OT: Physics

[Alfred Zweistein]

Alfred's turning in his grave.

[The Natural Philosopher]

We were actually discussing gravity as a macro, not relativistic effects.

[Syd Rumpo]

Cheers

[Huge]

Wriggles well, doesn't he?

[dennis]

That would be caused by the different speeds it would be travelling at the top of the block and the bottom of the block and where it was on the planet then.

[Cursitor Doom]

One of the very best out there. ;->

[Albert Zweistein]

Would it? In the case of the higher g clock maybe the increased pendulum acceleration on the way down would be matched by the increased deceleration on the way up so that the period would be the same at the top and bottom of the block. Maybe one of the propeller heads in here could work out if that's true or not.

[Tim+]

I believe that you are correct. Changing the weight of a pendulum has no effect, it's the length that determines the frequency (theoretically at least)

Having said that I believe that the clock in Big Ben is fine tuned by adding old pennies but this might be working by minutely changing its centre of gravity up or down rather than being due to the weight per se.

Tim

[Albert Zweistein]

Scrub that it's bollocks, my brain was still in plumbing mode.

[Albert Zweistein]

Yes I neglected to mention that the momentum of the faster moving pendulum would carry it higher as it were so it's this that gives unequal masses suspended on the same length the same period as the pendulum in the higher gravity well travels further but moves faster each swing. Which is what you said boils down to.

Hmm could be, variable air pressure comes into the equation as well of course. Does anyone make a pendulum clock that operates in a vacuum?

[Martin Bonner]

No he isn't (as he promptly commented). Changing the mass of the pendulum has no effect (the extra force is exactly balanced by the extra inertia it has to overcome), but changing the gravity field in which the pendulum is operating *will* change the frequency. (Higher gravity -> higher force pulling the pendulum down -> higher speed at the bottom -> higher frequency. I can't remember if there's a root in there or not; probably not.)

Correct.

[Albert Zweistein]

Indeed there is. T = 2??(L/g) I used to know this stuff without googling but that was many years/brain cells ago.

[dr.s.lartius]

It it well-known but much-forgotten that, for a pendulum, T = 2?? ??(L/g) ; therefore, a pendulum clock runs slower when it is higher up. That is Newtonian physics.

Since acceleration and gravity have similar effects, a pendulum clock will run faster if the top is tied to a piece of cord and whirled in a horizonta l plane about the whirler. Orientation can be determined by letting go of the string, after which the clock will undoubtedly go west (younger readers may not understand that).

Non-pendulum clocks (except when radio-controlled) show a small general-rel ativistic effect as the gravity potential changes - I forget the direction

- which can be detected with the aid of the Mössbauer Effect and the P ound?Rebka experiment.

[Syd Rumpo]

Which is an approximation and accurate only at small amplitudes.

Cheers

[Martin Bonner]

Yes. But it *is* the dominant term even at large amplitudes. Do the other terms have 1/?g or not do you know? (Obviously the air-resis tance and friction terms won't).

[Big Les Wade]

I would think so, since the exact equation (neglecting resistance) is

a'' + sin a = 0

where the time-variable is in units of sqrt(r/g).

[Syd Rumpo]

Wikipedia has a good article on the subject. Two pie root ell over jee is there, but multiplied by a whole load of small twiddly bits.

Cheers

[pamela]

:-)

[ed]

On Wednesday, November 25, 2015 at 11:05:49 AM UTC, [e-mail] wro te:

?(L/g) ; therefore, a pendulum clock runs slower when it is higher up. That is Newtonian physics.

l run faster if the top is tied to a piece of cord and whirled in a horizon tal plane about the whirler. Orientation can be determined by letting go o f the string, after which the clock will undoubtedly go west (younger reade rs may not understand that).

elativistic effect as the gravity potential changes - I forget the directio n - which can be detected with the aid of the Mössbauer Effect and the Pound?Rebka experiment.

The difference of the rate of a pendulum clock at the equator from one in a polar location is about 0.25%. This is due to gravity being stronger at th e poles. This would amount to about 200s per day.

Relativistic effects are much much weaker but would make equatorial clocks run faster.

[ed]

True but the error is quadratic and very small at small amplitudes. Pendulu m clocks also keep the amplitude nearly constant.