Einstein was right again

[drewski]

http://science.nasa.gov/science-news/science-at-nasa/2011/04may_epic/

Experiments prove the existence of curved space time around the earth.
Interesting stuff.

[54ny77]

after consuming a few donuts, the geodetic precession of 6.600 plus or minus 0.017 arcseconds and a frame dragging effect of 0.039 plus or minus 0.007 arcseconds is observed on the belly, thus proving the theorem.

http://www.clevescene.com/images/blogimages/2011/03/30/1301539547-fat-guy.jpg

[JStonebarger]

Yeah, well, lucky guess.

[flydhest]

Yeah, but Einstein is the guy who said that life is like bicycling, to keep your balance you must keep moving. Schmuck must never have learned to track stand.

[RPS]

Yeah, but Einstein is the guy who said that life is like bicycling, to keep your balance you must keep moving. Schmuck must never have learned to track stand.
For a smart guy, based on picture above, he didn't know much about proper fit either. :rolleyes:

[Mark McM]

Yeah, but Einstein is the guy who said that life is like bicycling, to keep your balance you must keep moving. Schmuck must never have learned to track stand.

In a track stand, the bicyclist also must continuously move to maintain balance. They just aren't continuously moving forward (i.e. they rock back and forth over one spot).

[gasman]

Einstein was the man.
Great link I knew about the experiment but hadn't heard the result.

[flydhest]

In a track stand, the bicyclist also must continuously move to maintain balance. They just aren't continuously moving forward (i.e. they rock back and forth over one spot).

Nope, no need to continue to rock back and forth. That is a practice for people who don't really have the hang of it.

[R2D2]

after consuming a few donuts, the geodetic precession of 6.600 plus or minus 0.017 arcseconds and a frame dragging effect of 0.039 plus or minus 0.007 arcseconds is observed on the belly, thus proving the theorem.

http://www.clevescene.com/images/blogimages/2011/03/30/1301539547-fat-guy.jpg

Hey Einstein put on some weight no?

[Mark McM]

Nope, no need to continue to rock back and forth. That is a practice for people who don't really have the hang of it.

I dare you to lock the front brake and try to stay in one spot for any length of time.

[goonster]

I dare you to lock the front brake and try to stay in one spot for any length of time.
+1

There is movement, even if the adjustments are very small. Even better: try trackstanding on a bike with no chain.

[flydhest]

Mark,
I was mostly joking, but to take the issue seriously, perhaps it is semantic, but I see a difference between keeping balance and regaining balance. The thread about the bike design without trail or gyroscopic moment highlights it for me. The rocking is to re-establish balance if/when it is lost. As for the brake, I have actually done that while screwing around. I think a question is what you mean by "any length of time." Given that we are discussing one of the great theoretical physicists, "any length of time" is open to interpretation.

As for the chain, I think of that as irrelevant. The quotation is about motion, not force. There (usually) needs to be some force put into the bike to track stand (although I am now likely going to experiment), but given that that force is usually being used to balance against a different force (usually gravity) no movement need be involved. As a result, the chain issue is a bit beside the point.

[RPS]

+1

There is movement, even if the adjustments are very small. Even better: try trackstanding on a bike with no chain.
In theory, do you think it may be possible for some very talented people to balance by continually applying steering input which would shift the center of gravity due to trail?

Even so, Einstein would still be right. It’s movement nonetheless; just not back and forth but side to side.

[RPS]

Mark,
I was mostly joking, but to take the issue seriously, perhaps it is semantic, but I see a difference between keeping balance and regaining balance. The thread about the bike design without trail or gyroscopic moment highlights it for me. The rocking is to re-establish balance if/when it is lost. As for the brake, I have actually done that while screwing around. I think a question is what you mean by "any length of time." Given that we are discussing one of the great theoretical physicists, "any length of time" is open to interpretation.

As for the chain, I think of that as irrelevant. The quotation is about motion, not force. There (usually) needs to be some force put into the bike to track stand (although I am now likely going to experiment), but given that that force is usually being used to balance against a different force (usually gravity) no movement need be involved. As a result, the chain issue is a bit beside the point.
I think the forces you refer to are used to shift the rider's center of gravity side to side as needed to keep it over the tires contact so the rider doesn't fall over in either direction. That's what balance means to me. Either way, movement is required -- forces will result in movement otherwise they don't do any good.

