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Foucault pendulum

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Re: Foucault pendulum

#21

Post by pengaru »

NegativeLatency wrote: post #14

Find one near you! https://en.wikipedia.org/wiki/List_of_Foucault_pendulums

I'm surprised to see Fermi National Accelerator Laboratory listed still. When I last visited Wilson Hall which must have been nearly a decade ago now, the pendulum had been removed. If memory serves it happened after the cable snapped from wear and they decided to just get rid of it.

This [0] post claims they removed it in 2010.

It was kind of mesmerizing to watch back in the day, Wilson Hall is a tall building with an open center, it made for a great Foucault Pendulum.

[0] https://www.vofoundation.org/blog/cabinet-physics-riding-alo...

Re: Foucault pendulum

#22

Post by gregfjohnson »

lurquer wrote: post #11

I found it very difficult to understand WHY Foucaults pendulum behaves the way it does. I could picture what was happening with the pendulum at the Norh Pole... earth rotates under the pivot point every 24 hours. And, I understand what happened st the Equator... no effect on the pendulum as nothing is rotating beneath it. But, at points in between, it was hard to understand why the pendulum might only rotate 80% or s…

Here's the intuition that clicked for me, similar to the above but with a different twist at the end.

Imagine a large flat parking lot, and drive around the parking lot in a circle. Say you have a small pendulum swinging freely, suspended in your car. If you drive the full 360 degrees, the pendulum will appear from the reference frame of the inside of the car to have rotated a full 360 degrees. (Let's say that you are driving fast enough to render the rotation of the earth, the latitude of the parking lot, etc. negligible.)

Whatever fraction of the circle you drive, the pendulum will appear to rotate that same fraction as viewed from inside the car.

Now, here is the fun part. Imagine that you are driving at some fixed latitude on a large sphere. Create a big cone that is just tangent to the sphere on your path. What happens if you drive the entire distance and return to your starting point?

Cut the cone in a vertical straight line starting at its apex, and then flatten out the cone. It will form a flat circle, but with a pie slice removed.

If you had driven the perimeter of this partial circle in the parking lot, you would see that the pendulum only rotated part-way around. The same thing will happen if you drive the full distance around the sphere at the corresponding latitude.

Re: Foucault pendulum

#23

Post by sandworm101 »

The Foucault Pendulum is on my list of three dead-simple machines that prove science is real.

(1) Using a soup can and some string to measure radiation: https://en.wikipedia.org/wiki/Kearny_fallout_meter

(2) Measuring the force of gravity, and thereby weighing the earth, using a tuna can and some other string. http://www.fourmilab.ch/gravitation/foobar/

(3) Using a string and a bowling ball prove the earth is round without going outside. https://en.wikipedia.org/wiki/Foucault_pendulum

Re: Foucault pendulum

#24

Post by redis_mlc »

aidenn0 wrote: post #12

TIL the smithsonian removed it's Foucault pendulum in 1998 (right about when I moved away from the DC area). It was about 15 meters long and quite impressive; they had little pins setup that it would knock down, so you could look at when you arrived in the museum and see the difference when you left.

The Oregon Convention Center has one, watched it every O'Reilly Open Source Conference that was in Portland.

https://www.youtube.com/watch?v=-p7P0DQvp0g

Re: Foucault pendulum

#26

Post by erikig »

sandworm101 wrote: post #23

The Foucault Pendulum is on my list of three dead-simple machines that prove science is real. (1) Using a soup can and some string to measure radiation: https://en.wikipedia.org/wiki/Kearny_fallout_meter (2) Measuring the force of gravity, and thereby weighing the earth, using a tuna can and some other string. http://www.fourmilab.ch/gravitation/foobar/ (3) Using a string and a bowling ball prove the earth is round w…

I didn't know about Cresson_Kearny [1] until this but he was pretty great. He reminds me of a cold war Macgyver-like survivalist with a number of interesting gadgets [2]

[1] https://en.wikipedia.org/wiki/Cresson_Kearny

[2] https://en.wikipedia.org/wiki/Kearny_air_pump

Re: Foucault pendulum

#28

Post by mdturnerphys »

The one at BYU has signs around it saying something like "Warning! 10,000 ohms! Do not touch!" I guess the thinking is that those who don't know what ohms are will think it's dangerous and those that do will have enough respect for physics to not disturb the pendulum.

Re: Foucault pendulum

#29

Post by saagarjha »

aidenn0 wrote: post #12

TIL the smithsonian removed it's Foucault pendulum in 1998 (right about when I moved away from the DC area). It was about 15 meters long and quite impressive; they had little pins setup that it would knock down, so you could look at when you arrived in the museum and see the difference when you left.

If you’re ever in the Bay, the California Academy of Sciences has one (although it’s probably one of the more boring exhibits there).

Re: Foucault pendulum

#30

Post by redis_mlc »

lidHanteyk wrote: post #5
empath75 wrote: post #2

> The pendulum was introduced in 1851 and was the first experiment to give simple, direct evidence of the earth's rotation. The existence of the day-night cycle should have sufficed.

In addition to sibling comments, we should note that not all observations are experiments. There is a distinct difference between experiment and mere observation: In an experiment, we are carrying out a repeatable recipe in order to try to falsify a hypothesis. We are not merely theory-crafting, working to explain what we see, but we are trying to disprove what we have theorized.

> In an experiment, we are carrying out a repeatable recipe in order to try to falsify a hypothesis. We are not merely theory-crafting, working to explain what we see, but we are trying to disprove what we have theorized.

Actually, no. Not sure where you got the idea that an experiment has to falsify a hypothesis.

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