2201: Foucault Pendulum

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Foucault Pendulum
Trust me, you don't want to get on the wrong side of the paramilitary enforcement arm of the International Earth Rotation and Reference Systems Service.
Title text: Trust me, you don't want to get on the wrong side of the paramilitary enforcement arm of the International Earth Rotation and Reference Systems Service.


Ambox notice.png This explanation may be incomplete or incorrect: Created by the International Earth Rotation and Reference Systems Service. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.
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Black Hat is attending what appears to be a physics lecture. The professor, Megan, is talking about the Foucault pendulum, a device which demonstrates the rotation of the Earth. Black Hat, being himself, sees an opportunity to cause chaos and seizes it with both hands, quite literally - that is, he grabs the pendulum. The professor objects strongly to this, seemingly for fear of ruining the delicate demonstration. However, the news anchor in the final panel reveals to us that by arresting the motion of the pendulum, Black Hat has somehow stopped the rotation of the Earth. This of course is blatantly impossible since the Foucault pendulum's motion is tied to the earth's rotation, not the other way around. [citation needed]

A Foucault pendulum swings from a bearing that allows rotation in any direction, like your shoulder joint instead of your elbow. If the Earth were stationary, it would continue to swing in the same plane as when it was released. However, because the Earth moves beneath it, over the course of the day the pendulum's motion gradually changes direction relative to the room. The low-resistance bearing doesn't allow the rotation of the Earth to affect the motion of the pendulum, so it stays aligned to its original inertial reference frame rather than the rotating one of the Earth.

The fact that the Earth's rotation does not influence the motion of the pendulum does NOT mean that other things can't affect it - for example, by running up and manually repositioning the pendulum. Of course, the apparent rotation of the pendulum's plane relative to the Earth is an effect of the planet's motion, rather than the cause of it. Thus, stopping a Foucault pendulum manually does not entail pausing the rotation of the Earth.

If it were somehow possible for a Foucault pendulum to control Earth's rotation, Black Hat would probably not want to alter the momentum of the pendulum, unlike most cases where he causes chaos (assuming he was told that it was related to Earth's rotation and assuming that he would prefer to preserve his own life over making chaos). The reason why is because if the rotation of Earth were to be stopped for even very short amounts of time (a few seconds), it would cause everything on Earth that wasn't bolted/fastened to the ground to be sent flying eastward (assuming they are near the Equator) at a speed of 300-360 meters per second, likely causing the death of most lifeforms on Earth within an hour or less, and causing massive windstorms and weather events on a scale not previously observed on Earth. This would likely cause a mass extinction event and wipe out ~90% of humanity. It is possible that Black Hat's grabbing the pendulum would cause a gradual slowing prior to stopping, minimizing the issue, but the results would still be catastrophic.

Randall covered this scenario in detail in his What If book.

The title text refers to a (probably) fictional paramilitary enforcement arm of the International Earth Rotation and Reference Systems Service and the foolishness of tangling with such a force. If Foucault pendulums were somehow able to influence the rotation of the Earth in any measurable way, the IERS enforcers would probably strictly control their installation and monitor their use (and misuse). Black Hat is likely in for a rough day.


The Foucault Pendulum in this comic strongly resembles that in the Museum of Science in Boston (both in shape and the way it is knocking over the pegs)


Ambox notice.png This transcript is incomplete. Please help editing it! Thanks.

[Cueball, Black Hat, Ponytail, and Megan are standing next to a large swinging sphere on a pendulum with markers under it; Megan is pointing at it.]

Megan: This Foucault pendulum demonstrates Earth's rotation. It stays in a fixed plane while the Earth rotates under it.

[Close-up on Black Hat]

Black Hat: Hmm, really. So that means...

[Close-up on Black Hat and pendulum; Black Hat grabs pendulum, and a line points from the pendulum saying "GRAB!"]

Character out of panel: Hey!

Character out of panel: Stop him!

[Blondie is standing next to Black Hat's picture in an inset frame, captioned with "BREAKING NEWS."]

News Anchor: The Earth's rotation was briefly halted today until geophysicists wrestled the intruder to the ground...

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Why are we assuming there are any side effects like these? The pendulum stops the Earth from rotating -- couldn't this include the entire planet, including the atmosphere and loose objects such as humans? There probably would be some volcanoes from the sudden loss of centrifugal force, though. 13:52, 13 September 2019 (UTC)

I take it the pendulum is somewhere deep underground, which would shield Black Hat from the cataclysmic side effects? Besides, they have several backup pendulums that while not enough to maintain rotation are sufficient to slow the half enough to preserve life. 20:11, 11 September 2019 (UTC)

I fear that the use of multiple pendulums to smooth out the catastrophy of stoping the Earth's rotation would probably just cause bits of the Earth to keep going and other bits to stop. Hey! That's plate techtonics! Obviously there are subtly dampened/purturbed pendula in secret (masonic?) temples all across the world, making all that happen! Someone likely pushed the one in Atlantis too far, one fateful day...
(BTW, the unsaid catastrophe element reminds me of a classic short story) 15:29, 12 September 2019 (UTC)
These effects will of course not work on Black Hat or any other that are at the Eart Rotation controlling Pendulum at The South Pole observatory. There the Earth stopping will not have any effect :-) --Kynde (talk) 10:53, 13 September 2019 (UTC)
Well, maybe a bit of nanodiziness..? 16:17, 16 September 2019 (UTC)

