Interesting fact about a wheel.

[GSVR]

It's like a train wreck. Morbid fascination, if you will. I'm waiting for the Flat Earth Society to arrive and erect a stall.

I thought they already had when you showed up!

[Mikkel]

Don't worry - Hitcher's just here to check that we don't fuck up our spelling and grammar too much.
Dunno if he's on the ball as far as mechnics and vectors goes - but hey, he might be checking in on that as well.

Besides, he's at least in the top-5 as far as constructive input in this thread goes.

It's true, a Kiwi drag racing team back in the day had problems with the front tyres on their rail deflating with each run, they found out the valve spring pressure was being overcome by the centrifugal forces.

Simply putting on valve caps fixed the problem.'

Awesome. Cool to hear that it can actually happen.

Good thing that they have moved on to maglev trains - imagine what could happen on the TGV.

(And yes, that's a joke - sarcasm if you'd like...)

[Bonez]

My wheels went round and round today. They also went sideways, up, down and then they stopped. Wheels are very usefull things.

[avgas]

Good thing that they have moved on to maglev trains

Tell that to the account in Shanghai. Only a few billion US over the proposed budget.....and it never got finished due the fact that the EMF was enough to stop it being build closer than 100m from any buildings.
Shanghai is not known for big back yards either.
It did make me wonder - at what speed and weight do you consider the maglev a threat to derailment though (back to you G-force idea)

[Mikkel]

Tell that to the account in Shanghai. Only a few billion US over the proposed budget.....and it never got finished due the fact that the EMF was enough to stop it being build closer than 100m from any buildings.
Shanghai is not known for big back yards either.

Funny that, I actually have friends who recently went on that maglev train.

And it has cut down the travel time from the Shanghai centre to the airport significantly.

Magnetic fields can be shielded quite well. Besides - if you want to make a maglev train efficient you'd aim to make a strongly curved and very dense magnetic field which wouldn't have much of an outreach effect.

It did make me wonder - at what speed and weight do you consider the maglev a threat to derailment though (back to you G-force idea)

Huh?

[avgas]

And it has cut down the travel time from the Shanghai centre to the airport significantly.

Errr people square/garden would be where i put city centre.....and its about 3/4 hour drive (or Subway) from there. Mind due you have to keep into comparison that Shanghai is like 2-3 hours wide (driving/subway) and is infact broken up between Pudong and Pushi (spelt incorrectly so it sounds right) and a few other less minor cities. Anything they can do to improve the infrastructure there has to be good. But unfortunately most Shanghainese never use the Maglev.
Still the new Siemens subway set works good for most people.
And there still is the People's Busses.
Both of which branch out from that old race track they call the Peoples Park

[Hitcher]

Still the new Siemens subway set works good for most people.

One hopes that's not a euphemism for uterus?

And one also suspects that Captain Pugwash would be interested in Siemens trains...

[GSVR]

If the wheel exploded in an instant into lots of little pieces all the same size what directions and speeds would the pieces initially head in?

Lets say the red dots are 1 dollar coins attached at 45 degree intervals around a 0.6 metre PCD. The wheel is stationary and spun up to 27.78 metres/second (100 kph 884 rpm). As one of the red dots gets to exactly the bottom they are all released.

Because the wheel is stationary they all fly off at a tangent to the radius they are travelling around. After they have travelled 150 mm or about 0.0050 seconds a high speed photo is taken. The blue spots show where they will be. They will also be all travelling at near enough to 27.78 metres/sec. Because the wheel is sitting stationary apart from the rotation theres no other vectors to add.

To image the purple dots you have to be travelling alongside the wheel so that it appears to be stationary but it actually isnt as its rolling down the roadway at 100kph.
Again at the instant a red dot gets to the bottom all the red dots are released and after 0.0005 seconds a high speed photo is taken. The purple dots show where they would appear on the photo. These positions are the resultant vectors after adding the 27.78 metres/sec direction of travel vector to the angular vector of the tangent they release at.

[GSVR]

You're point of view is from a stationary position on the ground which is wrong, at least if you are considering the effect it has on the bike. Imagine the bike to be floating in mid air and the wheels are spinning at an rpm equal to 100kph, it is easy to see that both the top and bottom of the wheel carry equal momentum as relates to the bike.

If you get hit by the wheel of a bike then yes the top of the wheel would be carrying more momentum than the bottom, but i fail to see how that would be relevant as there would be bigger things to worry about.

