Roller Coaster Race

[Grimer]

This video is rather fun, if only because of the soundtrack and canned laughter.

http://www.youtube.com/watch?v=jlSv_IlXmBg

and the following comment is pertinent to the search for PM (though I suspect it was made by the video maker to point up the enigmatic nature of the demonstration).

"that is actualy kind of intersting, i was thinking they would reach the final point at the same time, because when you drop or throw a ball at the same height they both land at the same time.? the acceleration the one going down the hill would be partly canceled out by the one going up and they should both reach them at the same time..... at least that was my thoughts, i guess i was wrong"

Consider the following example of the same phenomena.



If we let a cart roll through the blue valley starting at A and finishing at B then it will arrive at B earlier than a similar cart rolling through the red valley. Not only is its speed greater but so is the distance travelled.

Surely we must be able to use this in some way to obtain perpetual motion.

Any suggestions?

[pequaide]

It is like two pendulums of different lengths

Momentum transfer is the means of making energy.

[nicbordeaux]

First of all, we need to see the two cars interchanged to make sure their performance is identical. No two cars are ever the same. In this vid, the yellow car always travels the top. Maybe it's the most "free-rolling" one, in which case the demo is even more valid. But if it is the car which when released on a track absolutely identical to a second track on which the green car would roll on, and the green one always get's there first, the demo is totally flawed.

Yo Peq, if you look at your drawing it's a bicycle rim cut in two with a slightly concave top welded or rivetted to it. Stick your carts on this, and see what happens ;)

Obviously, linear travel over time is going to dictate which way the assy tips if you leave it free to rock because the positions of each cart will be mass one side or the other of the middle.

That would be very similar to a device I'm working on. But not identical. Let us know how it goes, and if you start flinging 40 gramme bags of lead with the rim rocker track, lemme know will ya ?

[Grimer]

It is like two pendulums of different lengths ...

Full marks.

Not only is it "like" two pendulums, it IS two pendulums since the essence of pendulum action is the path of the bob, not whether it is held to its path by a tensile or compressive force.



http://www.physics.brown.edu/physics/de ... 3a1050.htm

How do the paths differ in terms of energy?

[Grimer]

First of all, we need to see the two cars interchanged to make sure their performance is identical. No two cars are ever the same. In this vid, the yellow car always travels the top. Maybe it's the most "free-rolling" one, in which case the demo is even more valid. But if it is the car which when released on a track absolutely identical to a second track on which the green car would roll on, and the green one always get's there first, the demo is totally flawed. ...

You seem to be having problems in believing the demo is genuine, Nic.
Maybe you are feeling the same cognitive dissonance of the person who commented on the video.

[nicbordeaux]

Wrong Frank, totally wrong. I have two builds, one with fluids, one a wheel, attempting to use that differential. Call it latency.

My point is that if there is no point in leaving open a window for critics when trying to make a point. Reversing the cars, changing tracks, would put a end to any possible dispute before it started. Still, I maintain the "carts" differ wildly in performance, only takes a slightly bent axle, and it would have been nice to see an averaged out performance. But maybe you had a underprivilged childhood and didn't have access to other peoples rubbish bins where you could salvage other kids' discarded and foul smelling rotting food covered toys to play with , and thus learn how those little plastic Noddy cars behave ?

Murilo : no kidding, slice a bike rim in two, assemble (rivet, weld...) the two halves side by side with a smal spacing so you have a track for a ball to ride. The top you want as two rods spaced so that a ball can travel too. It's fun. At a later stage when you get fed up with playing with the thing, add a pendulum like on a milokovovitch oscillator. The pivot point of course is the contact point between curved rim halves and ground.

[Grimer]

Seems to me he was just giving an interesting demo, not trying to convert doubters.

[murilo]

Wrong Frank, totally wrong. I have two builds, one with fluids, one a wheel, attempting to use that differential.........

Murilo : no kidding, slice a bike rim in two, assemble (rivet, weld...) the two halves side by side with a smal spacing so you have a track for a ball to ride. The top you want as two rods spaced so that a ball can travel too. It's fun. At a later stage when you get fed up with playing with the thing, add a pendulum like on a milokovovitch oscillator. The pivot point of course is the contact point between curved rim halves and ground.

Nic, hi...
I know I'm just a troll, but at this time I'm innocent, ok? I'm innocent!!! 8[
Best!
Milokovo... sorry, Muliro.

[Fletcher]

Frank .. this is essentially a "brachistochrone" problem.

http://curvebank.calstatela.edu/brach77/brach77.htm

It has been discussed on this board many times - try a search for a decent animation & explanation.

---------------------------------------

Surely we must be able to use this in some way to obtain perpetual motion.