[MadRocketSci]

anyway...

a shout out to Dr. Hugh Dougherty, who, while he would never admit it, is "smarter than the average bear." (<- one of his favorite phrases) The man has made great contributions to our understanding of the universe by designing the control systems for the Hubble and GP-B, as well as being the program manager for them.

Why am I posting this here? I dunno....

http://www.scu.edu/engineering/me/adjunct/dougherty.cfm

[wooly]

http://www.clevescene.com/images/blogimages/2011/03/30/1301539547-fat-guy.jpg[/QUOTE]

Is that Petacchi?

[flydhest]

I think the forces you refer to are used to shift the rider's center of gravity side to side as needed to keep it over the tires contact so the rider doesn't fall over in either direction. That's what balance means to me. Either way, movement is required -- forces will result in movement otherwise they don't do any good.

Err, no. Put a 10 pound weight on a spring. Gravity is working with the weight to exert force downward. The spring is exerting force upward. When they settle, there will be no movement and yet forces. I don't think, however, that forces think in terms of whether they are doing good.

The forces I was refering to are putting pressure on the pedals in a case where the front wheel is turned (often, slightly uphill) and one equalizes that force from the pedals (which would cause the bike to go forward) with the force from the tire (caused by gravity if it is pointing slightly up hill). If the two forces are equalized, there shouldn't be movement.

Put two equal weights on a see-saw, they will not move. They will be balanced. Balance, to me, means forces being equalized.

I just got back from a quick walk at lunch today and talked to the man himself. He says there must be more interesting things to discuss:
http://www.nasonline.org/site/PageServer?pagename=ABOUT_building_einstein_memori al

(My office is a block away.)

[MadRocketSci]

track stand - a version of the inverted pendulum problem?

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

cg above pivot point - unstable. Thus, if you could manage to perfectly balance out all forces and moments such that sum F = 0 and sum Torque = 0 then you will maintain equilibrium. problem is that this does not happen in reality. disturbances abound, even if tiny. Thus, being unstable, means that stabilizing forces are needed. is motion necessary to apply these forces? I would say yes, in the real world.

you can build an inverted pendulum controller that looks like it is holding the rod upright perfectly. You might not be able to see the motion, but given high enough sample rates (assuming digital control) and quality sensors/actuators, the minute accelerations (and hence even smaller motions) are there. Same probably goes if you're really good at track standing.

What I find amusing in this discussion is the economist saying "it is this way in theory" and thus QED it must be possible in practice. No disrespect, just mentioning that it is fitting with my conception of the way the field is practiced.

I'm out....

[flydhest]

What I find amusing in this discussion is the economist saying "it is this way in theory" and thus QED it must be possible in practice. No disrespect, just mentioning that it is fitting with my conception of the way the field is practiced.

I'm out....

Not what I'm saying at all. I made one simple comment, that I still think is right, by the way, and then went into a different discussion about the theory later when RPS presented his view of what balance means. Seems reasonable to me, he gave his definition, I supplied mine. That effort is an important part of a discussion.


I don't track standing as an inverted pendulum.

Lean two playing cards against each other, there's theory and practice together.

Moreover, I would say that there are plenty of economists who are of the mindset "sure it works in practice, but does it work in theory" as there are "sure it works in theory, but does it work in practice"

[RPS]

Err, no. Put a 10 pound weight on a spring. Gravity is working with the weight to exert force downward. The spring is exerting force upward. When they settle, there will be no movement and yet forces. I don't think, however, that forces think in terms of whether they are doing good.

The forces I was refering to are putting pressure on the pedals in a case where the front wheel is turned (often, slightly uphill) and one equalizes that force from the pedals (which would cause the bike to go forward) with the force from the tire (caused by gravity if it is pointing slightly up hill). If the two forces are equalized, there shouldn't be movement.

Put two equal weights on a see-saw, they will not move. They will be balanced. Balance, to me, means forces being equalized.

I just got back from a quick walk at lunch today and talked to the man himself. He says there must be more interesting things to discuss:
http://www.nasonline.org/site/PageServer?pagename=ABOUT_building_einstein_memori al

(My office is a block away.)
I don’t think I need a physics lesson; but you need to read my entire post and not only the part you select to disagree with as a stand-alone item. That’s the proverbial taking things out of context. ;)

I didn’t state that forces can’t balance or cancel each other without causing movement, did I? But I did say that when applied in such a way that it doesn’t cause movement then they are useless towards the task at hand.

