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23 November 2024 15:27
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Question |
| Asked by: |
Lev |
| Subject: |
A question to Harry K. about Laithwaite´s 50lbs Gyro |
| Question: |
Hi all!
I have been looking for answer for this seemingly simple but important point without success at all.
As you all know, the "in"famous demo here:
https://www.youtube.com/watch?v=MHlAJ7vySC8
the same thing here:
http://www.youtube.com/watch?v=GeyDf4ooPdo&src_vid=tLMpdBjA2SU&feature=iv&annotation_id=annotation_3902025237
I am aware that the gyros fully follow Newtons laws.
Gyros have Centrifugal forces just like everything else unlike Laithwate´s sayings.
Gyros can be held at a very large distances from the c.g of the spinning mass just simply because of the TORQUE that is introduced as the gyro precesses, so no problem here holding a 50lbs or any other gyro - from the end point of a 3ft shaft.
So, we can assume that Laithwaite lifted the gyro both times in both the spinning and non spinning state essentially really at the "center of gravity ":
However , there is one point that I cant figure it out:
How come he had a much much harder time "LIFTING" the gyro upwards when it was not spinning.
Keeping in mind that he lifted basically the gyro both times at the effective C.G.
To put it clearer :
1-When it was not spinning: used two hands, much closer to torso for much bigger mechanical advantage, was struggling to lift, didnt lift it high.
2-When it was spinning:used one hand, much further from torso which is worse mechanical disadvantage and lifted it much higher and with far less effort.
What is the reason of this tangible observation?
Regards |
| Date: |
3 November 2014
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Answers (Ordered by Date)
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| Answer: |
MD - 04/11/2014 01:27:30
| | | When the gyro was spinning it also stabilized the whole rig, that is, the shaft and the metal disc.
When it wasn't spinning he had to use a lot more muscle force to keep it stabilized. If you want an accurate comparison, try going to a gym and bench press a 40 pound weight. You might not make it. Then move over to a machine where the weight is on a rail. Then you might make it.
It's actually the same weight, but because the machine is on a rail you can ignore all balancing issues and just push.
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| Answer: |
Lev - 04/11/2014 22:39:52
| | | MD; thanks and I agree. Absolutely a valid point, very true, It is indeed easier to lift a stabilized weight. The question is though : is this the only full answer to why you could lift that gyro so much easier upward? could there be other things too? Even though stabilizing makes it easier to lift. it feels as it was so much of a difference in the two videos. Perhaps really that is though all there is..
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| Answer: |
Harry K. - 05/11/2014 00:03:44
| | | Hello Lev,
This example describes the difference between force and torque pretty well. The spinning wheel deflects the vertical acting torque, created by its weight x lever arm length, into a 90° horizontal torque with same size. The weight of the wheel will act directly in the center of horizontal rotation, assumed the person will assist this rotation by giving the degree of freedom. If the person increases this rotation speed, the spinning wheel will move upwards. These effects make it much easier to move a spinning wheel upwards as it would be if the wheel would not spin.
This is a nice demonstration, however, there is no energy saving festure achievable.
Anyway, under certain conditions, there could be indeed a loss of weight. But this is another issue and in the moment I will not explain why it could be. Maybe later... ;-)
Kind regards,
Harald
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| Answer: |
Lev - 05/11/2014 07:40:29
| | | Harry K. thanks. What you described is gyroscopic precession. If you don´t mind, I want to say that thus, I don´t understand how :
"These effects make it much easier to move a spinning wheel upwards as it would be if the wheel would not spin."
Now, how exactly do "these effects" -as you said- make it easier to lift? Only thing I can see is the stabilization effect due to all the spinning, are stabilization "effects" what you meant in the above quote?.
However, my point is if the "ease of lifting" is really just 100% due to simple stabilization of the mass lifted or.., if there is something more going on here? So,pardon me for my slow mind, but would you elaborate on how you meant that these effects(precession) makes it easier to lift? or, perhaps you simply just meant the stabilization effects?
