
#19
Jan613, 02:56 PM

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P: 244

I will use a more simple example.
I have a modified powerball that is fixed to a concrete floor. Assume that I can turn the flywheel in it perpendicular to the flywheels rotation. Initially the flywheel does not spin. It starts to spin only when I turn it perpendiculary. If I stop turning it, its spin also stop. A gear mechanism makes sure of this. So, the flywheel will under all circumstances spin in the vertical plane, and at the same time can turn in the horizontal plane  without exceptions. I assume I will feel a counterforce as soon as I try to turn the flywheel perpendicular to its rotation, since the flywheel at the same time starts to spin perpendicular to the turn. Is that correct? Say the flywheel is spinning constant at 10 000 rpm. And it turns around perpendiculary at a constant 60 rpm. If I successfully maintan this constant cycle over time, would that also mean that I have to apply energy to sustain the rpm in the vertical and horizontal plane except for making up for friction? Vidar 



#20
Jan613, 04:41 PM

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#21
Jan613, 05:51 PM

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P: 244

Therfor I guess I must do work while turning the gyro around perpendicular to its rotation. (Suppose it is the same as fighting agains the angular momentum  applying energy to do so) 2. Which torques lead to what changes in angular momentum, and which do work, and why? Not really sure where you're heading with these questions. Vidar 



#22
Jan613, 07:57 PM

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Use this page as a reference http://en.wikipedia.org/wiki/Torque Especially the section on The relation to angular momentum and the section on The relation between torque power and Energy Other sources are http://en.wikiversity.org/wiki/Torqu...r_acceleration And http://bolvan.ph.utexas.edu/~vadim/C...11s/linang.pdf http://www2.cose.isu.edu/~hackmart/torque.pdf 



#23
Jan613, 09:41 PM

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Try to analyze it on your own first, but here are some hints.
Spoiler
Assuming a very high gear ratio we can assume that the angular momentum, L, is almost entirely along the axis of the gyroscope. The gearing makes it so that L precesses slowly about a circle. Since L is changing that means that there is a torque according to [itex]\tau=\frac{dL}{dt}[/itex].
If L is precessing in a horizontal plane then τ is also in the horizontal plane, but 90° "ahead" of L. So τ tends to make L rotate vertically, but L is mechanically constrained to remain in the horizontal plane. Therefore the rotation about the axis of τ is 0°. Therefore according to [itex]W = τ θ[/itex] the work done by the torque that makes the gyroscope precess is 0. 



#24
Jan713, 06:47 AM

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P: 244

I have now learned that precession will slowly turn the gyroscope in the same direction as the gyroscope is spinning. That precession will occour if a force, like gravity, is trying to overturn the gyroscope. Will it be possible to manually force the "precession" the opposite way if the gyro is still spinning the same way as before? If so, what happens with the speed of the gyro? Vidar 



#25
Jan713, 06:52 AM

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#27
Jan713, 09:47 AM

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Excellent! You are welcome.




#28
Jan813, 06:15 AM

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P: 244

Sorry  not finished yet
I would think that the flywheel mass that constantly changes direction, and thus experiences a form of "pseudo" acceleration or Gforces, would require a certain amount of energy in order to do this. Such as the "Coriolis" effect (Might be incorrectly expressed) of a centrifugal pump. Although the liquid can be returned to the pump input (a loop where the liquid repeats the same cycle), the acceleration of the fluid tangentially to the rotation as it flows away from the center of the pump will still try to prevent rotation. Where does the energy in such a system go? Will the liquid heat up? Vidar 



#29
Jan813, 07:16 AM

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#30
Jan813, 09:35 AM

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P: 244

OK, thanks. I just visualized the experiment where I place a red dot on the flywheels circumference. I rotate the flywheel 1 rps, and the flywheel have a circumference of 1 meter. The red dot travels now at 1m/s. If I turn the flywheel perpendicular to its rotation 1 complete turn per second, the red dot will cover a longer distance per revolution of the flywheel, and increase velocity by how much? Do you have an equation for this?
Vidar 



#31
Jan813, 10:49 AM

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I don't have that equation, although it shouldn't be too hard to derive.




