
'Temperamental' Big Ben was ringing up to six seconds late - bootload
http://www.bbc.com/news/uk-england-london-34051053
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tobylane
It's had all sorts of challenges over time. The Circle and District are just
under the surface nearby, the Jubilee line is deep but still affected the
foundations. The building across the road was demolished down to about six
levels below ground level. The buildings it is attached (including Parliament
and a school) to are up to 1000 years old and need to be vacated for major
works from every type of damage, including WWII bombings. Also it's on the
edge of what was once an island, and there's an underwater river nearby.

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m0nty
> The clock is altered by adding and removing old coins from its pendulum to
> change the rate at which it swings.

British engineering at its finest. I understand they have a stock of
discontinued six-pences and ha'pennies which weigh only a few grammes each and
are used for these fine adjustments.

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rurounijones
Do they literally have to put these and take them of as the thing is swinging
back and forth?

I am also thinking of unfortunate scenario where someone adds /removes
momentum accidentally while trying to place pennies.

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CiaranMcNulty
I don't believe a pendulum's period is affected by its momentum at any point
in its arc, just the length and its mass.

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joe5150
Just the length, rather. The mass has no effect on the period.

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richmarr
For a frictionless pendulum in a vacuum this is certainly true.

The article repeatedly says they add weights to the pendulum though, which
makes me wonder whether either (a) it's some connected mechanism they add
weights to, or (b) this is somewhere reality diverges from the simple model.

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rtkwe
[https://youtu.be/5qEPDXDVxvw?t=169](https://youtu.be/5qEPDXDVxvw?t=169)

They're added directly to the 'pendulum shelf' which looks like it's right at
the top of the pendulum. That would adjust the length up (shorter) by a tiny
amount by shifting the center of mass of the pendulum up. This squares with
the simple model of a pendulum.

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sdoering
Damn it. Knowing how hard it can be to tune a mechanical wrist watch to be
within some seconds of atom time in 24 hours, this kind of precision on a
clockwork that big is really amazing.

Would never have thought that. I am totally impressed.

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BobLaw
Definitely a neat fix for something that worked for 150+ years and only needed
to be checked a couple times a week.

Now that it has to be manually checked at least once a day though ... I don't
know. Seems like a lot of trouble for something that could be solved with an
Arduino and a water pump.

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drzaiusapelord
>Mechanics discovered it became delayed over the weekend of 15 and 16 August
but have now gradually fixed it.

I would love to automate this with a nagios-like alert system and perhaps a
robot arm to add/remove coins.

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nateguchi
I guess the BBC would notice this pretty fast - they have a microphone live
broadcasting the bells for the beginning of the radio news

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iaskwhy
From the article: "The incorrect chimes had caused interruptions to BBC Radio
4, which broadcasts the sound of Big Ben live."

