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Balancing a pencil

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Rgiose

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Sep 8, 2016, 4:29:48 PM9/8/16
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Balancing a pencil

Consider a pencil that stands upright on its tip and then falls over.

Let’s idealize the pencil as a mass m sitting at the end of a massless
rod of length L

(a) Assume that the pencil makes an initial (small) angle µ1 with the
vertical, and that its initial angular speed is w1. The angle will
eventually become large, but while it is small (so that sin(A) => A),
what is µ as a function of time?

Mahipal

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Sep 8, 2016, 5:08:13 PM9/8/16
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Usenet discussion groups are not for homework assignments. At least,
that was not what unmoderated discussion groups were about. Besides,
how would you gauge which answer was the expected-to-be-correct one?

Ever balance a tennis racquect on your finger while running and spinning?

From {R,G,I,O,S,E} to {S,E,R,G,I,O} is 6!=720 possible permutations.
https://www.google.com/?gws_rd=ssl#q=6! has more interesting details.

Why Sergio are you nymshifting so often? If sci.physics has less than
6 actual active interactors, so be it. We don't need no stinking false
UserIDs Personas to make it appear as if we're a larger audience than
we actually, as publically advertised, as claimed, as experienced, are.

-- Mahipal “IPMM... माहिपाल ७६३८: d(me) != 0 ... me alwa(y)s changes...”

Rgiose

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Sep 8, 2016, 5:10:14 PM9/8/16
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Hint: find component due to gravity, solve for µ'' as general equation,
plug in initial conditions.


the second part of the problem is finding how long balancing can be
maintained, and that is only 3.5 seconds ! which is derrived from
Heisenberg’s uncertainty principle !!

Rgiose

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Sep 8, 2016, 5:30:54 PM9/8/16
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ahhhh....

yes on the 720. But if nymshifting only rotated and maintaining
sequence, only 5, but could be 10 if going reversie was included.
nymshifts is to discourrage NSA and its ilks (Hiellary) from digging
into history, from the future, for future blackmailings.

Hope NSA runs into those executable files that reformat all their hard
drives at once, may they fail like the PMTs at Super-Kamiokande.

NSA Has about 6 centers in the usa (that I know of) that record data,
near power sources, I have seen one of their new servers, (2 years ago)
huge thing, memory for a normal PC is 4 to 16 Gbyte, theirs is a terrabyte.



the problem above is not really homework, actually an easy problem if I
was still doing them, but not. now it is a hard problem.

the second part of the problem is really hard, and says nothing can
balance a pencle more than 3.5 seconds (not spinning)


the problem and answers are available a harvard problem list even
starfarter found the place before, google is your fiend.

Alan Folmsbee

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Sep 8, 2016, 5:59:16 PM9/8/16
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=


That is like a gyroscope falling over, but your length L is replaced by the length traveled per second at the gyro rim:

L = circumference * rpm/60

L = 2 pi r * 2 pi omega

where omega is the angular velocity of the gyroscope. Use a pencil with L = 100 meters to find out how fast a gyro falls over when omega*r = L/4 pi^2

noTthaTguY

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Sep 8, 2016, 7:20:57 PM9/8/16
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secondpower of pi, c00l

Mahipal

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Sep 8, 2016, 9:19:50 PM9/8/16
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On Thursday, September 8, 2016 at 1:30:54 PM UTC-4, Rgiose wrote:
> On 9/8/2016 12:08 PM, Mahipal wrote:
> > On Thursday, September 8, 2016 at 12:29:48 PM UTC-4, Rgiose wrote:
> >> Balancing a pencil
>
> >> Consider a pencil that stands upright on its tip and then falls over.
> >>
> >> Let’s idealize the pencil as a mass m sitting at the end of a massless
> >> rod of length L
>
> >> (a) Assume that the pencil makes an initial (small) angle µ1 with the
> >> vertical, and that its initial angular speed is w1. The angle will
> >> eventually become large, but while it is small (so that sin(A) => A),
> >> what is µ as a function of time?
> >
> > Usenet discussion groups are not for homework assignments. At least,
> > that was not what unmoderated discussion groups were about. Besides,
> > how would you gauge which answer was the expected-to-be-correct one?
>
> > Ever balance a tennis racquect on your finger while running and spinning?
> >
> > From {R,G,I,O,S,E} to {S,E,R,G,I,O} is 6!=720 possible permutations.
> > https://www.google.com/?gws_rd=ssl#q=6! has more interesting details.
>
> > Why Sergio are you nymshifting so often? If sci.physics has less than
> > 6 actual active interactors, so be it. We don't need no stinking false
> > UserIDs Personas to make it appear as if we're a larger audience than
> > we actually, as publically advertised, as claimed, as experienced, are.
> >
> > -- Mahipal “IPMM... माहिपाल ७६३८: d(me) != 0 ... me alwa(y)s changes...”
>
> ahhhh....

Most readers first read the UserID of the posters. Messengers matter.

> yes on the 720. But if nymshifting only rotated and maintaining
> sequence, only 5, but could be 10 if going reversie was included.
> nymshifts is to discourrage NSA and its ilks (Hiellary) from digging
> into history, from the future, for future blackmailings.

Hiellary? That's funny. Don't be afraid, be yourself. If I could
identify you in less than no-time, imagine what 100s of FBI agents
looking through touched-up emails, with like four lines of text each,
max, provided by our beloved TrumpET BlowsJobs to Czar Putin, can do.

By no-time, I mean less than a commercial break, tweet, or news cycle. Combined!

Just imagine 1000s of FBI/NSA/MI5/KGB/CIA/TLA/... agents all snooping
through their @#smartestphones, their iWatches, sipping their sweet
Starbucks lattes, ... all the while pretending to have deciphered
encrypted tweets. In the meantime, winking at the FitBit Girl|Boy...

Perhaps I ought write TV commercials? Maybe I watch too many? Oye ve!
Music, James Bond style music, goes into fishy ears hearing babbling...

> Hope NSA runs into those executable files that reformat all their hard
> drives at once, may they fail like the PMTs at Super-Kamiokande.

More details please Sergio. I did read a bit regards Super-K.

> NSA Has about 6 centers in the usa (that I know of) that record data,
> near power sources, I have seen one of their new servers, (2 years ago)
> huge thing, memory for a normal PC is 4 to 16 Gbyte, theirs is a terrabyte.

I've worked with a few server farms, none as vast as NSA might admit having.

> the problem above is not really homework, actually an easy problem if I
> was still doing them, but not. now it is a hard problem.

That's a very good point, SergioJi. Time makes me forget stuff too.

> the second part of the problem is really hard, and says nothing can
> balance a pencle more than 3.5 seconds (not spinning)

That's a bold statement. Demonstrate this time-limit.

> the problem and answers are available a harvard problem list even
> starfarter found the place before, google is your fiend.

Notice how Google/Alphabet has long forgot their 'Do Know Evil' motto?

noTthaTguY

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Sep 11, 2016, 4:50:17 PM9/11/16
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or, pi*2*d*pi*(angular velocity/cycle)

john

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Sep 11, 2016, 6:40:01 PM9/11/16
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Egg-balancing day is the only
time you can balance a pencil on its point
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