I know better than most than when two equal forces are opposing they can cancel each other and nothing much may happen. But in that case, nothing useful will happen towards balancing a bike either. For instance, internal frame forces acting against each other may cancel out (many do when taken as a whole), but they essentially cause no relative movement between the “practically” rigid frame components. These internal frame forces therefore do absolutely nothing to help balance a bike. My point was that forces alone don’t do squat, they have to result in useful movement.

With all due respect, the example you give about the see-saw is not comparable to balancing a bike because a see saw is inherently stable by comparison. When two equal (or near equal) weights are applied at opposite ends they may cancel, and there is enough friction in the middle to keep the see saw from moving. It’s a very stable system in that sense compared to a bike.

A bike/rider’s combined mass is always above the pavement, where the tires make contact with the ground. Regardless of how well it may be balanced initially, it won’t stay there very long if left alone because it’s inherently unstable. Left alone, there is nothing to counter it falling once it starts to go in either direction. That’s were the rider has to apply useful forces to shift mass from side to side relative to tire contact to keep things balanced.

It’s not much different than a tight rope walker who is constantly moving to stay balanced. If he didn’t make corrective movements constantly it’s only a matter of (very short) time before he goes down.

[RPS]

Moreover, I would say that there are plenty of economists who are of the mindset "sure it works in practice, but does it work in theory" as there are "sure it works in theory, but does it work in practice"
I've always thought that when the two don't agree, it's because the theory is not correct or applied correctly.

If theory is truly correct, why shouldn't it work all the time?

[goonster]

As for the chain, I think of that as irrelevant.
Agreed, but the cranks are our primary method of input while trackstanding.

I see a difference between keeping balance and regaining balance. The thread about the bike design without trail or gyroscopic moment highlights it for me. The rocking is to re-establish balance if/when it is lost.
Einstein used the bicycle to make an analogy about life. You (ok, jokingly) refute the analogy by citing an unstable system that is motionless for very brief periods before requiring corrective motion. If you are more right than Einstein, you'd be able to perfectly balance a bicycle on level ground with no wind and have it remain standing without corrective inputs.

I will concede though, in concurrence with your original comment, that it is highly unlikely that Einstein considered a trackstanding cyclist when making his quip.

In theory, do you think it may be possible for some very talented people to balance by continually applying steering input which would shift the center of gravity due to trail?
Yes, given an absence of large external inputs, e.g. gusts of wind, etc.

[goonster]

If theory is truly correct, why shouldn't it work all the time?
1. Because the theory can be true for large populations and still tell us nothing about a very small sample size.

2. Because the required conditions cannot always be created for an experiment, e.g. there are no perfectly elastic collisions, we can't accelerate mass to the speed of light, etc.

[MadRocketSci]

Lean two playing cards against each other, there's theory and practice together.


That is a stable system. Small disturbances will not cause the system to collapse. The disturbances result in restoring mechanisms which prevent this.

a mass over a pivot point (since the brakes are locked) is unstable. small disturbances uncompensated with restoring forces/motion will cause the system to collapse.

[Louis]

So now that we've confirmed what gravity is, who's going to explain to me what time is?

[Mr. Squirrel]

mr. einstein was a smart. i do not like his wheels, they are not flashy enough nor did he use a quick release. when it involves nuts, i am very smart.

http://www.viddler.com/thechive/videos/109/

i do not think mr. einstein can match me.

mr. squirrel

[Dekonick]

For a smart guy, based on picture above, he didn't know much about proper fit either. :rolleyes:

Perhaps... or perhaps not....

In a hundred years we may find he was right all along... just ask how many Phd's out there told him he was wrong before... only to find out later he actually was right :)

Somehow I think you are probably right on this account... but that is one of the few where Einstein is involved.

He was even smarter than we thought he was...

[Dekonick]

track stand - a version of the inverted pendulum problem?

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

cg above pivot point - unstable. Thus, if you could manage to perfectly balance out all forces and moments such that sum F = 0 and sum Torque = 0 then you will maintain equilibrium. problem is that this does not happen in reality. disturbances abound, even if tiny. Thus, being unstable, means that stabilizing forces are needed. is motion necessary to apply these forces? I would say yes, in the real world.

you can build an inverted pendulum controller that looks like it is holding the rod upright perfectly. You might not be able to see the motion, but given high enough sample rates (assuming digital control) and quality sensors/actuators, the minute accelerations (and hence even smaller motions) are there. Same probably goes if you're really good at track standing.

