Flywheel -- Why does it reverse direction after spinning to a stop?

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Discussion Overview

The discussion centers around the behavior of a flywheel, specifically why it appears to reverse direction after coming to a stop due to friction. Participants explore various aspects of flywheel mechanics, including the effects of mass distribution, friction, and external forces, while considering both theoretical and practical implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that friction in the axle may cause the flywheel to rotate in the opposite direction after it stops.
  • Others propose that the distribution of mass in the flywheel, particularly if it is not symmetrical, could influence its behavior upon stopping.
  • A participant mentions the concept of "friction recoil" and speculates on how it might affect the flywheel's motion.
  • There are discussions about the role of the string and weight in the flywheel's operation, with some asserting that the string's presence does not affect the reversal of motion.
  • Some participants question whether the observed reversal could be an optical illusion rather than a physical phenomenon.
  • Several participants share personal experiences with similar behaviors in other rotating systems, such as doors and bicycle wheels, but express skepticism about the same occurring in a purpose-designed flywheel.
  • One participant emphasizes the importance of balancing and alignment for smooth operation of rotating equipment, suggesting that these factors could influence the flywheel's behavior.

Areas of Agreement / Disagreement

Participants express a range of views on the mechanics of the flywheel, with no consensus reached on the exact reasons for the observed reversal of motion. Some agree on the influence of friction and mass distribution, while others challenge these ideas or propose alternative explanations.

Contextual Notes

Participants note various assumptions and conditions that may affect the flywheel's behavior, such as the design of the flywheel, the presence of friction, and the symmetry of mass distribution. These factors remain unresolved in the discussion.

Who May Find This Useful

This discussion may be of interest to individuals studying mechanical systems, physics students exploring rotational dynamics, or hobbyists experimenting with flywheel designs.

Muhammad Uthman
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Why does fly wheel return in opposite motion after it comes to rest due to friction?
 
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Wind-up in the power train.
 
If most of the mass is in the rim and friction acts at the hub then I guess there might be stress in the spokes if it decelerates rapidly?
 
Rim? Hub? Spokes?
 
I was thinking more in accumulated shaft lengths, pedestals, frames, linkages.
 
Muhammad Uthman said:
Rim? Hub? Spokes?

My flywheel looks like a bicycle wheel with disc brake. What does yours look like?
 
Bystander said:
I was thinking more in accumulated shaft lengths, pedestals, frames, linkages.

Understood.
 
http://www.naugralabequipments.com/images/product/14692275775-250x250.jpg
 
The one in my Physics lab looks like this one.
 
  • #10
Can you describe what happens? For example is the string and weight still attached when it stops and goes backwards?
 
  • #11
String and weight falls and it continues to rotate until comes to rest and rotates in opposite direction.
 
  • #12
What happens when you run out of string? I'm guessing the flywheel continues spinning and the string remains attached?
 
  • #13
Muhammad Uthman said:
String and weight falls and it continues to rotate until comes to rest and rotates in opposite direction.

Is it winding the string and weight back up?
 
  • #14
Nope!
 
  • #15
It happens the same if there is no string and we just give is a slight push by hand.
 
  • #16
Friction recoil in the axle. Can't seem to find any links about it.
I would imagine if it was very hard to turn, not from the weight itself but from the axle not wanting to turn, like a bicycle wheel with stiff bearings, it would be "springy" if you tried to turn it. When you do apply enough force to turn the wheel that extra force remains counter to the direction of rotation. As the energy left in the momentum dwindles below the friction threshold, the remaining energy is released in counter-rotation. Similar to if you apply less force to the wheel than it takes to turn the axle and release.
 
  • #17
If it wasn't perfectly symmetrical it would want to turn until the heavy spot was downwards, and sometimes this will entail reversal of its rotation at the end, but not always. A handful of trials should discount this as the source.

So you have removed all of the string? Is it fixed to the shaft by a knot wedged into a slot, or how?
 
  • #18
There also has to be some room in between the axle and the bushing where the axle can "walk up" the inner circumference of the bushing.
 
  • #19
NascentOxygen said:
If it wasn't perfectly symmetrical it would want to turn until the heavy spot was downwards,
A flywheel with this trait would have - let's say ... undesirable side effects.[EDIT] ohhhh. This is a high school flywheel. I was imagining a 10kg flywheel rotating at 30,000 rpms, developing a slight ... wibbly-wobble.
 
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  • #20
I was picturing the slot in the shaft for the string end would always like to end up uppermost, if all else were ideal.
 
  • #21
Every flywheel of this type does so.
 
  • #22
Muhammad Uthman said:
Every flywheel of this type does so.
What type of flywheel do you mean?
 
  • #23
Almost anything that spins does it, more so with greater resistance.
 
  • #24
It happens always, so there is nothing like unequal distribution of mass.
And string has nothing to do with it.
String is just in this pic I found at Google Images.
 
  • #25
jerromyjon said:
Almost anything that spins does it, more so with greater resistance.
Every spin returns?
 
  • #26
Today I learned about "chat-bots", I'm getting the opinion this is not a serious question.:rolleyes:
 
  • #27
at the bottom of the weights journey the string is wound back up in the opposite direction
 
  • #28
Muhammad Uthman said:
Why does fly wheel return in opposite motion after it comes to rest due to friction?
Why does it reverse direction after spinning to a stop? Why does fly wheel return in opposite motion after it comes to rest due to friction?
With all the guesses being denied as correct solutions, I have never in my personnel life had a flywheel do what you seem to be suggesting.

Thanks for putting a picture in your profile, it's a help:) I am interested in the question.
 
  • #29
Swing a door partially closed or open it does the same thing. It springs back just a slight bit. Probably less if it had bearings... but its just a stiff hinge friction recoil.
 
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  • #30
dean barry said:
at the bottom of the weights journey the string is wound back up in the opposite direction
The image was an example, the string and weight have to be removed.
 

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