Regards
Lev
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| Answer: |
Harry K. - 05/11/2014 09:47:07
| | | Hello Lev,
Yes, I described gyroscopic precession of an overhanging bedded gyroscope / spinning flywheel.
In this case the weight of the spinning flywheel as well as the dead weight of all other involved parts, e.g. lever arm, cages, etc., will cause a downward torque. The size of this downward torque can be calculated by the product of the wheel mass and the lever arm length (other involved dead weight masses are unconsidered). The lever arm length is the distance from the center of spinning mass to the fulcrum (e.g. shoulder joint of the person or the center of mass of the person).
Due to the spinning mass, this created vertical torque will be deflected about 90° into horizontal plane, i.e. the spinning flywheel will not move downward as expected but begins instead to rotate around the same fulcrum but in horizontal plane what is called precession movement. The direction of rotation in horizontal plane depends on the spinning direction of the flywheel. The size of the deflected horizontal torque is identical to the size of vertical torque, created by gravity and lever arm length. The speed of precession movement depends on the mass of the flywheel, lever arm length, spin speed and flywheel diameter and its shape (hope I did not lost something).
The vertical torque created by gravity will change the spinning path direction of each involved mass particle and cause additional angular momentum rectangular to the actual spinning path of the mass particles. The particles spinning on the top most position (12 o´clock) and the lower most position (6 o´clock) are under the most influence of the acting torque. The torque influence increases in a sinusoidal form from zero at position 3 and 9 o´clock to the maximum at position 6 and 12 o´clock. That means the upper and lower half sections of the flywheels are under the influence of the vertical torque, which tries to rotate the both sections around its center of mass. However, the flywheel can only draw aside in horizontal plane. It is important to know that the spinning flywheel always react from its center of spinning mass. Based on the given degrees of freedom the reaction torques will be transferred to other spatial positions given by the degree of freedom. However, the size of the transferred torques will not be influenced and will be always equal.
The now in horizontal plane precessing flywheel will cause in return a counter torque to the vertical acting torque caused by gravity. The procedure to cause this counter torque is identical to the above description with the exception that the left and right half sectors are now involved to create the counter torque. This counter torque cancels out the weight of the spinning flywheel due to its force vector in vertical upward direction and exerts its force vector in vertical downward position thru the fulcrum. Both force vectors have the same size and thus the weight of the flywheel will be transferred to the fulcrum during precession movement. This is my answer you asked for.
If the precession movement will be increased (what requires physical work) the flywheel will move upwards around the fulcrum (the lifting work is equal to the additional work in precession).
If the precession movement will be restrained in any form, the flywheel will move downwards around the fulcrum. The balance of energy will always be unchanged.
It SEEMS to be easier to move a spinning flywheel upwards because the weight of the flywheel is directly transferred to the fulcrum. To move a non spinning mass upwards, always a torque will be created because it is not possible to move the flywheel upwards directly in its center of mass for anatomical reasons. If it anyway could be possible, you would not notice any differences if the flywheel is spinning or not.
Hope this helps a bit in understanding.
Regards,
Harald
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| Answer: |
Lev - 05/11/2014 11:48:18
| | | Hi again Harry K.
I Appreciate your time and help.
Lets just be clear that we are talking about the same point here.
You said:
"It SEEMS to be easier to move a spinning flywheel upwards because the weight of the flywheel is directly transferred to the fulcrum. To move a non spinning mass upwards, always a torque will be created because it is not possible to move the flywheel upwards directly in its center of mass for anatomical reasons. If it anyway could be possible, you would not notice any differences if the flywheel is spinning or not"
On the risk of being too over-analytic, I would love to make it clear that I am not talking about the superficial "seemingly magical effect" of how you can lift the gyro from its very far end of the shaft, which is of course is a very well simple known fact as you have elegantly explained. Laithwaite tried to lift the gyro both times (in the spin and non-spin states)
"from the center of mass" right? or?. He lifted the spinninggyro and it was effortless. Yet, when he lifted the non spinning gyro with a scale first, it was so much harder, even with 2 hands.
