0

When winding a bike wheel up in an elastic double string in the ceiling, and then let the wheel spin vertically, it unwinds more slowly than if it was not spinning. I tried it. But if a spinning disk is placed in a solid construction like this (photo attached) , and can only rotate horizontally as the blue plump falls, will the plumb likewise fall more slowly than if the gyroscope was not spinning? If no, why is the gyroscope not working the same way as with the string in the ceiling? I tried to simulate the situation in the photo with a moving front wheel of a bike, by could not detect a slower movement of the bike wheel, spinning versus not spinning. If the spinning gyroscope does slow down the falling plumb, how do I mathematically connect the speed of the wheel with the speed of the plumb? Please see my previous question.

enter image description here

Qmechanic
  • 201,751
Space Thoughts
  • 21

1 Answers1

2

In the case that you describe, calling it 'a solid construction', there will be no difference between the case of the gyro wheel spinning or the gyro wheel not spinning.

In order to discuss the case I need names for the three possible axes of rotation.

The image shows a gimbal mounted setup.

I define three axes:

  • Roll axis - the gyroscope wheel spins around the roll axis.
  • Pitch axis - motion of the red frame. As you can see, the gimbal mounting ensures the pitch axis is perpendicular to the roll axis.
  • Swivel axis - motion of the yellow frame.

I'm assuming that in the setup that you are describing the gyro wheel is prevented from pitching.

I'm assuming that because (obviously) the gyro wheel must be free to spin, and in order for the blue weight to have any effect the gyro wheel mounting must be free to swivel. Hence the description 'solid construction' must be saying that pitching motion is prevented.


The point is: in order for the gyroscopic effect to occur pitching motion must be allowed.

If the spin rate is very high a small amount of pitching motion is sufficient to oppose the pull of the blue weight. (The pitching motion arises at the start of swiveling motion. For a discusson of the mechanics see my 2012 answer about gyroscopic precession )


For further corroboration: I recommend you look up the way that stabilization with gyro wheels is implemented in luxury yacht gyro stabilization. The spin rate is very high, and the system has very strong actuators that actively change pitch angle in order to achieve the required effect.

If the suspension of the gyro wheels would simply be bolted onto the hull then the system would be just as ineffective as the setup in the image you uploaded.

If the setup in your image would have actuators that can change the pitch angle of the gyro wheel then a sufficiently fast spinning gyro wheel can lift the blue weight, by way of active change of the pitch angle.

Cleonis
  • 20,795
  • Hi Cleonis. Thank you for diving into my question with such a clear answer. Yes, you figured out what I meant. Basically I’m just very curious about the distribution of the total energy available in the system, and I wrote a question today based on your answer, that is way too long to post as a comment. What do people usually do when posting long comments in a thread? – Space Thoughts Dec 13 '21 at 15:29
  • @SpaceThoughts So, stackexchange is specifically designed for a question/answer format. I assume that design was developed because in a threaded forum the discussion tends to go off to various tangents. Here on stackexchange: if you have a follow-up question what you can do is write a new question, based on existing material. The idea is to try and write a standalone question, but for context you can link to an earlier question. – Cleonis Dec 13 '21 at 21:56