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Author Topic: The pendulum bias paradox experiment  (Read 25628 times)

Tusk

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The pendulum bias paradox experiment
« on: November 04, 2012, 01:58:28 PM »
Hi all, my name is Steven C. Ross and this is my first post at overunity.com. This is a simple little experiment - easily replicated - the conditions for which I extrapolated from known phenomena. However, as I haven't seen it around my guess is that the elements haven't been put together in this way before, but I can't say with any certainty. The short video is at the following web address, be sure to view it to the end or you could miss the paradox:

http://www.youtube.com/watch?v=wjzKIE6m02w&feature=youtu.be

As the experiment demonstrates, conventional perceptions of energy regarding (at least) mass in motion are fundamentally flawed due to their dependance on frame of reference. The motion of the centre of mass of the two ball & block systems through our 'static' frame of reference dictates the outcome of each collision with results apparently at odds with the initial equilibrium condition of the two ball system, in which the centre of mass is static in the observer's frame of reference. Since momentum is the 'parent' phenomena, that is to say the collision outcome is determined by momentum (the motion of the centre of mass of the system is unaffected by the collision within the system) then any general perceptions of 'energy exchange' must be based on frames of reference. This of course is already known, but just seeing it written down is no substitute for actually watching the phenomena unfold.

Personally I found it refreshing to witness the phenomena in such a way as to make it very clear that energy, at least kinetic energy, far from being absolute, is simply variable and dependent - literally - on your point of view.





     







Tusk

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Re: The pendulum bias paradox experiment
« Reply #1 on: November 08, 2012, 04:56:00 AM »
Wow tough crowd. I guess that's the problem with a paradox. If anyone wants further explanation on this one feel free to drop me a line.

MileHigh

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Re: The pendulum bias paradox experiment
« Reply #2 on: November 08, 2012, 05:15:14 AM »
I looked at your clip and I don't see any paradox.  I saw wooden the block move different distances depending on which ball hit the block, but so what?  Is that what you are suggesting is the paradox?  Nothing looked unusual to me.

Tusk

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Re: The pendulum bias paradox experiment
« Reply #3 on: November 08, 2012, 03:18:44 PM »
Quote
Nothing looked unusual to me.

Thanks for your reply MileHigh. Perception is everything. Someone (presumably like yourself) with a good grasp of basic physics would certainly understand why the small ball (having significantly more kinetic energy than the large ball) does not dominate in the collision. To the untrained eye however, the balls appear to have equal energy in the two ball collision, yet the ball and block collisions demonstrate that this is certainly not the case.

No paradox can survive it's own solution. To those familiar with the phenomena I offer my apologies.

 

Tusk

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Re: The pendulum bias paradox experiment
« Reply #4 on: November 10, 2012, 04:59:44 AM »
Ok I'll come back another notch; my previous comment was one of gentle sarcasm, apparently to no avail. Perhaps a direct approach then.

In order to dispel the paradox it is necessary to explain - beyond a simple reference to the disparities of momentum and kinetic energy - why in the two ball collision the small ball (which has the greater kinetic energy) does not dominate the collision. Not recognising the paradox merely indicates an 'off the shelf' perception based on conventional dogma. (hint - statements like 'one collision is inertial while the other is non-inertial' explain nothing)

Why does the ball with greater kinetic energy not dominate?

I was led to believe this was the right place for the examination and discussion of unconventional ideas. There's more where this came from but I'm going to need a little more to work with than indifference.

 



 


Newton II

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Re: The pendulum bias paradox experiment
« Reply #5 on: November 10, 2012, 02:44:07 PM »

Why does the ball with greater kinetic energy not dominate?



I didnot understand your question.   What I see from that expereiment is that,  the bigger ball will rise to lesser height because of its weight hence it moves through lesser distance in arc path.  The smaller ball rises to higher height because of its lesser weight hence moves through longer distance in arc path.   

The potential energy gained by both the balls will  be equal  m1*g*h1  = m2 *g*h2.      If you use both the balls of same size,  they will be displaced to equal distance.

