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dseppala@austin.rr.com
science forum Guru Wannabe

Joined: 13 Sep 2005
Posts: 154

Posted: Sat Jul 15, 2006 11:24 pm    Post subject: Clock Properties

In Einstein's paper On The Electrodynamics of Moving Bodies he states
that pendulum clocks don't behave the same way as other clocks.

I don't understand why physicists believe all clocks except pendulum
clocks share the same properties in terms of running at different
rates in different inertial frames. What property does every other
entity have measures time have that pendulum clocks do not and vice
versa.

Thanks,
Dave Seppala
Tom Roberts
science forum Guru

Joined: 24 Mar 2005
Posts: 1399

Posted: Sat Jul 15, 2006 11:39 pm    Post subject: Re: Clock Properties

David wrote:
 Quote: In Einstein's paper On The Electrodynamics of Moving Bodies he states that pendulum clocks don't behave the same way as other clocks.

This depends on what one means by a "pendulum clock". In common usage, a
pendulum clock consists of a box in which a pendulum swings, plus a
mechanism to count those swings. Unfortunately, this is not the complete
clock -- it depends inherently on the earth's gravitation for its
operation, including its tick rate. In freefall such a pendulum clock
does not work at all, and on top of a mountain it ticks more slowly than
at sea level, and in an airplane its tick rate varies wildly as the
plane maneuvers.

To be considered as a clock in the sense physicists use the word, one
must include the pendulum's relationship with the gravitational source.
This makes it impractical to use for most investigations of clock tick rate.

 Quote: I don't understand why physicists believe all clocks except pendulum clocks share the same properties in terms of running at different rates in different inertial frames.

This is not mere "belief", this is an experimental observation. So only
theories that predict such behavior are valid.

 Quote: What property does every other entity have measures time have that pendulum clocks do not and vice versa.

All the other clocks that we normally think of (in this context, anyway)
are self contained, and their tick rate is not directly dependent on any
external quantity; that is NOT true for the pendulum "clock".

Tom Roberts
Sue...
science forum Guru

Joined: 08 May 2005
Posts: 2684

Posted: Sat Jul 15, 2006 11:50 pm    Post subject: Re: Clock Properties

David wrote:
 Quote: In Einstein's paper On The Electrodynamics of Moving Bodies he states that pendulum clocks don't behave the same way as other clocks. I don't understand why physicists believe all clocks except pendulum clocks share the same properties in terms of running at different rates in different inertial frames. What property does every other entity have measures time have that pendulum clocks do not and vice versa. Thanks, Dave Seppala

Neither the free pendulum nor the torsion pendulm 'measures'
time but they are both processes dependent on inertial/gravitational
effects. Gravity acts inline with free pendulum's stroke so
it is somewhat like parametric amplifcation (pumping a childs
swing). The length of the pendulum is effectivly shortened at
the extrems of its swing.

Gravity acts orthogonal to a torsion pendulum, so the mass is
effectively following a longer path.

The SUMO space clock was developed to test if a clock with no
oscillating mass would behave differently but its chances of
flying don't look very good.
http://bigben.stanford.edu/sumo/status.htm

Sue...
Sue...
science forum Guru

Joined: 08 May 2005
Posts: 2684

Posted: Sun Jul 16, 2006 12:13 am    Post subject: Re: Clock Properties

David wrote:
 Quote: In Einstein's paper On The Electrodynamics of Moving Bodies he states that pendulum clocks don't behave the same way as other clocks. I don't understand why physicists believe all clocks except pendulum clocks share the same properties in terms of running at different rates in different inertial frames. What property does every other entity have measures time have that pendulum clocks do not and vice versa. Thanks, Dave Seppala

OOps!
My eyeglasses outran my brain. For Special Relativiy you
should refer to the 1920 paper (not the 1905) where you
see the optical path is responsible for any motional
effects.