#32
Jan1013, 04:11 PM

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P: 244

I have drawn an illustration in Google ScetchUp  hope you understand it.
It is a fast spinning flywheel (red) on a shaft (Blue). Two green guides prevents the shaft and the flywheel to move sideways. Gravity is pulling on the heavy flywheel. Question: As the spinning flywheel starts falling from the top (Not illustrated). Will the velovity of it be greatest at point A, B or C? What velocity can we expect at point A, B and C? Will the shaft with its spinning flywheel behave as longer pendulum (Kind of a pendulum in slow motion)? Vidar 



#33
Jan1113, 08:18 AM

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Anyone? Vidar 



#34
Jan1113, 10:51 AM

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That is a really annoying system to analyze. The weight will cause a torque about a horizontal axis which will try to get the gyroscope to precess horizontally. It will then run into the green guide which will exert a force to prevent its horizontal precession. This force will also generate a torque, this time about the vertical axis. The torque about the vertical axis will cause the gyroscope to precess either up or down until it reaches the top or the bottom. At that point gravity will no longer be exerting a torque and it will just stay there. It will not act as a pendulum.




#35
Jan1113, 01:31 PM

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P: 244

What is the reason why the weight will move upwards? One would think at first glance that the vertical torque is solely caused by the weight and gravity. Wether the precess wants to be clockwise or counterclockwise perpendicular to the guides wouldn't matter as there is no physical precess present due to the guides, right? If horizontal precess really is an important factor of which vertical direction the weight will move in this system, I will accept that  but have trouble in understanding why. In my mind, the spinning itself will cause increased "inertia" that is parallell with the force which pulls on it. However, I might not use the word inertia, but I couldn't find a better word. As this system will not act as a pendulum but stop at the bottom or the top, the weight will slowly move down or up, and rest there so the weight is spinning perpendicular to the force of gravity. I think: In this particular system the "inertia" would appear to be an artificial friction (As it would look like if one watched it  A pendulum in syrup), but it would not cause heat as the weight moves up or down in the guides. So instead of generating heat, the spinning weight must slow down. Energy must be conserved. If the force that pulls on the weight is allways perpendicular to the motioin of it (As if the gravity turns around the system in the direction of the weight), the weight will finally stop spinning. That applied force could likely be my finger trying to move the spinning weight up and down inside the guides  regardless if the guides is aligned vertical or horizontal. I tested something similar with a toy car that you push along the floor, and hear that iron flywheel spins up to high speed (Except I was using a powerful drill and almost destroied the gears inside). If I then turn that car left and right back and forth very fast perpendicular to the flywheel, that flywheel stops much earlier than if I don't. The needle bearings does not provide much friction anyways, so in case of increased friction I don't think this is the main reason why the flywheel stops faster. So, then I am back to the initial question in this thread. Analyzed the above system, I now put a gear to the weight so the weight is spinning because I push it along the guides. Whould't that mean that I try to accelerate the RPM of the weight at the same time as the shift of the wheel force to stop it's spin? While doing this, the force from my finger is moving a given distance. This will appearently end up with an energy consume from my side that is not going anywhere  not heat, not increased kinetic energy ??? Vidar 



#36
Jan1113, 02:57 PM

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The weight will cause a torque to the right so the gyro will want to precess to the right. Instead it will run into the guide which will prevent any precession to the right. The force that the guide exerts will in turn make a torque vertically down. Since the guides allow motion down the gyroscope will precess downwards. Once it reaches the bottom there will be no more torque due to gravity and therefore no more force from the guide and therefore no more torque from the guide and it will stop precessing. Why don't you try the analysis if the gyro is spinning clockwise (angular momentum directly away), and see if it precesses up or down. I don't actually know. 


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