Foucalt's Pendulum

Just visited Franklin Institute and you can see one in action there:

Cool stuff.

That is on my list of things to do.

to see Foucalt's Pendulum at the Chicago's Museum of Science and Industry,

I took a 4 day vacation to Chicago last summer, did not have enough time.

I was there last spring! If you go make sure you plan it as at least a two day trip.

Three if you walk slow or have a wife who gets lost easy.

Its a huge place!

Thanks,

Last year I stayed at Grant Park, Walking distance to Shedds Aquarium and Earth History Museum.... and Bubba Gump's Shrimp by the Navy Pier, as well as the stuff going on at or near the park. All within (3) miles good walking distance. I thought 4 days was enough for this, and it was......... but not a minute was wasted, yet it was very relaxing.

Next time, I thought it would be this summer, but hey hopefully this fall, I also want to get in the time to visit the WWII German U-Boat. but first..... I have to get the time..... I have 150 hours of PTO (Paid Time Off) to use........ but we are in the mist of an expansion........

^{My end, I should have been wrapped up last week, but refining the process, I see two weeks left.}

Good to know all this. I've been thinking about a trip to Chicago to do a Frank Lloyd Wright tour. I'll have to add this stuff to my plans.

When I was a kid I saw a Foucault Pendulum at the Buhl Science Museum in Pittsburgh. Thought it was cool. Neat planetarium show too. Not sure any of that is still there though.

Oh, that's right, I went to the planetarium there also.........right next to shedds. They have some professors from the University of Chicago there for open discussion......

There is a Foucault's Pendulum installation in the Science Museum, in South Kensington, London.

I had a discussion with my dad on how they keep it running without affecting the swing in any way. My best guess is that they lift it on the upward stroke and drop it on the downward so that the downward has just a little bit more energy to make up for losses in each swing.

I really want to build one someday : )

Drew K

I thought it was just the momentum. any induced energy may effect the swing. could be wrong.

They use an electromagnet system to give the pendulum a little kick along its stroke to replace the energy lost with each swing.

I am pretty sure that mechanism is near the top of the pendulum's top of the cable, so you never see it, but it is there.

I thought about that, but it would be difficult to do that without affecting the direction of travel. The most simple solution would be to change the period of the pendulum slightly so that the path upward was just a little shorter than the path downward.

Drew K

From the Smithsonian website, a bit more info to add to AH's comments:

"...To do this, two iron collars are attached to the cable near the top. There is a doughnut-shaped electromagnet built into the ceiling, and the iron collar swings back and forth inside the hole of the doughnut. When the pendulum cable reaches a particular point in its swing, it is detected by an electronic device and the magnet is turned on at just the right time to give the collar (and thus the cable and the bob) a little "kick" in the exact direction of its natural swing. This restores the energy lost during the swing and keeps the pendulum from stopping. It has no effect on the direction of the swing, and thus does not interfere with the demonstration that the earth is rotating...

Well, I guess that could work too...I just thought it would be a mroe elegant solution to change the period slightly. I wonder if they are all powered like that?

Drew K

The wikipedia page says they're sometimes manually reset, possibly using a flame to burn through a thread holding the bob so the motion begins cleanly.

The first time I saw one of these, the thought occurred to me... Would it be possible, at least in principle, to remove energy from the earth's rotation, say with a large frictionless gyroscope?

I've given this more thought and I believe the conservation of angular momentum would keep it from working. I suspect that if you had a giant gyroscope and forced it to do work to stay aligned in a fixed direction, any energy you received would come from the rotational energy of the gyroscope.

It actually can be done, not with a gyroscope, but with a tidal power station. This increases the earth's drag on the moon, causing the earth to slow down and the moon to move to a higher orbit. The angular momentum is transferred from the earth to the moon. The moon gains some energy, the earth loses more, and the difference in energy is extracted by the power station.

A bit off the subject, but I know when I went to Penn State there was one in Deike Building. (42 years ago) That building had a large tower and was the only place one could be placed. It appears to be gone now, as it doesn't make Wiki's list of installations in Pennsylvania.

Any Nittany Lions out there know where it went?