Pendulums

In the middle of Foucault's Pendulum, Umbertro Eco and wondered what the shape of the circle it covers, at the N & S poles, presumably it would describe a perfect circle but what about at the equator? Would the shape still be a circle or would it be an ellipse? Or just a straight line. Can't see it being a straight line, I would think that would only happen if the planet under it was not rotating.

Originally posted by sonhouse
In the middle of Foucault's Pendulum, Umbertro Eco and wondered what the shape of the circle it covers, at the N & S poles, presumably it would describe a perfect circle but what about at the equator? Would the shape still be a circle or would it be an ellipse? Or just a straight line. Can't see it being a straight line, I would think that would only happen if the planet under it was not rotating.

If the pendulum is perfectly along the equator, the Coriolis acceleration would be zero, I think. It sounds weird but it would be a line.

I had to think long and hard about this problem. Actually no I didn't I just looked up the wikipedia page and there are the answers.

http://en.wikipedia.org/wiki/Foucault_pendulum

Originally posted by XanthosNZ
I had to think long and hard about this problem. Actually no I didn't I just looked up the wikipedia page and there are the answers.

http://en.wikipedia.org/wiki/Foucault_pendulum

I didn't understand the effect caused by the fixed stars. Would the pendulum be in a straight line or not?

Boy there is a lot of unsuspected physics in that bob for sure! Unsuspected by me that is. Thanks for the link. I gather the precession at the equator goes to zero, so the pendulum describes the same circle at the equator and at the poles? Interesting about the poleward force. That sounds like all things being equal, the lighter-than-air craft would drift towards the pole and eventually end up there.
So the precession could be used as a way to figure out what latitude you are at by measuring it then backtracking through the equation.

As I see it the answer would be something like this:

If the pendulums first wavelength is a stright line it will still be a straight line in the following wavelength, disregarding the position of the earth.
The same thing happens also if the first wavelength is a perfect circle or a ellips.
It just continues as it is started.

Originally posted by FabianFnas
As I see it the answer would be something like this:

If the pendulums first wavelength is a stright line it will still be a straight line in the following wavelength, disregarding the position of the earth.
The same thing happens also if the first wavelength is a perfect circle or a ellips.
It just continues as it is started.

What are you defining as the 'wavelength'? The size of the circle it proscribes?

Originally posted by sonhouse
What are you defining as the 'wavelength'? The size of the circle it proscribes?

I don't know if it is the correct definition of the term wavelength but here I mean one cycle of movement. Back and forth or a circle (or ellips) around.

Great book, by the way. Much better than DaVinci Code.

Originally posted by narya
Great book, by the way. Much better than DaVinci Code.

Indeed. There are so many referances its like an occult Finnegans Wake. I am about in the middle so have yet to finish it. Am very busy right now, emails to write, music files to send, all not done yet, have to pick up my honda tomorrow, bad transmission shift cable, it seems like an endless list of things to do before I get back to it.