]

Torque=dL/dt
Notice that when he raises the wheel, it rotates in a circle about his body. The angular momentum of the wheel can be represented by an arrow directed out of the end of the axle. When the device is moved some small angle in the horizontal plane this arrow will shift in space. Do a little vector addition and you'll find a small horizontal vector must be added to the old to create the new one. Use you right hand to determine the meaning of this vector. It is a moment that acts along the shaft held by the professor. If you are holding a heavy object at the end of a beam it creates a moment that you must react with both hands. For instance, if the axle is two feet long and one hand is in the center and one at the end, the center hand will provide an upward force of 80 pounds while the outside hand pushes down with 40. When the wheel is spinning and changing direction a moment can be generated so that the person holding the device only has to provide the lift equal to the weight of the device. That is a huge difference in the perception of the lifter.

 

[jethomas3182]

a sideways force that is getting transformed into an upward force

"... violates conservation of momentum"

Oops. What's the right way to say that?

It creates a torque that tends to rotate the gyroscope at right angles to the direction of motion, that is, up. You don't notice the opposing torque on you as a weight on your arms.

Something like that?

 

[curiouschris]

No one here has answered the question. which makes me even more curious as to why it is easier to pick the weight up over his head.

Lets get a couple of things straight. there is obviously no cheating in the video's.

Regardless of how you hold the weight. it weighs 40Kg. The use of a lever amplifies the torque on the wrist many fold so while he can pick the weight up over his head when it is not spinning he can only do so by holding it as close to the weight as possible. If he attempted to do it from the end of the axle (lever) it is extremely doubtful he could do that.

When it is spinning he lifts it rather easily.

Now clearly he is lifting it in the direction it is precessing. My guess is he could not force it to go in the other direction and if he attempted that it would drive itself into the ground.

But the question remains. why is it easier to lift in the direction of precession and presumably harder the other way(yes that's an assumption).

Yes the spinning weight has much more potential energy due to its spin but how is that transferred in such a way as to make the lifting significantly easier?

Shouldn't it still weigh the same, and therefore require the same effort?

The answer stating the duration of time it takes to lift the weight is quite clearly wrong. this is not a block and tackle where the weight is supported by other means.

 

[jethomas3182]

Curiouschris, it is because the gyroscope is spinning.

Why does that change anything? He's holding the end of a long lever. If he tries to torque up or down, the gyroscope will move sideways. If he tries to torque sideways, the gyroscope will tilt up or down.

He tries to spin it around his head, and it resists that but it smoothly goes up. He isn't pushing it up, he's only holding it, but it goes up. He doesn't think about the sideways force he's applying because it's easy to do, and it isn't pushing up.

When he brings it down, first the scale sees the weight go down and then later it goes up. That happened only a little bit at a time when he was raising it.I think he thought it was easy because he didn't have to push it hard upward to make it go up. He didn't notice how hard he was pushing it sideways.

 

[hmmmok]

because as the mass of gravity approaches zero the mass in the centrifugal force equation increases to its max.

 

[Simon Bridge]

No one here has answered the question.

Yeah they have - A.T. provided a decent description in an earlier post.

... which makes me even more curious as to why it is easier to pick the weight up over his head.

The devil is in the details: he didn't "pick the weight up over his head", he gave it a shove to the side and then got out of it's way.
... it can take a bit to wrap you head around it though: Where did the description, in A.T.s post, lose you?

People who are still confused may need a bit of a primer:
http://hyperphysics.phy-astr.gsu.edu/hbase/gyr.html

... the key to the "effortless lift" effect is to understand about gyroscopic precession:

From there the discussion about how the precession leads to the ease (or otherwise) of lifting should be easier to understand.

Note:
The motion of the demonstrator should not be separated from the motion of the gyro.
Notice how none of the demonstrators tried to lift while turning the gryo against it's precession?
We cannot discount the human "impression" effect - esp. "effort" is subjective and poorly defined.

The interested student should analyse the forces and torques in the following situations:
1. Does holding the gyro in place require less effort while it is spinning than when it is not?
2. If the spinning gyro was not held totally in place, just holding it up, what would happen?
3. Is lifting the spinning gyro above the head without turning it (i.e. as a dead lift) easier than when you turn it as you lift it?
... note: these are guiding questions to help students.