Hmm, wait a second, I may possibly catch your drift now.., are you saying that, when he tried to lift the non-spinning gyro from that HANGING SPRING SCALE with two hands, that he still didn't- and no one would- actually lift it at the center of mass either because..,
-as you said- "it is not possible to move the flywheel upwards directly in its center of mass for anatomical reasons" .
Am I understanding you correctly here Harry? Is your last mentioned quote correctly and rightfully being applied to the case of Eric lifting with the spring-scale or me lifting a stationary weight hanging from a rope etc..?
Regards
Lev
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| Answer: |
Harry K. - 05/11/2014 13:36:21
| | | Hello again Lev,
Or should I call you Dr. Fisher or Stan Smith? Is there again a semester break?
My explanations were referring on the experiment itself but not on the weighing procedure with the hanging spring scale. Certainly you can move the flywheel, spinning or not, in its center of mass by the use of a rope or a spring scale but not in the case if you try to lift it with your arms. I’m pretty sure you are aware about these facts. Or maybe not? – I do not care.
Have fun,
Harald
P.S. This was my last response
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| Answer: |
Nitro - 05/11/2014 19:19:02
| | | Dear Lev,
I don’t think you could possibly be the infamous Dr David Fisher as Harry suggests so I will put in my two penny worth. The Laithwaite video you linked to is, as usual, all to do with Nitro’s first law, which states that “a gyro will precess every force applied to change its axial angle, not just the ones you happen to have thought of!”
Harry is right in describing that when the gyro is released to allow gravity to try and change its axial angle the gyro happily precesses that force applied to change its axial angle into a rotation around Laithwaite. Laithwaite only needs to act as a fulcrum to support the gyros weight at the end of the shaft. When the gyro is not spinning the leverage of the long shaft would obviously make this impossible. With precession, as the rotation of the gyro around Laithwaite is being provided by precessed gravity, any small additional torsional force applied by Laithwaite in the direction of the initial, gravity caused, precession must cause the gyro to precess this new applied force and the gyro has to move upwards.
While I happily acknowledge Laithwaite’s genius I don’t think it is necessary to blindly bow to him and his views as if he were a god (He had some self promoting habits – don’t we all?) but I am relaxed in saying that the first and third laws are, at the very least, in need of modification.
Simples
Kind regards
Nitro
PS While I happily acknowledge Newton’s genius I don’t think it is necessary to blindly bow to him and his views as if he were a god (He had some very ungodly habits – don’t we all?) and I am relaxed in saying that the first and third laws are, at the very least, in need of modification.
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| Answer: |
Lev - 05/11/2014 19:30:12
| | | HI, Ok, it seems that there is some misunderstanding. And, semester break? Dr Fisher? I honestly and truly dont get your point. At any rate I am sorry if you felt offended in any way, I never meant to offend anyone. I was as I said over analyzing just to avoid this misunderstanding. Ironically the opposite apparently happened. My fault..
I am aware of these facts you mentioned. And I asked to be more sure if we are talking about the same details.
All I wanted to know is how Eric laithwaite had a much much harder time lifting it from the spring scale(which is C.M), whereas the gyro became light as a feather when it was spinning. He was lifting both times essentially directly at the center of mass(spring scale on stationary gyro) as I initially thought/wrote and as we agree.
You explained that it only "seems" easier to lift because the weight is transferred to the fulcrum. Correct, but, however, when laithwaite tried to lift the stationary gyro from a spring (which is essentially a rope directly at the C.M), it was still so much harder. So why was it easier when he gyro was spinning?.., why easier when the gyro was being lifted directly at the C.M in both cases..( stationary gyro with spring scale/rope vs spinning gyro).