Your example shows the start height & end heights the same although the steepness of the track varies - if you think about it a steeper track allows the mass to accelerate quickly due 'g' thus greater mean speed & earlier arrival time.

BUT ..

No Work was Done in physics terms because the start & finish height are the same, so a quicker traverse time is of NO material benefit to us for gravity systems.

The brachistochrone solution was sought to find mathematically & experimentally the quickest curved path between two points - the actual quickest method is to drop vertically then just before end height traverse laterally but its not a curve shape.

What is often not realized or completely overlooked, is that AT ANY HEIGHT after initial start height that the velocities/speeds are the SAME - thus, track shape can effect time taken but it can not effect the velocity/speed & hence the Kinetic Energy of a rolling mass.

Therefore the Capacity to do Work [in Joules] of both comparisons is the SAME as their respective Pe's can be retro-calculated from their end height velocities & Ke's, & visa versa.

----------------------------------------

If you could find a way for a traversing mass to, not arrive quicker, but arrive with a faster velocity at end height [not counting losses] you will have found a useful loophole to the gravity wheel physics conundrum & in the process proved the gravity is NOT Conservative as it gives back more than it takes !

[DrWhat]

Yes but on the longer track one wheel (or ball) spins much faster and hence many more times than on the shorter track. If we were to place a dynamo inside each wheel/ball with an LED lighting up, which LED would shine the brightest and for the longest?

[Fletcher]

Kinetic Energy = Rotational Kinetic Energy + Translational Kinetic Energy !

[Grimer]

Frank .. this is essentially a "brachistochrone" problem.

http://curvebank.calstatela.edu/brach77/brach77.htm

It has been discussed on this board many times - try a search for a decent animation & explanation.

---------------------------------------

Surely we must be able to use this in some way to obtain perpetual motion.

Your example shows the start height & end heights the same although the steepness of the track varies - if you think about it a steeper track allows the mass to accelerate quickly due 'g' thus greater mean speed & earlier arrival time.

BUT ..

No Work was Done in physics terms because the start & finish height are the same, so a quicker traverse time is of NO material benefit to us for gravity systems.

The brachistochrone solution was sought to find mathematically & experimentally the quickest curved path between two points - the actual quickest method is to drop vertically then just before end height traverse laterally but its not a curve shape.

What is often not realized or completely overlooked, is that AT ANY HEIGHT after initial start height that the velocities/speeds are the SAME - thus, track shape can effect time taken but it can not effect the velocity/speed & hence the Kinetic Energy of a rolling mass.

Therefore the Capacity to do Work [in Joules] of both comparisons is the SAME as their respective Pe's can be retro-calculated from their end height velocities & Ke's, & visa versa.

----------------------------------------

If you could find a way for a traversing mass to, not arrive quicker, but arrive with a faster velocity at end height [not counting losses] you will have found a useful loophole to the gravity wheel physics conundrum & in the process proved the gravity is NOT Conservative as it gives back more than it takes !

Thanks for that , Fletcher. Very useful.

I can see why this source of energy has been missed. Bit like the equations of state for water vapour really.

I can also see that the claim there is energy to be obtained by taking one line out and returning by the other is going to engender huge dissonance.

Only a physical demonstration will overcome that.

And now I have to be off to take Edwin and George to school.

[Grimer]

Frank .. this is essentially a "brachistochrone" problem. ...

I am well aware of the '"brachistochrone" problem" as you put it.

Indeed, so well aware that I plotted the two curves as cycloids - as you will no doubt recognise from examining their parametric formulae.

I guessed, correctly as it turns out, that someone would bring up that topic.

[Grimer]

Yes but on the longer track one wheel (or ball) spins much faster and hence many more times than on the shorter track. If we were to place a dynamo inside each wheel/ball with an LED lighting up, which LED would shine the brightest and for the longest?

Rotational energy is a side issue. One can eliminate that problem in the case of the video demonstration by using a cars with very small wheels such as the Hotwheel toys. Better still one could use an airbed track where a slider is supported on multiple fine airjets.

[Grimer]

...
What is often not realised or completely overlooked, is that AT ANY HEIGHT after initial start height that the velocities/speeds are the SAME - thus, track shape can effect time taken but it can not effect the velocity/speed & hence the Kinetic Energy of a rolling mass.

Therefore the Capacity to do Work [in Joules] of both comparisons is the SAME as their respective PE's can be retro-calculated from their end height velocities & KE's, & vice versa.

But you are ignoring the jerk energy which are different for the two paths
See:
http://www.besslerwheel.com/forum/viewt ... 4768#84768

You are ignoring a higher order of energy which is equivalent, albeit more subtle, to ignoring energy put in by an electric or magnetic field for example.