<< As judged from K, the clock is moving with the
velocity v; as judged from this reference-body, the
time which elapses between two strokes of the clock
is not one second, but... >>
http://www.bartleby.com/173/12.html

....and you'll find the appropriate imaginary operators applied
to the space-time.
http://www.bartleby.com/173/17.html
http://www.aoc.nrao.edu/~smyers/courses/astro12/speedoflight.html

Sue...

http://bigben.stanford.edu/sumo/status.htm
Sorcerer1
science forum Guru

Joined: 09 Jun 2006
Posts: 410

 Posted: Sun Jul 16, 2006 7:38 am    Post subject: Re: Clock Properties "Tom Roberts" wrote in message news:B0fug.121734\$H71.17684@newssvr13.news.prodigy.com... | David wrote: | > In Einstein's paper On The Electrodynamics of Moving Bodies he states | > that pendulum clocks don't behave the same way as other clocks. | | This is PHYSICS, not math or logic, and "proof" is completely irrelevant. Tom Roberts.
guido1
science forum beginner

Joined: 16 Jul 2006
Posts: 1

Posted: Sun Jul 16, 2006 7:46 am    Post subject: Re: Clock Properties

"Tom Roberts" <:
 Quote: In Einstein's paper On The Electrodynamics of Moving Bodies he states that pendulum clocks don't behave the same way as other clocks. This depends on what one means by a "pendulum clock". In common usage, a pendulum clock consists of a box in which a pendulum swings, plus a mechanism to count those swings. Unfortunately, this is not the complete clock -- it depends inherently on the earth's gravitation for its operation, including its tick rate. In freefall such a pendulum clock does not work at all, and on top of a mountain it ticks more slowly than at sea level, and in an airplane its tick rate varies wildly as the plane maneuvers. To be considered as a clock in the sense physicists use the word, one must include the pendulum's relationship with the gravitational source. This makes it impractical to use for most investigations of clock tick rate.

Might we say that there are 'gravitational' clocks, like the pendulum, and
non-gravitational ones? The latter would imply a cyclic motion induced by
non-grav., eg, electromagnetic, forces. Even so, there might be different
families responding to different forces?

 Quote: I don't understand why physicists believe all clocks except pendulum clocks share the same properties in terms of running at different rates in different inertial frames. This is not mere "belief", this is an experimental observation. So only theories that predict such behavior are valid. What property does every other entity have measures time have that pendulum clocks do not and vice versa. All the other clocks that we normally think of (in this context, anyway) are self contained, and their tick rate is not directly dependent on any external quantity; that is NOT true for the pendulum "clock".

Would that imply that gravitation-sensitive aging would differ from, eg,
el.magn. sensitive aging? A body, submitted to all such in relativistic
circumstances, aging differentially in its parts?
And which time SRT or rather GRT tells us about then?
Your paradox twin couldn't tell his age exactly upon return. Would depend on
the clocks consulted...;-)

guido
http://home.scarlet.be/~pin12499/index.html
dseppala@austin.rr.com
science forum Guru Wannabe

Joined: 13 Sep 2005
Posts: 154

Posted: Sun Jul 16, 2006 3:17 pm    Post subject: Re: Clock Properties

On Sat, 15 Jul 2006 23:39:13 GMT, Tom Roberts
<tjroberts137@sbcglobal.net> wrote:

 Quote: David wrote: In Einstein's paper On The Electrodynamics of Moving Bodies he states that pendulum clocks don't behave the same way as other clocks. This depends on what one means by a "pendulum clock". In common usage, a pendulum clock consists of a box in which a pendulum swings, plus a mechanism to count those swings. Unfortunately, this is not the complete clock -- it depends inherently on the earth's gravitation for its operation, including its tick rate. In freefall such a pendulum clock does not work at all, and on top of a mountain it ticks more slowly than at sea level, and in an airplane its tick rate varies wildly as the plane maneuvers. If we exclude all clocks that don't work the same under all conditions

