Tube Race: Newsletter Challenge (July 2013)

So, basically, it is as if you were rolling a ball from each end of a concave surface with no friction,as in a vacuum with magnetic levitation.Each ball would naturally,and logically go toward the lowest point.But,because there is no friction, the enregy does not decrease, and there is exactly enough energy to reach the other side, and no more.It stops,then repeats the cycle.

The only possible losses I see in the above scenario is the mutual gravitational attraction(not friction, in the purest sense) between the objects (
They do have mass) that would eventually cause them to collide and stop.)Or would they! Perhaps they would just spin forever?

In real life,if you were to suspend two pendulums from the top of their arc,and let go,they would never quite get back to where they started, and eventually they would cease to move at all.

I saw a real life demonstration of this at my university.An anvil was pulled back from it's resting point, and the professor asked if anyone truly believed in physics.A volunteer was selected, and the anvil was pulled back to his nose and released.The test was whether you moved your head or stayed put when the anvil returned in it's arc.

A lot of students stepped back.I stayed put.

At least,that is the way I see it, and it does not violate common sense or logic.

^{What you say is right, so this is really nit-picky, but here goes.....}

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'...you were rolling a ball from each end of a concave surface with no friction...'

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Without friction, a ball wouldn't really 'roll' in the proper sense.

Ok, you want to nit-pick?

"Rolling" in this case, implies that a rotation was imparted prior to release of the ball."Dropping" implies no prior rotation of the ball.

If you wish to nit pick your balls, go right ahead, but do it in private.(And be careful of the crowd you run with)

OK, the ball's now on your side of the nit(ahem! Net).

Note: For those of you unfamiliar with the term, I offer this definition from Wikipedia:

Nitpicking is the act of removing nits (the eggs of lice, generally head lice,(but sometimes the genital area) (aka;Crabs) (Emphasis mine) from the host's hair. As the nits are cemented to individual hairs, they cannot be removed with most lice combs and, before modern chemical methods were invented, the only options were to shave all the host's hair or to pick them free one by one.

This is a slow and laborious process, as the root of each individual hair must be examined for infestation. It was largely abandoned as modern chemical methods became available; however, as lice populations can and do develop resistance, manual nitpicking is still often necessary.

Ahem,

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As it was not dislodged by my initial gentle nudge, I will continue to pick at this nit, lest it survive to become a full fledged louse. The ((k)nitted?) gloves are off!

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'Rolling' is not commonly defined as you suggest: rotation imparted prior to release.

I never hear people talk about a baseball pitcher 'rolling' the ball so that it will curve. The Earth is not said to be rolling along its orbit.

The bouncing damn-bursting bombs of WWII are not described as (back) rolled to facilitate bouncing across the water.

A rifle is not said to roll a bullet for purposes of stability.

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'Rolling' refers to a condition where there is an area of contact in which there is minimal sliding (i.e. at any particular instant, the portion of the rolling object in contact with the surface is not in motion with respect to the surface to any great degree) and at points along a line normal to the contact surface, the speed of the object at that point relative to surface increased with the distance away from the area of contact.

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While a ball may certainly be 'rolled' off the hand to impart rotation prior to release, 'roll' in this case pertains to the action of the ball in contact with the surface of the hand, not the imparting of rotation.

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If there were no friction, the requisite torque to initiate rolling would be absent.

<sigh>

Note in your "spring force: accleration equation here m, the mass of the object(s) has cancelled out. Yet when you show this statement somehow the object mass m has re-appeared. I am quite sure that mass of the object does not affect gravitation harmonic acceleration.