Re: [Phys-l] g...

["James S. Marsh" <jsmarsh@uwf.edu>]

I like the idea of letting the students measure g and using that  
value, and for the
following reason.

I claim to be the first person to ever measure the value of g on the  
moon, live, in
living color, and with stereophonic sound.  Well, maybe the  
stereophonic sound
is stretching it a bit.

You will remember that when Commander Shephard was cavorting around  
on the
moon, he had brought a length of rope with him one end of which he  
tied to one of
the rungs of the ladder.  To the other end he tied a...hammer I  
believe it was.
And when he would return to the lander ever and anon he would poke  
the hammer
and it would swing at the end of the pendulum.

So here I am with a bunch of colleagues in a local bar, sipping on  
beer and watching
these proceedings on the TV.  They were being telecast live from the  
surface of the moon.

The period of the pendulum was easily measured and I got a pretty  
good measurement.
I had to estimate the length of the pendulum which I did by comparing  
it with Shephard's
height.  This I estimated to be about seven feet since he was dressed  
up in that space suit.
Hence the measurement of g on the moon.

I like to modestly share this story with my students when we are  
discussing the measurement
of g using a pendulum.

I've always had the urge to acquire a tape of that moon expedition to  
show the students and
to ask them, "What, therefor, is the value of g on the moon?"  It  
would be a dandy lab experiment.

James S. Marsh
Pensacola, FL

On Nov 19, 2006, at 10:17 PM, John Clement wrote:

> According to:
> http://curious.astro.cornell.edu/question.php?number=310
>
> Taking into account both of the above effects, the gravitational
> acceleration is 9.78 m/s2 at the equator and 9.83 m/s2 at the  
> poles, so you
> weigh about 0.5% more at the poles than at the equator.
>
> Now what is meant by conform?  I would assume that you would tell  
> students
> that "they have to use 9.81 even though this is not strictly  
> true".  I would
> be tempted to say that this what the NYS Regents voted on as the  
> official
> value, and that they probably did not bother to measure it.  It might
> actually be that value in parts of NYS, but probably not in  
> Houston.  Should
> we have a Southern value and a Northern value?  Should we have one  
> for each
> state?  Hmmmmmmm.  Do the blue states have different values from  
> the red
> ones?  Yes, I do know that Regents exams are regraded by the  
> central office,
> or at least they used to be.
>
> BTW one source claimed a value of 9.87 (where???) which would not  
> even round
> to 9.8.  I let students measure it and they find it is about 10,  
> which is
> the value we then proceed to use.
>
> John M. Clement
> Houston, TX
>
>
> > > On Sun, 19 Nov 2006 08:13:29 -0500 "R. McDermott" <rmcder@gmail.com>
> > > writes:
> > > > I introduce g as the strength of a  gravitational field due to the
> > > Earth, remind them that it varies
> > > > with  distance, etc, and has a value of 9.81 N/kg at the Earth's
> > > surface.
> > >
> > > If you wrote that g has a value of 9.8 N/kg at the Earth's surface,
> > > I would agree. But is it correct to add the additional significant
> > > figure  and make it 9.81 here??
> >
> > NY State syllabus (and reference table) now gives it as 9.81, not  
> > 9.8 as
> > in
> > previous years.  We are obliged to conform.
>
>
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