we would eliminate all clocks. Timing mechanisms vary as a function
of temperature, EM disturbances, external pressure, gravitational
effects, etc.
 Quote: To be considered as a clock in the sense physicists use the word, one must include the pendulum's relationship with the gravitational source. This makes it impractical to use for most investigations of clock tick rate. If I have a pendulum clock consisting of a large mass and a pendulum

above this mass, and this clock runs at the same rate as a wind-up
clock and an atomic clock in the same inertial frame, would you
consider that a clock?
And don't pendulum clocks depend on the ratio of masses and length
of the pendulum. If one pendulum clock was oriented perpendicular to
V and an identical clock was oriented parallel to V, where V is the
velocity of an inertial frame relative to the clock, would observers
in the V frame measure that these clocks "tick" at different rates,
while observers in the clock frame measure that these clocks "tick" at
the same rate?
Thanks,
David

 Quote: I don't understand why physicists believe all clocks except pendulum clocks share the same properties in terms of running at different rates in different inertial frames. This is not mere "belief", this is an experimental observation. So only theories that predict such behavior are valid. What property does every other entity have measures time have that pendulum clocks do not and vice versa. All the other clocks that we normally think of (in this context, anyway) are self contained, and their tick rate is not directly dependent on any external quantity; that is NOT true for the pendulum "clock". Tom Roberts
Tom Roberts
science forum Guru

Joined: 24 Mar 2005
Posts: 1399

Posted: Sun Jul 16, 2006 5:45 pm    Post subject: Re: Clock Properties

guido wrote:
 Quote: "Tom Roberts" <: To be considered as a clock in the sense physicists use the word, one must include the pendulum's relationship with the gravitational source. This makes it impractical to use for most investigations of clock tick rate. Might we say that there are 'gravitational' clocks, like the pendulum, and non-gravitational ones?

Sure. There are various techniques for creating clocks. But not all of
them fit easily into such a classification: Consider the clock
consisting of a rotating isolated sphere with a mark on its surface, and
a counter that counts the mark going by. How would this be classified?
Note that the signals received from pulsars (rotating neutron stars) are
essentially like that, and rank among the most accurate time keepers
known (better than most atomic clocks).

 Quote: The latter would imply a cyclic motion induced by non-grav., eg, electromagnetic, forces. Even so, there might be different families responding to different forces?

There might. After all, just about anything is possible.... But actual
measurements of clocks using EM forces (atomic clocks), weak forces
(muon decay), and strong forces (nuclear spin resonance) all behave
similarly for various changes in their environment (e.g. rapidly moving
frames).

 Quote: All the other clocks that we normally think of (in this context, anyway) are self contained, and their tick rate is not directly dependent on any external quantity; that is NOT true for the pendulum "clock". Would that imply that gravitation-sensitive aging would differ from, eg, el.magn. sensitive aging?

We have no way to measure aging via gravitation. All our physiological
functions are electromagnetic. See above for why the type of clock does
not matter.

Tom Roberts
Sue...
science forum Guru

Joined: 08 May 2005
Posts: 2684

Posted: Sun Jul 16, 2006 6:00 pm    Post subject: Re: Clock Properties

Tom Roberts wrote:
 Quote: There might. After all, just about anything is possible.... But actual measurements of clocks using EM forces (atomic clocks), weak forces (muon decay), and strong forces (nuclear spin resonance) all behave similarly for various changes in their environment (e.g. rapidly moving frames).

How can I get a frame to move rapidly through my environment?
I have serveral wheels of cheese I'd like diced and cubed and that
sounds like a spiffy way to do them all at once. )

Sue...

 Quote: Tom Roberts
Tom Roberts
science forum Guru

Joined: 24 Mar 2005
Posts: 1399

Posted: Sun Jul 16, 2006 6:01 pm    Post subject: Re: Clock Properties

David wrote:
 Quote: If we exclude all clocks that don't work the same under all conditions we would eliminate all clocks.

As has been said before: one must not keep one's mind so open that
everything falls out ().