Quote:
"In non-moving system wheel is seen as rotating around its bottom ( instant axis of rotation constantly moving forward with the wheel)."

The relevance is that it actually is carrying more momentum at the top when the bike is in motion so the top requires more force to alter its path.

Another way would be to sit a bike on a rolling road then the only parts that carry forward momentum are the chain. some engine components and the wheels. Of course they also carry the same amount of backawards momentum as well as up and downwards.

[Sanx]

Any ideas how much the radius of the tyre would increase at 100kph due to the gforce pulling it out?

Check out the rear tires on these guys. The radius is increasing like 40 cm when the tires start to rotate.
http://www.youtube.com/watch?v=Ls_ob...eature=related

To answer a much earlier question, the increase in radius on a bike tyre is measurable. At speeds of us to about 270, the rear 190/60 Dunlop I had on the Blade increased by about 1cm in radius. Enough to wear a hole through the rear hugger, anyway.

[Badjelly]

The relevance is that it actually is carrying more momentum at the top when the bike is in motion so the top requires more force to alter its path.

You think you can sneak that one in again without anyone noticing?

I'll paraphrase what I said about this earlier:

A body of mass m subject to a force F will undergo an acceleration of a = F/m, irrespective of how fast it's already going.

If a body is moving in a straight line at speed s and you then subject it to a sideways force F, then the rate at which the direction of motion changes will be ... well I can't be bothered doing the maths, but it will become smaller as s become larger.

The thing is, when you say that a body "requires more force to alter its path" as its speed increases, you're correct if you're making a statement about the rate of change of the direction of motion, but you're wrong if you're making a statement about the rate of change of velocity (AKA acceleration).

[GSVR]

I'll make it as simple as I possibly can.

1/ A mass is 10 grams is travelling at 100 meters per second and a force of 1 newton is applied at 90 degrees to the direction of travel.

2/ A mass of 10 grams is travelling at 200 meters per second and a force of 1 newton is applied at 90 degrees to the direction of travel.

After one second the the mass in the second example (2/) has travelled twice as far forward but the same amount 90 degrees to the direction of travel sideways as the first example (1/).

So to get it to the to move the same amount sideways in the same distance four times as much sideways force would have to be used. ie 4 newtons.

Now apply this logic to the 1 dollar coins in my last wheel example.

[Badjelly]

I'll make it as simple as I possibly can.

A mass is 10 newtons is travelling at 100 meters per second and a force of 1 newton is applied at 90 degrees to the direction of travel.

A mass of 10 newtons is travelling at 200 meters per second and a force of 1 newton is applied at 90 degess to the direction of travel.

After one second the the mass in the second example has travelled twice as far forward but the same amount 90 degrees to the direction of travel sideways.

So to get it to the to move the same amount sideways in the same distance twice as much sideways force would have to be used. ie 2 newtons.

There are a couple of things wrong with this: the units of mass are kilogrammes; and you'd actually need 4 times as much force to move the the second body the same distance sideways in the same distance of forward travel (because you have half the time to do it and s = (1/2)*a*t^2, well let's not go into that).

But, basically, yes. A faster-moving body requires more force to deflect it the same distance sideways in the same distance of forward travel.

[GSVR]

There are a couple of things wrong with this: the units of mass are kilogrammes; and you'd actually need 4 times as much force to move the the second body the same distance sideways in the same distance of forward travel (because you have half the time to do it and s = (1/2)*a*t^2, well let's not go into that).

But, basically, yes. A faster-moving body requires more force to deflect it the same distance sideways in the same distance of forward travel.

Kilograms are weight due to acceleration due to gravity
Mass is always newtons

Thanks for pointing out the error so example instead of 2 newtons I should have said 4 yes I get that now and have corrected it.

[Badjelly]

Kilograms are weight due to acceleration due to gravity
Mass is always newtons

Other way round, basically. The kilogram is a unit of mass.

http://en.wikipedia.org/wiki/Kilogram

The newton is a unit of force

http://en.wikipedia.org/wiki/Newton

One newton is the amount of force that is required to accelerate one kilogram of mass at a rate of one meter per second squared.

To confuse things, we usually estimate the mass of objects by weighing them, ie by measuring the force exerted on them by gravity. But the kilogram is definitely a unit of mass, so Dani Pedrosa would still have a mass of 51 kg if he were on the moon, even though his weight would be 1/6 that.