Re: accruate "sundials"

In article <H6due.11419$5u4.36175@xxxxxxxxxxxxxx>,
jtaylor@xxxxxxxxxxxxxxxxxxxxxxxxx says...

>"Paul Schlyter" <pausch@xxxxxxx> wrote in message
>news:1119439990.cc3bcd73dd3081fcbb10e7671777428b@xxxxxxxxxxx
>>> Yes, please, would someone tell me how we could measure this rotation
>>> without refernce to any other body?
>>
>> Actually, there is a way to do that: measure the coriolis force of a
>> body which moves on a surface. The surface must be horizontal and
>> smoot, and the body must be a sphere. Preferably the experiment should
>> be conducted in a vacuum. And the experiment should be performed at a
>> high latitude - ideally at the north pole, but in practice 40-60 deg
>> latitude will do. The measured rotation rate will be the vertical
>> component of the rotation vector, whose magnitude is the rotation rate
>> multiplied with the sine of the latitude.
>
> Are you sure this is correct?
>
> I am no expert on the Coriolis effect, but if you had the earth in space as
> it is, rotating relative to the sun, and then suddenly, by some magical
> means, removed EVERYTHING but the earth from the universe, would the
> Coriolis effect still be observed?

Neither I nor anyone else knows this of course, since nobody has been able
to perform this experiment.... :-)

But as long as there's inertia, there will be a coriolis force, as well as a
centrifugal force, in a rotating frame of reference.

So what you're really asking is this: if EVERYTHING but the Earth was
removed from the universe, would there still be inertia in anything having
mass?


However, you changed subject here. The question was "would someone tell me
how we could measure this rotation without reference to any other body?".
And, yes, there's a way to do that, by measuring the Coriolis force. And
this can be done in a closed and sealed room, where the observer has no way
to use external bodies as a reference.

Compare this to the same closed and sealed room, where it is impossible
to determine if the room is situated in a gravitational field, or if the
room is smoothly accelerating. That's a difference.



--
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at saaf dot se
WWW: http://stjarnhimlen.se/
.

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