Re: NASA suffers from windows...

In article <znu-F62813.00283529072005@xxxxxxxxxxxxxx>, ZnU <znu@xxxxxxxxxxxx>
wrote:

> In article <dlhGe.7935$_%4.7179@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
> "ed" <news_test@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> > In news:znu-AC9937.22304728072005@xxxxxxxxxxxxxx,
> > ZnU <znu@xxxxxxxxxxxx> typed:
> > > In article <j1gGe.7906$_%4.5746@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
> > > "ed" <news_test@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > >> In news:timberwoof-F45159.13364328072005@xxxxxxxxxxxxxxxxx,
> > >> Timberwoof <timberwoof@xxxxxxxxxxxxxxxxxx> typed:
> > >>> In article <1122573578.565619.87380@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
> > >>> "ed" <news@xxxxxxxxxxxxxxx> wrote:
> > >>>
> > >>>> ZnU wrote:
> > >>>>> In article
> > >>>>> <1122565122.350433.215920@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, "ed"
> > >>>>> <news@xxxxxxxxxxxxxxx> wrote:
> > >>>>>
> > >>>>>> Timberwoof wrote:
> > >>>>>>> In article <W8 Fe.7652$ %4.4827@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
> > >>>>>
> > >>>>> [snip]
> > >>>>>
> > >>>>>> no, it actually doesn't. oh, here you go, from that same site:
> > >>>>>> http://www.kernelthread.com/software/ams/
> > >>>>>> "It is interesting to note that the accelerometer in the
> > >>>>>> PowerBook is calibrated to read (0,0,0) when the laptop is in
> > >>>>>> freefall in a vacuum. In practice, all AMSs may not be
> > >>>>>> calibrated perfectly, or equally. Thus, x and y values may not
> > >>>>>> be zero in a perfectly "stable" position."
> > >>>>>>
> > >>>>>> look at that. just what i said. oh, and by the way, that's not
> > >>>>>> a particularly interesting note, since that's pretty much how all
> > >>>>>> accelerometers work.
> > >>>>>
> > >>>>> Sure, that's how accelerometers work. What you *don't* know is
> > >>>>> what the
> > >>>>> *programming* is. Maybe the machine is programmed to park the
> > >>>>> heads in response to sudden changes in acceleration over a certain
> > >>>>> threshold. On the other hand, maybe the machine is programmed to
> > >>>>> park the heads when the accelerometer reads something close enough
> > >>>>> to (0,0,0), on the assumption that this means it's in the process
> > >>>>> of being dropped.
> > >>>>
> > >>>> no znu, (0, 0, 0) reads stable (as explicitly stated in the
> > >>>> article)- whether sitting on the desk, or in free fall.
> > >>>
> > >>> That's not what the article said.
> > >>
> > >> sure it is.
> > >
> > > No, it's not. It's also not true. Sitting on a level surface, my 12"
> > > PowerBook registers (0,0,54).
> >
> > well shoot, if the article is incorrect about what the accelerometers are
> > doing, they're clearly using a different type than what i'm talking about.
>
> I'm trying to imagine a physical device that directly detects changes in
> acceleration. Sure, it's easy enough to spot changes in acceleration by
> measuring your acceleration now, and comparing that with a reading you
> took previously, but how would you detect changes in acceleration
> *directly*? What force would such a device measure?

Neat puzzle.

Measuring acceleration is not so hard. Build a capacitor so that one of the
plates can move against a spring. Then build an oscillator that uses the
capacitor. When it's oriented so that the plates of the capacitor are closer
together, the oscillator will run at a higher frequency. Turn it over and the
oscillator runs more slowly. Now set up three of them on mutual right angles.
That measures acceleration directly. It is an accelerometer.

In our universe, both speed and acceleration have instantaneous meaning. Speed
you can detect by doppler shift of a distant light source. Acceleration you can
detect by the static compression of a spring with a weight on it. Jerk would be
the change in position of a weight on a spring ... over time. I suppose if you
could measure Doppler shift carefully enough...

--
Timberwoof <me at timberwoof dot com> http://www.timberwoof.com
If Macintosh is a luxury cruise ship,
then Linux is a freighter with wood paneling in the officers' quarters.
.

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