The pendulum bias paradox experiment

[Fester]

The base plate of this pedulum rig is poor at best. It needs to be done with a single piece of wood. The secondary piece for the block test might not be the same thickness. This will leave gaps and reduce friction. This will mean less friction for the small ball test and not the big ball test. A small lip or even a crack could change the results as well. Also get rid of the elastic rubber balls and get steel balls. Energy transfer for elastic materials is directly effected by their density. Your big ball could have a large air pocket inside of it. It may have the same mass but its may have a bias of density opposite the end your string is on. Which would make the side wall of the ball collapse more than it "should". The spring rate of the ball is going to be how much energy it stores up for the second swing. Hence, part of the kenetic energy is turn back into potential energy. So your rig as a measure of kenetic energy is inadequate because of the rubber balls you use.

You cannot get static results from a non-static environment. The environment in the video is under change from have 2 different base plates and 2 different flexibility rates of the balls. A poor rig giving innacurate results. Ego's do need checked sir, that would be yours. It's one thing to think you have something based on a "shoddy" rig at best, but to plague a students mind with it is not responsible. Your appearant misconception can stick with that student for a long time.

[Tusk]

The base plate of this pedulum rig is poor at best. It needs to be done with a single piece of wood.

Thanks for the advice re increasing experimental rigor Fester. If there was any doubt about the outcome I would certainly have adopted such measures, but since the results as shown are already known and predicted in the literature it seemed acceptable to present an apparatus capable of reproducing those results for demonstration purposes rather than a research grade apparatus. If anyone still has concerns I would refer them to the relevant chapters on momentum and kinetic energy of any decent high school physics book.

There is indeed a noticeable error in the motion of the block when struck by the small ball, it should show a four fold increase over the large ball and block test, but in fact only moves approximately X 3 which really doesn't impact on the spirit of the demonstration. None of the points you mention apparently had any significant effect on the results, which as I have already stated on several occasions are predicted in the literature and furthermore present little difficulty in the calculation.

If the local temperament is more for finding fault in the minutia than checking for authenticity in the main thrust of an idea and attempting to understand the reasoning behind it then perhaps after all I am in the wrong place.

[Newton II]

Actually the kinetic energy of the small ball = 4 x kinetic energy of the large ball.

If kinetic energy of small ball is 4 times more than that of large ball, then after each collision the energy of both balls should go up and oscillations should become perpetual even after considering losses.  Is it not?

[TinselKoala]

@Tusk: I see you have chosen Option A: you repeat the same phrase, only louder.


I explained one interpretation that shows that the smaller ball "does dominate". I could also explain an interpretation of your phrase that shows that the larger ball "dominates", or that neither "dominates".... because you do not specify what you mean by your phrase in a physical (I mean physics, kinematics, dynamics, mathematics) context. You choose to play word games instead of asking a real question that can be answered with vector calculus. You want there to be a paradox where there isn't one, or you want people to see or think there's a paradox, because you have some point that you are going to be making, down the road, and you want people to be trapped into accepting it because of your "logic" at this stage of the matter.

Fine, I'm sure you'll find plenty of people to play your game. Carry on.... but please, you could at least stop being so very predictable.

[Tusk]

I'm sorry you see it that way TK, I was merely attempting to avoid obfuscation of the fundamental principles in play here by getting bogged down in the maths. We really don't need to dot all the I's and cross all the T's at this stage of reviewing established material - the simple fact that we can arrange a collision between two bodies with different kinetic energy which results in the total mass of the system being brought to a complete state of motionlessness at the very centre of mass of the system is not even in question, it is already known. We can see this happening clearly in the experiment, and already know that the small ball has higher kinetic energy than the large ball (if not from the ball on block tests then by simple observation of relative mass and velocity).

The issue of dominance in the collision seems to me self explanatory, but perhaps I can state this another way for clarity; let's assume a totally non-elastic collision between two balls of clay with the same mass and velocity as in the experiment. Since in the elastic collision the balls cease all motion then reciprocate at the bottom of the pendulum (as it happens this is also the location of the centre of mass of the two balls) we can assume with confidence that the clay balls will come together and remain motionless at this same point.

If the balls represented sumo wrestlers then it would be fair to say that neither ball dominated. If we allowed the balls to represent an arm wrestling bout then again, neither ball dominated. If the balls represented two bulls rushing headlong at each other during combat then again, neither could be said to dominate.

Only if the balls in this inelastic collision were still in motion post collision could we then say that one ball had dominated. Going back to our elastic collision we would say that if the point of collision moved in subsequent collisions, then one ball had dominated.

But I find it hard to believe that someone of your experience could repeatedly fail to see the blindingly obvious. More likely you are simply unable to answer the question, in which case you are now too heavily invested in 'winning' this exchange to admit that a genuine phenomena is in play here which requires explanation. No doubt you would prefer the discussion to deteriorate into a dry mathematical analysis, but I refuse that challenge and for good reason. If the discovery of overunity was possible by mathematics alone we would have it already. Only by an open minded re-examination of known phenomena using careful observation and the gift of logic can we hope to uncover those aspects of the phenomena which will lead us to a full understanding of reality yet which have to this point in time eluded us. So I ask yet again...

Why does the ball with greater kinetic energy not dominate?

(and for TinselKoala, by special request)

Why does the ball with greater kinetic energy not disturb the centre of mass of the system, which is static throughout the experiment?