Interesting fact about a wheel.

[Badjelly]

My point is - if you want to consider a wheel from a mechanical perspective it makes no sense to treat the upper and the lower part of the wheel as two seperate entities. It's ONE wheel and should be treated as such.

Agreed. I only said you can calculate the momentum vectors of the top and bottom halves separately. I didn't say you that doing so was a useful step towards understanding the mechanics. The mechanics of a spinning wheel are best understood in terms of the concepts you have been suggesting: mass, centre of mass, linear momentum, moment of inertia, angular momentum, etc.

If GSVR is wrong about something, let's at least be clear about where that is. That way we can all learn.

[GSVR]

The direction the wheel turns does not impact on it's stability - only the magnitude of the angular momentum.

I think I'm making real progress. What impact does it have on the angular momentum?

[Badjelly]

I'll turn this around a bit and say which direction would the wheel be the most stable. Turning like it would going down the road or in reverse. Or maybe it doesnt matter. ( By saying this I'm going against what I believe to be true)

My answer: it doesn't matter. (Bearing in mind that I'm not 100% sure what you mean by "stable".)

Like I said 1 or 2 posts ago, put walls around your train carriage so you can't see the scenery going past and there's no way you can tell from the behaviour of the spinning wheel (or any other mechanical object inside the carriage) which way the train is moving.

Which direction of rotation do you think would make the wheel more stable and why?

[Badjelly]

The direction the wheel turns does not impact on it's stability - only the magnitude of the angular momentum.

A slip of the keyboard? The direction the wheel turns does not impact on the magnitude of the angular momentum, only on the direction of the angular momentum vector.

[Mikkel]

I think I'm making real progress. What impact does it have on the angular momentum?

A slip of the keyboard? The direction the wheel turns does not impact on the magnitude of the angular momentum, only on the direction of the angular momentum vector.

Yes, of course. Silly me - the magnitude is affected by the rate of rotation, not the direction.

And regarding the direction - change the direction of rotation and you "flip" the vector representing the angular momentum.

[GSVR]

My answer: it doesn't matter. (Bearing in mind that I'm not 100% sure what you mean by "stable".)

Like I said 1 or 2 posts ago, put walls around your train carriage so you can't see the scenery going past and there's no way you can tell from the behaviour of the spinning wheel (or any other mechanical object inside the carriage) which way the train is moving.

Which direction of rotation do you think would make the wheel more stable and why?

I would have thought that if the wheel was rotating in the same direction as the train is going. ie same way as the train wheels the top would be more resistant to direction changes than the bottom half as its got more momentum.

The effect would be the same no matter which way the wheel rotated but it would be different to if it wasn't spinning at all.

[Mikkel]

I would have thought that if the wheel was rotating in the same direction as the train is going. ie same way as the train wheels the top would be more resistant to direction changes than the bottom half as its got more momentum.

Mate, seriously - stop asking more questions and read the Wikipedia page on Frame of Reference it should help to clear out that misconception that the fact the train is moving has any impact at all upon how the wheel behaves.

The effect would be the same no matter which way the wheel rotated but it would be different to if it wasn't spinning at all.

Which effect are you thinking about here.

The resistance to direction changes are derived from the angular momentum of the wheel - not that it is moving one way or the other, but that it's rotating. This is a gyroscopic effect. All gyroscopic forces are proportional to the angular frequency - as such there are no gyroscopic forces if the wheel is not turning.

[GSVR]

The top half has its spinning momentum(positive) plus the trains forward velocity. The bottom half has the spinning momentum(negative) plus the trains forward velocity.

For a wheel spinning same way as the train wheels.

[Mikkel]

The top half has its spinning momentum(positive) plus the trains forward velocity. The bottom half has the spinning momentum(negative) plus the trains forward velocity.

For a wheel spinning same way as the train wheels.

Admit it - you're just trolling. Nothing else!

[GSVR]

Admit it - you're just trolling. Nothing else!

Mikkel I know your a smart guy. But I really thought you might be able to explain yourself without refering me to youtube or Wickypedia who require an expert to fix their page.

"This article or section is in need of attention from an expert on the subject." Well they aren't getting me lol.

[Badjelly]

The top half has its spinning momentum(positive) plus the trains forward velocity. The bottom half has the spinning momentum(negative) plus the trains forward velocity.

For a wheel spinning same way as the train wheels.

I'm (finally) with Mikkel on this. To understand the mechanics of rotating objects you can work it out for yourself or you can try to understand what other people have found out in the last 300 years. Your line of reasoning is not going anywhere useful as far as I can see. The fact that the equations of motion are the same in any inertial frame of reference (ie one moving at a constant speed, eg our train carriage) is pretty basic and if you have reasoning that leads to a different conclusion, then your reasoning is probably wrong. (Sometimes it can be useful to work out why. Sometimes not.) Take it from someone who has made plenty of mistakes himself.

[Badjelly]

Mikkel I know your a smart guy. But I really thought you might be able to explain yourself without refering me to youtube or Wikipedia who require an expert to fix their page.

Wikipedia is a marvellous resource, not perfect of course, and if something is explained there, why reinvent the wheel. (Yes, that's a pun.)

[Badjelly]

Admit it - you're just trolling. Nothing else!

Most trolls don't put in quite as much work as GSVR has. He may be a bit stubborn, but I don't think you can call him a troll.

[GSVR]

Wikipedia is a marvellous resource, not perfect of course, and if something is explained there, why reinvent the wheel. (Yes, that's a pun.)

When I was at intermediate school many years ago a teacher was explaining electricity to the class. His theory was that cables had many strands to carry more power as electricity only moved over the surface of the wire.

Go figure

I'm actually not concerned about any gyroscopic coupling here its something that doesn't come into this equation. All its about is measuring momentum in one direction.

Hey got to go thanks to Mikkel and Badjelly its be good reading your posts and made me think. The decoy thread seemed to work well too.

[Mikkel]

Mikkel I know your a smart guy. But I really thought you might be able to explain yourself without refering me to youtube or Wickypedia who require an expert to fix their page.

Being a smart guy I have no intentions of writing a book on a subject that is already well covered. I am sorry if you feel that youtube and wikipedia are not good enough to be used as demonstration tool and textbook reference respectively. However, my own mechanics book is in danish and scanning and posting stuff from that won't help you. I can't show you the demonstrations online since I haven't got a webcamera. I'm truly sorry if you feel I can't help you with the resources that are available.

If I was sitting next to you making sketches and explaining the maths would be easy. Seeing as I actually did teach classes of approximate 25 engineering students at my old university for two years while studying to supplement my scholarship I have a reasonable confidence in my ability to communicate this subject. What I may not be confident about is whether your background is sufficient to deal with the subject at the level I am prepared to teach.

On the other hand if you're too lazy or too impatient to peruse the resources I have provided you with - then I can only say that it's extremely arrogant wanting to understand without wanting to learn. And learning requires study.

"This article or section is in need of attention from an expert on the subject." Well they aren't getting me lol.

It's classical mechanics. It's well understood. If there was anything directly wrong in the page it would have been corrected a long time ago. Classical mechanics is not a subject which is under contention.