What I find amusing in this discussion is the economist saying "it is this way in theory" and thus QED it must be possible in practice. No disrespect, just mentioning that it is fitting with my conception of the way the field is practiced.

I'm out....

God I love this forum! What a weird bunch we are... after all we wear lycra...

[Dekonick]

I don’t think I need a physics lesson; but you need to read my entire post and not only the part you select to disagree with as a stand-alone item. That’s the proverbial taking things out of context. ;)

I didn’t state that forces can’t balance or cancel each other without causing movement, did I? But I did say that when applied in such a way that it doesn’t cause movement then they are useless towards the task at hand.

I know better than most than when two equal forces are opposing they can cancel each other and nothing much may happen. But in that case, nothing useful will happen towards balancing a bike either. For instance, internal frame forces acting against each other may cancel out (many do when taken as a whole), but they essentially cause no relative movement between the “practically” rigid frame components. These internal frame forces therefore do absolutely nothing to help balance a bike. My point was that forces alone don’t do squat, they have to result in useful movement.

With all due respect, the example you give about the see-saw is not comparable to balancing a bike because a see saw is inherently stable by comparison. When two equal (or near equal) weights are applied at opposite ends they may cancel, and there is enough friction in the middle to keep the see saw from moving. It’s a very stable system in that sense compared to a bike.

A bike/rider’s combined mass is always above the pavement, where the tires make contact with the ground. Regardless of how well it may be balanced initially, it won’t stay there very long if left alone because it’s inherently unstable. Left alone, there is nothing to counter it falling once it starts to go in either direction. That’s were the rider has to apply useful forces to shift mass from side to side relative to tire contact to keep things balanced.

It’s not much different than a tight rope walker who is constantly moving to stay balanced. If he didn’t make corrective movements constantly it’s only a matter of (very short) time before he goes down.

Oh boy - y'all are getting me excited! Don't make me do it... Don't... NOOOOOooo


No matter how hard you try, you can NEVER achieve a static situation. There will always be quantum effects... small as they are... and thus true stability is impossible... and let's not even start talking about entropy...

:)

I love this stuff... wack as it is...

[Dekonick]

That is a stable system. Small disturbances will not cause the system to collapse. The disturbances result in restoring mechanisms which prevent this.

a mass over a pivot point (since the brakes are locked) is unstable. small disturbances uncompensated with restoring forces/motion will cause the system to collapse.


Eventually they will fall. I guarantee it. You will always have entropy to deal with...

HOWEVER - you are correct in the short term. A bridge is stable. Give it 1000 years, or more... and eventually entropy will have it's way.

To think one day we will be nothing more than scattered bits in a sea of nothingness... beautiful in an odd way.

[Dekonick]

So now that we've confirmed what gravity is, who's going to explain to me what time is?


Ahhh - but we aren't really sure we know gravity... there is a *possibility* that it is a much stronger force than we thought... and it is just 'leaking' into the 3-brane we live in...

I don't know... these freaking strings keep me tied up! :crap: :bike: :rolleyes: :hello:

[MadRocketSci]

God I love this forum! What a weird bunch we are... after all we wear lycra...

here's some physics porn (http://www.youtube.com/watch?v=MWJHcI7UcuE) for ya bro....

[Louis]

here's some physics porn (http://www.youtube.com/watch?v=MWJHcI7UcuE) for ya bro....

Cool.

Watching anything that has closed loop feedback is pretty neat.

[RPS]

here's some physics porn (http://www.youtube.com/watch?v=MWJHcI7UcuE) for ya bro....
Finally proof that it takes physicists and computers to balance an inverted pendulum as efficiently as the chimps in the circus have been doing for decades. That’s real progress. ;)


P.S. – On a serious note, even though the man is doing much of the balancing work, it must be quite a challenge to do this trick when both parties can independently affect the outcome. Coordination between the two must be extraordinary. Maybe it's analogous to doing a track stand on a tandem.

[fiamme red]

This is what a bike looks like after it has been sucked through a space-time vortex. The frame is slightly warped, as you can see.

http://bike.woodvillage.co.uk/bike/img/derosa_TANGO.jpg

[JStonebarger]

... There will always be quantum effects... small as they are...

Yeah, well, Einstein was right about some things, anyway.

[Dekonick]

here's some physics porn (http://www.youtube.com/watch?v=MWJHcI7UcuE) for ya bro....

Heh - cool.