TinselKoala

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Re: The pendulum bias paradox experiment
« Reply #6 on: November 11, 2012, 03:35:10 AM »
Momentum, mv, is conserved.
There is also a difference between elastic and inelastic collisions in the demonstration, as well as the matter of the stiction of the block being a function of impact velocity. These complications may be considered similarly to the issue of impedance matching in electrical transmission lines. In fact, there is a mechanical impedance mismatch between the swinging ball and the resting block, and the magnitude of this mismatch is different for the two different balls, which hit the block with the same _momentum_ but with different velocities.
I guess.

MileHigh

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Re: The pendulum bias paradox experiment
« Reply #7 on: November 11, 2012, 05:12:34 AM »
Thanks for your reply MileHigh. Perception is everything. Someone (presumably like yourself) with a good grasp of basic physics would certainly understand why the small ball (having significantly more kinetic energy than the large ball) does not dominate in the collision. To the untrained eye however, the balls appear to have equal energy in the two ball collision, yet the ball and block collisions demonstrate that this is certainly not the case.

No paradox can survive it's own solution. To those familiar with the phenomena I offer my apologies.

When the balls are first released, they in fact do have approximately the same amount of kinetic energy.   So you are making an incorrect assumption.  So perhaps the illusion of the paradox is a bit more complicated than you thought?

Tusk

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Re: The pendulum bias paradox experiment
« Reply #8 on: November 11, 2012, 02:13:53 PM »
Good effort TK, hopefully you won't object to me doing an analysis of your response:

Quote
Momentum, mv, is conserved.

As it should be, under all circumstances. I will be breaking a law of physics later, but not this one.

Quote
There is also a difference between elastic and inelastic collisions

True but this doesn't affect the outcome in terms of the paradox. Substituting another ball suspended by pendulum (in place of the block) gives a similar result.

Quote
there is a mechanical impedance mismatch between the swinging ball and the resting block, and the magnitude of this mismatch is different for the two different balls

Am I correct in assuming you have an electrical or electronic engineering background? Anyway it's a fair comment but again, we can just substitute a ball for the block.

It might be helpful to run a little thought experiment at this point. Allow that a ball is struck hard with a bat (cricket or baseball) next to a railway line as a train goes past. Allow that both the ball and the train are moving at the same velocity and in almost the same direction, but the ball converges with the train and enters a carriage through an open window. Inside the carriage the occupants observe the ball seemingly float in mid air as it reaches it's apogee then drop to the floor where it remains at rest.

Disregarding air resistance (for simplicity) quantify the kinetic energy of the ball. Not literally, just consider the problem and how it relates to the pendulum result.

 



 




DreamThinkBuild

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Re: The pendulum bias paradox experiment
« Reply #9 on: November 11, 2012, 02:52:51 PM »
Hi Tusk,

Welcome to the forum. Thanks for sharing your experiment.

Hi TinselKoala,

Something you said about impedance matching bought up this paper I read recently.

AN ALGORITHM FOR THE HYPERVELOCITY LAUNCHER SIMULATION OF HIGH-LOW DENSITY FLYER PLATES

http://jeacfm.cse.polyu.edu.hk/download/download.php?dirname=vol3no4&act=d&f=vol3no4-4_BaiJS.pdf

A rubber ball is essentially a graded surface as you go to the core the material density/impedance changes. I do not know if this is relevant to this pendulum experiment but it's an interesting effect.

TinselKoala

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Re: The pendulum bias paradox experiment
« Reply #10 on: November 11, 2012, 08:36:18 PM »
Ok I'll come back another notch; my previous comment was one of gentle sarcasm, apparently to no avail. Perhaps a direct approach then.

In order to dispel the paradox it is necessary to explain - beyond a simple reference to the disparities of momentum and kinetic energy - why in the two ball collision the small ball (which has the greater kinetic energy) does not dominate the collision. Not recognising the paradox merely indicates an 'off the shelf' perception based on conventional dogma. (hint - statements like 'one collision is inertial while the other is non-inertial' explain nothing)

Why does the ball with greater kinetic energy not dominate?

I was led to believe this was the right place for the examination and discussion of unconventional ideas. There's more where this came from but I'm going to need a little more to work with than indifference.

Is this, then, the statement of your "paradox"?

