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How To Build a Short Foucault Pendulum
KentuckyFC writes "Set a pendulum in motion and you'll inevitably give it an ellipsoidal motion, which naturally tends to precess. That's bad news if you want to build a Foucault Pendulum, a bob attached to a long wire swinging in a vertical plane that appears to rotate as the Earth spins beneath it. The natural precession always tends to swamp the rotation due to the Earth's motion. There is a solution, however: the behavior of the ellipsoidal motion is inversely proportional to the pendulum's length. So the traditional answer has been to use a very long pendulum (Foucalt's original in Paris is 67 meters long). Now scientists at Carnegie Mellon University have another solution (abstract). They've created a motor that drives a pendulum in a way that always cancels out the precession. That means the effect of Earth's rotation can be seen on much shorter pendulums such as the 3-meter pendulum on which they've tested their motor. That's just the start though. They say there is no limit to how short the new generation of Foucault Pendulums can be, and even talk about the possibility of tabletop devices."
A new generation of executive ball-clickers is born.
Swingin' baby!
"Life is not magic." Dr. Ron Weiss - "If we don't play God, who will?" Dr. James Watson
Next useless item available for purchase on Think Geek?
You insensitive clod.. I'm off-world on a non-rotating frame of reference... my pendulums don't precess in ellipsoidal motion, you dirty-minded person, you.
That sounds like a feat of engineering, not science.
At any rate, I'm sure the pendulum clock industry is ecstatic. Can I get a Ph.D. for building a motor to flip sand-filled hourglasses over?
A slashdotter who didn't build his own computer is like a Jedi who didn't build his own lightsaber.
(maybe slightly OT)
As well as a physics experiment, Foucault's Pendulum is a fantastic book by Umberto Eco.
It's in the same subject area as the Da Vinci Code before that opportunist lightweight Dan Brown ever put pen to paper, and it has far more depth and erudition. There's even some code (BASIC) in it...
What if I pull the pendulum using a string, tie the string to a fixed object, wait for the pendulum to stop moving, then cut the string?
Or any of a hundred other methods; that's just the first that came to mind.
I'd be more concerned about vibrations, friction effects, poor suspension system, etc. that affect the precession of a small pendulum after it starts swinging. Fortunately this device seems to counteract those forces as well.
How can I believe you when you tell me what I don't want to hear?
When I was a kid I used to dream about having a tabletop Foucalt pendulum. My friends told me I was mad, and my parents tried to discourage me from thinking about it. "There's no such thing as a small Foucalt pendulum, Zouden! Maybe one day we'll take you to visit the one in Paris, but you'll never get to have your own one." Now, finally, my prayers have been answered.
"A week in the lab saves an hour in the library"
Foucault. Not 'Foucalt'.
Foucault. With a 'u' between the 'a' and the 'l'.
Please correct the summary. It is a Foucault pendulum not Foucalt.
Take one banker, tie rope to neck, swing. Prod occassionally.
I want a list of atrocities done in your name - Recoil
I live near the equator, you insensitive clods!
How do we know the motor isn't causing the precession?
That's the most stupid thing I read in the last time... why do you need a FC in the first place if you put a motor into it...
It's like... showing that birds can fly by stuffing them into a cannon and fireing them upwards....
... Sharper Image went out of business.
However, there is a huge market for "executive ball-busters".
Give a man a fish and you have fed him for today. Teach a man to fish, and he'll say "WHERE'S MY FISH, YOU IDIOT?"
Doesn't using a motor to modify the swinging of the pendulum defeat the whole purpose? I thought the point was to have it seem like it was magically rotating...having a motor modify the swing, takes away from that magic.
sig? uhh, umm, ok
SMAH used to have a Foucalt Pendulum in their main entrance lobby right in front of the original Star Spangled Banner. Damn if that wasn't one of my favorite things in Washington. Sadly, it was removed after being modded -1 off topic.
Short Foucault Pendulum with a length below 3 meters are nothing special, e.g. physics department in Wuppertal. 3 cm would be special. Btw, very long pendulums have problems on there own as well -- like standing waves on the pendulum.
Is there really a lot of demand for a table-top device that measures the rotational velocity of earth? Wouldn't it be easier to just google it?
I've abandoned my search for truth; now I'm just looking for some useful delusions.
... anyone?
When my school wanted to build a Foucault pendulum that was less than 1 story high to decorate a new building, they installed a gadget at the top that automatically dampens the precession. This was over ten years ago.
Absolutely the only reason for going when I was young. Otherwise, meet me in the air an space museum.
Is it just my observation, or are there way too many stupid people in the world?
People said i was daft to build a short Foucault pendulum. but i built it anyway... it started to precess .. so i built another one. that started to precess. so i built a third one. That one started to precess then fell over and burst into flames. but the FOURTH one worked great. and that's what your getting my lad the shortest Foucault pendulum in the world!
This is very cute. The pendulum is powered, weakly, by a coil centered under the pendulum's rest point pushing against a permanent magnet in the bob. This is symmetrical; it pushes radially away from the rest position. So there's no active control over the direction of swing.
The new insight is that if the pushing pulse is delayed to the right point in the cycle, the applied force dampens, rather than increases, the tendency for the oscillation to become ellipical. The optimal time for the pushing pulse has been worked out. It's a neat little result.
Of course there is a far simpler solution to demonstrate the same effect: build a large turntable and put your short pendulum on that. Since the rotation is far faster than the Earth's the short pendulum will show precession when you sit on the turntable and stays stationary as the table turns if you are not on it.
The big advantage to this approach is that you can put a video camera into both frames which really shows the difference. I've got a couple of videos of this which I made for my lectures which I should probably to upload to YouTube.
But when the Templi Resurgentes Equites Synarchici start kidnapping Carnegie-Mellon's staff to use in an occult ritual, don't say you weren't warned!
Choose another unit.
Good judgement comes from experience, and experience comes from bad judgement.
- W. Wriston, former Citibank CEO
That it isn't the size of your *pendulum* that matters, It's the motion.
So maybe it will be possible to locate the island with a home setup instead of going to that creepy church. :)
...been doing this furlong.
Rampant carbon sequestration destroyed the Dinosaurs' tropical paradise. I'm here to help repair the damage.