Re: What keeps electrons spinning around their nucleus?
From: PD (pdraper_at_yahoo.com)
Date: 03/28/05
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Date: 28 Mar 2005 11:33:35 -0800
TomGee wrote:
> Wormy, Bilge, PD, and all you other lemmings,
>
> you cannot understand that it is the _measurement_ of the force which
> is fictional and not the feeling of being pulled out as a carousel
> spins. You cannot make the force disappear just by invalidating your
> own measurements. You should not think that websites are the
ultimate
> authority on anything, either, as subjective opinion runs rampart all
> through it. You will learn that, Bilgy, when if ever you get to the
> fifth grade.
>
> TomGee
One more little experiment, Tom, on your carousel. Take your
pocketwatch on the carousel with you and hang it by its chain between
your thumb and forefinger. If you don't have a pocketwatch, take your
wristwatch and hang it by a string in the same way. Now have someone
spin you up on the carousel.
You see the watch swings outward on the chain. Why, you ask? Is it
centrifugal force? No, your fourth grade teacher says, look again. The
watch must go in a circle, too, if it is to follow you around on the
carousel, right?
Right, you say.
And there must be a force that makes the watch go around in a circle,
because if there were no force, the watch would go in a straight line,
right?
You frown and say, umm, that has something to do with Newton's laws,
doesn't it?
Your teacher throws you a Jolly Rancher candy and says, right! And that
force must be supplied by what?
You frown again and say, gee, I dunno.
Well, your teacher prods, what's acting on the watch?
Umm. Gravity?
OK, your teacher nods, but that's pointed down and can't be pulling the
watch around the center of the circle, can it?
No, I guess not, you say. But the only other thing attached to it is
the string!
Precisely! your teacher beams. And strings can only pull along their
length, right? So if the string were to remain hanging vertically, it
would not be able to provide a horizontal force inward toward the
center of the circle, could it?
I guess, you say scowling.
So you see, your teacher concludes, the string *must* be tilted that
way to provide the centripetal force inward on the watch required to
get it to move in a circle. The horizontal piece of that string's
tension is what provides the centripetal force, and the vertical piece
of the tension is what opposes gravity. Remember that there is nothing
present that can push on the watch outward -- the string can only pull.
But...but... what balances the inward force?! you protest.
Nothing, your 4th grade teacher reminds you. The watch is not in
equilibrium. The forces need not add to zero. If it were in
equilibrium, it would be moving in a straight line at constant speed,
and it's clearly not doing that.
But by now you are nauseous and not particularly interested in the
Jolly Rancher or, for that matter, in physics, despite the wonderful
little lesson you learned at the playground today.
PD
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