Either I am not understanding you (along with Mile High and NewtonII) or you are not understanding the full situation you are describing.
I can tell you that I do have somewhat of an EE type background, but I can also tell you that I spent years in the laboratory investigating a set of phenomena involving projectile impacts, transfers of momentum, and kinetic energy (the Graneau water arc experiments) and I believe that my understanding of these phenomena is .... adequate for the present task.
If I am seeing and interpreting your demo correctly, you are saying that the fact that the wooden block moves different distances when struck by each ball, which presumably have the same KE at the point of impact, is a "paradox", since  conservation laws would predict that the block of wood should move the same distance if it is receiving the same "energy" or momentum transfer from the two differently sized balls. I mentioned sticktion, which unlike mere sliding friction, IS related to the initial impact _velocity_, and I mentioned the effects of inelastic collisions on momentum transfer, and I mentioned mechanical impedance mismatch, which is really a description not a reason.

Now... to improve your demo, let's take the trig out of the system, and instead of bringing the two balls out to corresponding _horizontal_ distances, let's bring them (their centers) to corresponding VERTICAL heights.... since this height is what determines the GPE and also the final horizontal velocity of the balls at bottom dead center, where the impact with each other or the wooden block should occur. This vertical height will also be easier to measure; I'm sure I don't have to tell you how to put two ruled sight gauges next to the apparatus and how to indicate the Centers of Mass of the balls against the vertical line gauges.
I'll accept your manual release method as valid, although it would be easy enough for you to rig a simultaneous, mechanical release system.
But let's take the wooden block and put it on some freely-rolling wheels, to reduce the contribution of sticktion, and let's bond a hard striking target to it, and let's be sure to use completely elastic balls... steel ball bearings are a great choice. Now we have better controls on input energy, we have moved towards assuring elastic collisions, and we have reduced the effect of sticktion which is velocity dependent.
Once you've done all of this and repeated the experiment, and you still get a little difference in the distance the block travels... we can see if we can eliminate other causes for the data you see. We may even arrive at the point where we have to consider shock waves travelling through the wooden block as energy dissipative mechanisms. But I doubt if the thread will last that long.

TinselKoala

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Re: The pendulum bias paradox experiment
« Reply #11 on: November 11, 2012, 08:41:01 PM »
@DTB: thanks for that..... it is indeed an illustration of a mechanical impedance-matching system, whose effect is to maximize the transfer of KE from the driver to the "flyer".... which I'd call a projectile or even a bullet. It certainly is relevant because it illustrates that the energy transfer is dependent on the elasticity of the collision as well as the time over which the force of impact is applied. The "impactor" is like the balls and the "flyer" is like the wooden block. The amount of energy transferred by an impactor with the same initial KE in a given collision depends strongly on the temporal dynamics and the energy dissipated in the collision itself thru deformation, sound, and even spalling of material.

Tusk

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Re: The pendulum bias paradox experiment
« Reply #12 on: November 12, 2012, 05:56:35 AM »
Interesting that a simple experiment which brings together two known and established outcomes (albeit typically not demonstrated together) causes a focus on the experimental method rather than the results. You can conduct this experiment on the back of an envelope with confidence, the only element requiring attention has already been highlighted.

In the two ball collision, why does the ball with greater kinetic energy not dominate?

I am all out of hints and clues. Try reading my OP. There is nothing new here except what is hidden in plain sight.



MileHigh

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Re: The pendulum bias paradox experiment
« Reply #13 on: November 12, 2012, 06:11:35 AM »
From what I see the balls have equal kinetic energy.

The slower ball more or less pushes the wooden block along and a lot of the energy is burned of in the dynamic friction between the wooden block and the surface.  The assumption being the slower you move the block the more dynamic friction there is.

The faster ball has a partially elastic collision with the block and the block moves faster over the surface and moves farther.  You can see how the ball keeps moving, so not all of the energy of the ball gets transferred into the wooden block.

I don't see any paradox or anything special.

Pirate88179

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Re: The pendulum bias paradox experiment
« Reply #14 on: November 12, 2012, 07:15:04 AM »
Interesting that a simple experiment which brings together two known and established outcomes (albeit typically not demonstrated together) causes a focus on the experimental method rather than the results. You can conduct this experiment on the back of an envelope with confidence, the only element requiring attention has already been highlighted.

In the two ball collision, why does the ball with greater kinetic energy not dominate?

I am all out of hints and clues. Try reading my OP. There is nothing new here except what is hidden in plain sight.

Simple.  The kinetic energy of the 2 balls is equal.  F=MA.  I have no idea what you are getting at here.

Bill