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

[Muhammad Uthman]

Why does fly wheel return in opposite motion after it comes to rest due to friction?

 

[Bystander]

Wind-up in the power train.

 

[CWatters]

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?

 

[Muhammad Uthman]

Rim? Hub? Spokes?

 

[Bystander]

I was thinking more in accumulated shaft lengths, pedestals, frames, linkages.

 

[CWatters]

Rim? Hub? Spokes?

My flywheel looks like a bicycle wheel with disc brake. What does yours look like?

 

[CWatters]

I was thinking more in accumulated shaft lengths, pedestals, frames, linkages.

Understood.

 

[Muhammad Uthman]

http://www.naugralabequipments.com/images/product/14692275775-250x250.jpg

 

[Muhammad Uthman]

The one in my Physics lab looks like this one.

 

[CWatters]

Can you describe what happens? For example is the string and weight still attached when it stops and goes backwards?

 

[Muhammad Uthman]

String and weight falls and it continues to rotate until comes to rest and rotates in opposite direction.

 

[jerromyjon]

What happens when you run out of string? I'm guessing the flywheel continues spinning and the string remains attached?

 

[Drakkith]

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?

 

[Muhammad Uthman]

Nope!

 

[Muhammad Uthman]

It happens the same if there is no string and we just give is a slight push by hand.

 

[jerromyjon]

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.

 

[NascentOxygen]

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?

 

[jerromyjon]

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.

 

[DaveC426913]

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.

 

[NascentOxygen]

I was picturing the slot in the shaft for the string end would always like to end up uppermost, if all else were ideal.

 

[Muhammad Uthman]

Every flywheel of this type does so.

 

[NascentOxygen]

Every flywheel of this type does so.

What type of flywheel do you mean?

 

[jerromyjon]

Almost anything that spins does it, more so with greater resistance.

 

[Muhammad Uthman]

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.

 

[Muhammad Uthman]

Almost anything that spins does it, more so with greater resistance.

Every spin returns?

 

[RonL]

Today I learned about "chat-bots", I'm getting the opinion this is not a serious question.

 

[dean barry]

at the bottom of the weights journey the string is wound back up in the opposite direction

 

[RonL]

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.

 

[jerromyjon]

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.

 

[jerromyjon]

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.

 

[CWatters]

I find it difficult to believe that a correctly designed heavy flywheel bearing would have enough friction recoil to make it rotate back much.

Edit: Can we see a video?

 

[sophiecentaur]

You could do some experiments, putting the wheel at various angles and letting it go to see where it goes.
Also, no one has suggested the possibility that this is an optical illusion. It could that there is no real reverse motion at all and that your brain is misinterpreting what you are seeing. There are many websites that show such illusions of motion. You can have an enjoyable Google session, finding them and seeing the effects.

This is a direct parallel with linear motion. Apart from a 'bounce' due to resilience in the system, you would hardly expect a mass that is brought to a halt, to move backwards after it comes to rest.

 

[jerromyjon]

I was going to make a video of my big old heavy door with really old hinges but as it tries to come to a stop it bounces back and forth a few times like a diminishing sine wave.

 

[jerromyjon]

I remember in younger days trying to "check" the balance factor of a bicycle wheel which did the same thing, I was able to make it not happen by loosening the bearings a bit.

 

[CWatters]

I've seen it with a door and a bike wheel but not a purpose designed flywheel.

 

[sophiecentaur]

It's just a matter of 'to bounce or not to bounce', surely. The general implication of the OP is wrong.

 

[Muti]

every rotating equipment need two things for smooth operation: balancing (simply mean, its mass must be homogeneous and alignment (simply mean, the two end which keep the fly wheel in proper place must be in a line) or else as DaveC told there would be wibbly-wobble (Vibrations). I think this set up is about function of fly wheel. Initially the work is done by string and weight due to gravity force, but when the string reach its end no further work can be done but fly wheel has stored energy due to its inertia... Ideally flywheel will give its energy in the form of torque in the same direction, but perhaps some one else give reason how it change its direction (may be due to third law of motion...)[PLAIN]https://www.physicsforums.com/members/davec426913.15808/[/PLAIN]