Stupid Question About Foucault Pendulum

[andyfox]

Isn't the ceiling from which the pendulum is suspended rotating with the earth? Then why would the pendulum itself not rotate in unison and thus not appear to change direction?

Thanks.

[Lestat]

Stupid answer?

Maybe the thing it is suspended from is attached to the ceiling by something that swivels?

I'm not being sarcastic. I really don't know, I just like guessing.

[hmkpoker]

My uneducated guess would be because there is no acceleration taking place.

[thylacine]

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Isn't the ceiling from which the pendulum is suspended rotating with the earth? Then why would the pendulum itself not rotate in unison and thus not appear to change direction?
Thanks.

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Twisting the suspending string or wire at one end doesn't have much effect on the other end, or at least you would want to make it this way.

[Sephus]

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My uneducated guess would be because there is no acceleration taking place.

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i'm pretty sure everything on earth is accelerating all the time. maybe i just nitted you, i dunno.

[yukoncpa]

You are correct if the pendulum is at the equator.

At either the North Pole or South Pole, the plane of oscillation of a pendulum remains pointing in the same direction with respect to the fixed stars, while the Earth rotates underneath it, taking one sidereal day to complete a rotation. When a Foucault pendulum is suspended somewhere on the equator, then the plane of oscillation of the Foucault pendulum is at all times co-rotating with the rotation of the Earth. What happens at other latitudes is an intermediate between these two effect.

from wiki (http://en.wikipedia.org/wiki/Foucault_pendulum)

[hmkpoker]

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My uneducated guess would be because there is no acceleration taking place.

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i'm pretty sure everything on earth is accelerating all the time. maybe i just nitted you, i dunno.

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Huh? My point was that the earth's rotational speed is constant (or close enough). Hang the pendulum in a bus that's accelerating and it will fall back with the bus's speed. Once the bus comes to a constant cruising speed, the pendulum will function normally.

[Sephus]

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My uneducated guess would be because there is no acceleration taking place.

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i'm pretty sure everything on earth is accelerating all the time. maybe i just nitted you, i dunno.

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Huh? My point was that the earth's rotational speed is constant (or close enough). Hang the pendulum in a bus that's accelerating and it will fall back with the bus's speed. Once the bus comes to a constant cruising speed, the pendulum will function normally.

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like i said, maybe i'm just being nitty about your word choice. even if the earth rotates at a constant speed and an object on the surface travels at a constant speed the object is still accelerating toward a point on the earth's axis (if that even makes sense). maybe i'm making an ass out of myself but i just meant there's always "acceleration taking place."

[yukoncpa]

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there's always "acceleration taking place."



[/ QUOTE ] yeah, if I recall from basic physics, any time something is traveling along a curve ( as opposed to a straight line ) even if it's traveling at a uniform velocity, it is accelerating.

[Sephus]

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there's always "acceleration taking place."



[/ QUOTE ] yeah, if I recall from basic physics, any time something is traveling along a curve ( as opposed to a straight line ) even if it's traveling at a uniform speed, it is accelerating.

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FYP. i'm like the high school physics nit in this thread.

[andyfox]

I read the wiki article. What I don't get is "when the earth rotates underneath it." How is the earth rotating underneath it when the pendulum is attached to the ceiling which is also attached to the earth. Won't the ceiling be rotating just as the aerth is? Or is some kind of motor attached to the pendulum that keeps it from rotating in sync with the earth?

[yukoncpa]

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I read the wiki article. What I don't get is "when the earth rotates underneath it." How is the earth rotating underneath it when the pendulum is attached to the ceiling which is also attached to the earth. Won't the ceiling be rotating just as the aerth is? Or is some kind of motor attached to the pendulum that keeps it from rotating in sync with the earth?

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If it were a regular, rigid pendulum, like that in a grandfather clock, the whole apparatus would rotate right along with the earth. But a Foucault pendulum is a piece of string with a weight on the end. If you were to stick this weighted string in a Grandfather clock and set the weighted string swinging, then manually rotate, or twist, the grandfather clock, the weight at the end of the string would soon smash through the clocks glass.
This is at least the way I envisioned the whole thing working when I saw a Foucault Pendulum. I hope I’m not too far off base.

edit - Oh, I just thought of a better example. If a man is swinging at the end of a rope and you were to twist the gallows around, the swinging man would still swing in his same, original direction. It’s just the wooden gallows that are rotating.

[Borodog]

Andy,

Foucalt Pendulums are usually built with a freely swivelling pivot.

[carlo]

This may be germane but I'll let the physicists respond. Once learned of what is know as the Coriolis(spelling) Force which is taken into account due to the spin of the earth. In particular inrocketing into outer space or to another part of the planet this rotational force has to be considered or we get the big miss.

Amazing how a small effect at take off can throw one off by hundreds(thousands?) of miles if for example shooting a rocket from Florida to the Black Sea.Had this question on a test once and definitely missed and caused WW3.