If the pendulum could really affect Earth's rotation, Black Hat wouldn't need to stop the pendulum entirely; he'd only need to prevent its plane of oscillation from rotating. Another thought: if the pendulum and Earth's rotation were really bidirectionally linked somehow, there would probably be nothing Black Hat could do to alter the pendulum's plane of oscillation -- any more than he could alter the rotation of the Earth with just one human being's strength. That last thought doesn't seem to be the case within this story, though, or else the final frame's news report wouldn't have happened. Trueflint (talk) 20:46, 11 September 2019 (UTC)

Who says it's the energy from Black Hat's grab specifically? Maybe the magic pendulum just tells a device in the Earth whether or not the planet should be spinning, based on the current state of the pendulum. 08:15, 12 September 2019 (UTC)

Why does the description description Megan as a "professor?" She could just as easily be a teacher, a docent, a scientifically-interested parent, or just a random bystander. 11 September 2019

Agree this is more like a tour guide if anything. I will correct this. --Kynde (talk) 10:51, 13 September 2019 (UTC)

The sentence "It stays in a fixed plane while the Earth rotates under it." and the correspoding text in explanation are wrong. It would be true only if the pendulum was located on one of Earth's poles. Elsewhere, the plane in which the pendulum moves would still rotate with respect to its surrondings, but slower than on the pole. The rotation speed is proportional to the sine of latitude. At the equator, the plane would stay fixed with respect to its surroundings. See Wikipedia.-- 23:45, 11 September 2019 (UTC)

As a Physics teacher, I strongly support this. The fact that a Foucault's pendulum is keeping its oscillation plane constant with respect to an absolute reference frame is a common misconception, it should be mentionned as frequently as possible.-- 09:17, 12 September 2019 (UTC)
The reason this pendulum works on Earth rotation is of course that it is the one placed on the South pole! That must be obvious (apart from this being a silly, though very funny, comic). :-D --Kynde (talk) 10:51, 13 September 2019 (UTC)

The Foucault Pendulum in this comic strongly resembles the one in the Franklin Institute in Philadelphia (both in shape and the way it is knocking over the pegs). Perhaps this should also be noted in the trivia section? 05:16, 12 September 2019 (UTC)

Then list *all* the ones it strongly resembles. Do you think Philadelphia’s is the only one with pegs? I think that is the usual presentation. 10:01, 12 September 2019 (UTC)
A Google search reveals that nearly all of them have a weight that looks like the one in this comic, and many of them have some sort of pegs to demonstrate the circular motion over the course of a day. To put the location of any of them in the explanation (as it is now) is probably not appropriate. If there is a significant one somewhere in the world (largest, oldest, etc), then maybe we could mention that specific one. Ianrbibtitlht (talk) 14:56, 12 September 2019 (UTC)
But this is the one that determines the Earth Rotation (and is placed at a pole, see above ;-) Also the one in a small museum here in Aarhus Denmark has the same setup --Kynde (talk) 10:51, 13 September 2019 (UTC)

Do we have anything about resonance transfer being proportional to the difference in mass? 16:20, 12 September 2019 (UTC)

I don't think there's any indication that this comic takes place during a physics lecture. It's more likely that it takes place in a science museum, and this is a museum tour guide explaining the Foucault Pendulum to museum visitors. Ianrbibtitlht (talk) 00:16, 13 September 2019 (UTC)

Agree and will change this now. --Kynde (talk) 10:51, 13 September 2019 (UTC)

I don't know if it's still the case, but back in the 90s some Earth orientation work was very hush-hush military business. It turns out that really detailed models of how the Earth moves are important for targeting long-range missiles. Dfeuer (talk) 02:35, 13 September 2019 (UTC)

Are you suggesting that has some relevance to this comic about the Foucault Pendulum? Ianrbibtitlht (talk) 03:07, 13 September 2019 (UTC)
I'm suggesting it could relate to the notion of paramilitary forces coming for someone who's messing around with Earth orientation. Dfeuer (talk) 12:50, 13 September 2019 (UTC)

You really do not want to mess with IERRSS (IRS for short). Also, the pendulum is in an inertial reference frame to what? Can it be used to detect earths rotation around the sun as well, and the solar systems rotation around the galactic core Torax (talk) 10:16, 13 September 2019 (UTC)

This is one of my new favorites. Love this idea, and of course Black Hat's reaction to the possibility for mayhem.  :-) --Kynde (talk) 10:51, 13 September 2019 (UTC)

Someone should register ierrss.org...

IERS.org is already taken. They are headquartered in Germany and their email is central underscore bureau at iers dot org. You do not want to mess with their paramilitary enforcement arm, because it doesn't want to mess with you. There is no general algorithm for harmonic resonance leveraged momentum transfer. 17:25, 13 September 2019 (UTC)