Thursday, October 9, 2014

The Immovable Center

Was reading Asimov’s readable textbook Understanding Physics last night and came upon this tidbit for the first time ever:

“A point on the rim of a turning wheel is moving at a certain speed, a point closer to the center of the wheel is moving at a smaller speed, and a point still closer to the center is moving at a still smaller speed.  The precise center of a turning wheel is motionless.” (Book I, chapter 6)


Can that be true?

I suppose so, if you consider the center as a pointless, dimensionless idealized location.  But in practicality, I would think not.  Even a dot a millimeter in size would revolve.  So would one a billionth of a billionth of a billionth of an angstrom.  Or would it?  That’s an awfully, awfully, awefully small size – angstroms are typically used when talking about measurements within the atom.  And at a billionth of a billionth of a billionth of that, you’re messing with sizes smaller than an electron, much much smaller, so quantum weirdness (is it a wave or is it a particle?) takes effect and things are not what they seem to us up here in Macro World.

So, yeah, maybe when you shrink that point small enough, it does stop spinning with the rest of the disk.  (Though my intuition still balks at this.)

But my new question is – at what size does this happen?  Where is the boundary between motion and motionlessness?

I need to subscribe to a physics magazine and write a letter to an editor!

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