Dear Harry, you do as you please. I only wanted as I said to get an answer for this issue. This question is ofcourse open to anyone. MD stated the stability effect of being the cause which I am aware of . But is it all the cause specially when the stationary gyro was indeed also lifted directly at the CM by the "rope"?
Wish you the best.
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Lev - 05/11/2014 19:43:03
| | | Oh, I just read Nitro´s comment.. oh it looks like I have been misunderstood at several levels.
Nitro I get your point but it seems you didnt get mine :). ha?
I am not referring to the shaft, and how a gyro can be supported at the far end.... To put my point in one final way as can be seen from the video:
1-Attach a gyro to a rope, lift it from the rope and it is going to be very very hard to lift up even with both hands(as seen in video).
2-Spin the gyro and make it precess(a la Laithwaite style in video) while lifting it up and the gyro becomes very easy to lift up with one hand.
I am not sure if this can be made clearer than this.
I am not reffering to antigravity, free energy or such things. How and what is the explanation. is what I seek.
Thanks
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| Answer: |
Harry K. - 05/11/2014 21:50:16
| | | Hello Lev,
Sorry, it seems I mistook you with a very special guy...
I watched again both videos but could not find the point were the flywheel / gyro were lifted from a rope. I could only find the point were the flywheel was lifted from that hanging spring scale with both hands. You can clearly see in the video that Laithwaite has to lift the flywheel with his forearms around the pivot of his ellbows. That means a torque will be created and thus it is a harder for him to hold the flywheel at ist position.
During the lift of the spinning flywheel, the flywheel rotates around the pivot of Laithwaite shoulder joint and thus no downward torque will be created and this makes it much easier for him to lift the flywheel upwards. If Laithwaite would not assist or would block the horizontal precessing movement, the flywheel would merciless try to rotate the Professor around his center of mass and would simultaneously move downwards with precession speed. He would not have any chance to move the flywheel upwards if he would not assist that movement in precession direction.
Is this so hard for you to imagine or understand? For me you do not give the impression that you do not understand pretty well the beavior of a flywheel / gyro under the influence of impressed forces.
Regards,
Harald
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| Answer: |
Lev - 06/11/2014 08:07:35
| | | Hi Harry, I analysed the motions of the gyros and the Laithwaite´s gyro. I built several physical gyros just for that- to see the forces, force reactions in 3d, filmed the reactions with slow motion, in all directions, I even built a mechanical model of the Laithwaite Gyro demo video, where I made 3 mechanical pivots instead of shoulder, elbow and wrist. I thought this should also visually show and explain easily the whole procedure. And then.., something was somehow off.
But Aaah, I think now, the knot in my brain has been untangled,thanks to your referring to "shoulder". You see, I analysed the motions and forces in all directions and built a model of Laithwaite´s full arm. Everything was correct except one tiny bit that screwed it for me, it apparently got overseen during all the work.
The mechanical "wrist" of the physical model was loose and free to pivot. While the human wrist is indeed free to pivot it is also easily made not to. That is apparently the root of the problem. You see, if the wrist is free, the gyro will torque about that wrist axis and leave the elbow and shoulder still stationary and hanging down. If the wrist is locked or even slightly attached/rigidly to the elbow, the torque would be transferred to the elbow and thus again to the shoulder.
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| Answer: |
Harry K. - 06/11/2014 08:45:27
| | | Hi Lev,
Glad to read that you could find the solution for this issue. It’s a platitude that effective forces / torques will always take the path of least resistance in a system.
Regards,
Harald
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| Answer: |
zawy - 26/08/2015 23:38:58
| | | Here is my video demonstrating the "laithwaite effect". Bascially, it is easier to lift because the wrist can add a twisting force to assist the triceps, plus the initial acceleration he tosses into it.
https://youtu.be/YxhZ199AMDQ
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Sandy - 28/08/2015 19:55:29
| | | Zawy
It would be better if you and Lev, tried the experiment with a 50 lb wheel,
Sandy
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