This is why one needs a _theory_ that describes an ideal clock, and then
one evaluates how real clocks compare to the ideal. GR is such a theory,
and it predicts that self-contained clocks all behave the same for
variations is speed and gravitational potential. Real atomic clocks
behave that way to the limits of their intrinsic resolutions, as does
the decay of muons and other elementary particles.

 Quote: Timing mechanisms vary as a function of temperature, EM disturbances, external pressure, gravitational effects, etc.

Sure. But a well-made clock will either control or calibrate those
effects so the user can remove them from the data. Modern atomic clocks
are unaffected by temperature, pressure, and EM fields over ranges
exceeding normal laboratory experience. They can also be calibrated
quite accurately for gravitational effects (i.e. altitude relative to
the geoid) -- this last depends on what the clock is used for: if it is
measuring a proper time then no such correction is used, but if
reference to UTC is required then it is.

 Quote: If I have a pendulum clock consisting of a large mass and a pendulum above this mass, and this clock runs at the same rate as a wind-up clock and an atomic clock in the same inertial frame, would you consider that a clock?

It depends on how accurate one wants it to be. Pendulum clocks are quite
poor compared to modern atomic clocks.

 Quote: And don't pendulum clocks depend on the ratio of masses and length of the pendulum. If one pendulum clock was oriented perpendicular to V and an identical clock was oriented parallel to V, where V is the velocity of an inertial frame relative to the clock, would observers in the V frame measure that these clocks "tick" at different rates, while observers in the clock frame measure that these clocks "tick" at the same rate?

No. Remembering that your pendulum clock includes its own large mass.
The ticking of such a clock consists of the sequence of events for which
its pendulum is at bottom dead center -- each is the intersection of the
pendulum bob with a mark on its enclosure, and that is independent of an
observer's relative velocity or orientation. Of course the usual SR
"time dilation" applies for moving observers, but a real pendulum clock
is unlikely to be accurate enough for that to be measurable.

Tom Roberts
Ben Rudiak-Gould
science forum Guru

Joined: 04 May 2005
Posts: 382

Posted: Sun Jul 16, 2006 6:20 pm    Post subject: Re: Clock Properties

David wrote:
 Quote: In Einstein's paper On The Electrodynamics of Moving Bodies he states that pendulum clocks don't behave the same way as other clocks.

The exact wording from the fourmilab.ch translation is

Thence we conclude that a balance-clock* at the equator must go
more slowly, by a very small amount, than a precisely similar
clock situated at one of the poles under otherwise identical
conditions.

* Not a pendulum-clock, which is physically a system to which
the Earth belongs. This case had to be excluded.

The purpose of the phrase "physically a system to which the Earth belongs"
is to point out the difference between clocks which depend on the Earth's
presence (gravity) for their operation and clocks which don't. The main
result of this section really has nothing to do with the Earth, and the
mention of clocks at different latitudes is just an example. I don't think
that anything actually goes wrong with the experiment if you use a pendulum
clock; I think he excludes such cases just to emphasize that the presence of
the Earth was not considered in the analysis.

-- Ben
The Ghost In The Machine1
science forum Guru

Joined: 25 Mar 2005
Posts: 1551

Posted: Sun Jul 16, 2006 8:00 pm    Post subject: Re: Clock Properties

On Sun, 16 Jul 2006 11:00:23 -0700, Sue... wrote:

 Quote: Tom Roberts wrote: There might. After all, just about anything is possible.... But actual measurements of clocks using EM forces (atomic clocks), weak forces (muon decay), and strong forces (nuclear spin resonance) all behave similarly for various changes in their environment (e.g. rapidly moving frames). How can I get a frame to move rapidly through my environment? I have serveral wheels of cheese I'd like diced and cubed and that sounds like a spiffy way to do them all at once. )

A bullet might make a bit of a mess, but would probably go through a fair
number of gouda wheels. I'm not sure muons are quite as energetic. :-)

 Quote: Sue... Tom Roberts

--
It's still legal to go .sigless.

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