Author Topic: Anyone familiar with this 'claim' at Aulis.com?  (Read 47010 times)

Offline theteacher

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #105 on: February 22, 2013, 09:28:10 PM »
It's amazing how many things in the sciences, whether biology or physics or other, are counterintuitive.

I can give you a great example of this, from my Form 2 (9th grade in USA) Science class.

The Physics Teacher set up an experiment using a small rectangular flat sheet of aluminium attached along the middle of the short side to a pivot point. The pivot point was designed so that the sheet could only swing edgewise like a pendulum (i.e., it was unable to spin or rotate flatwise)

He then lifted it up to horizontal and let it go. Of course, the sheet swung freely back and forth numerous times, only slowing down through friction at the pivot point and I guess a small amount of air resistance.

Then, he stopped the sheet, and positioned a powerful "C" shaped magnet (one of those that has the poles about an inch apart and facing each other) so that the aluminium sheet would swing between the poles. He asked us what we expected to happen, and without exception we all said that it would just swing on through because we all knew aluminium was not attracted to a magnet and therefore, would not be affected by it......

WRONG!!!!

Imagine our surprise when the aluminium sheet visibly slowed, barely made it past the magnet and came to a complete stop in about three short swings.

That is the day that I learned the words "eddy current", a lesson I have not forgotten in over 40 years.
A beautiful experiment ...  :)

Offline Nowhere Man

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #106 on: February 22, 2013, 10:13:25 PM »
Demonstration rather than an experiment.

A friend has something similar:  A length of aluminum pipe and a supermagnet.  First, he shows how the magnet won't stick to the outside of the pipe.  Then he holds the pipe vertical and drops the magnet down the middle.  Five seconds later it falls out the bottom.

Fred
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Offline ka9q

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #107 on: February 22, 2013, 10:35:22 PM »
without exception we all said that it would just swing on through because we all knew aluminium was not attracted to a magnet and therefore, would not be affected by it......
I wonder if any answers would have changed had he pointed out that the disk in an ordinary electromechanical utility watt-hour meter is aluminum.

Offline ka9q

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #108 on: February 22, 2013, 10:58:19 PM »
Then he holds the pipe vertical and drops the magnet down the middle.  Five seconds later it falls out the bottom.
This is a very common demonstration in science museum lectures.

Another fun thing often done with eddy currents is to build a large transformer with a long vertical pole-piece and lay aluminum rings on the top of the transformer. When you apply current to the coil, the ring shoots up in the air. I've seen Youtube videos where the rings reach 10-15 m; I think that one charged up a large capacitor bank to something like 750V DC and discharged it into the coil.

One practical application of this effect is the linear induction motor. My all-time favorite amusement park ride, Superman: The Escape, accelerates a car from 0-100 mph (0-44.7 m/s) in 7 s (6.4 m/s2, 0.65 g).

Actually, I'm not totally sure that this ride uses the linear induction motor or the closely related linear synchronous motor, with a permanent magnet rather than a non-magnetic metal plate.

Offline ka9q

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #109 on: February 22, 2013, 11:04:55 PM »
There are two reasons I can think of off the top of my head that it's impossible to use sound to create a colour picture
I've had a color ultrasound movie of my heart. The color was false, of course; it encoded the Doppler shift of the blood moving in the field. Blood approaching the sensor was in red, and blood moving away was blue (I thought it should have been the opposite, but I didn't design it). Cardiologists find this very useful to see how blood is flowing through the heart chambers and valves.


Offline smartcooky

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #110 on: February 23, 2013, 02:19:15 AM »
without exception we all said that it would just swing on through because we all knew aluminium was not attracted to a magnet and therefore, would not be affected by it......
I wonder if any answers would have changed had he pointed out that the disk in an ordinary electromechanical utility watt-hour meter is aluminum.
How many 12/13 year olds would even know what an electrowatthourthingy was in the first place?
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Offline gillianren

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #111 on: February 23, 2013, 02:43:53 AM »
That's his aluminum foil, is it?

¿Qué?

It's a Douglas Adams reference.  Life, the Universe, and Everything.
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Offline smartcooky

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #112 on: February 23, 2013, 03:10:53 AM »
That's his aluminum foil, is it?

¿Qué?

It's a Douglas Adams reference.  Life, the Universe, and Everything.

Ah!. That why it went over my head.

I only ever read the first two books in the Hitch-hiker series.
► What you can assert without evidence, I can dismiss without evidence
► When you argue with idiots you risk being dragged down to their level and beaten with experience.
► Conspiracism is a shortcut to the illusion of erudition

Offline ka9q

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #113 on: February 23, 2013, 06:22:12 AM »
How many 12/13 year olds would even know what an electrowatthourthingy was in the first place?
I did...

Offline Echnaton

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #114 on: February 23, 2013, 08:20:40 AM »
How many 12/13 year olds would even know what an electrowatthourthingy was in the first place?
I did...

Most only really know what it is when they start paying the electric bill.  Then they realize it is a monster that sucks the soul out of your paycheck. 
The sun shone, having no alternative, on the nothing new. —Samuel Beckett

Offline gillianren

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #115 on: February 23, 2013, 11:31:52 AM »
I've had a color ultrasound movie of my heart. The color was false, of course; it encoded the Doppler shift of the blood moving in the field. Blood approaching the sensor was in red, and blood moving away was blue (I thought it should have been the opposite, but I didn't design it). Cardiologists find this very useful to see how blood is flowing through the heart chambers and valves.

They do that on this one, too, but the only thing that gets the false colour is the moving blood.
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Offline Zakalwe

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #116 on: February 23, 2013, 11:36:36 AM »
Then they realize it is a monster that sucks the soul out of your paycheck.


Nah...thats an ex-wife....
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Offline Abaddon

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #117 on: February 23, 2013, 06:14:36 PM »
Then they realize it is a monster that sucks the soul out of your paycheck.


Nah...thats an ex-wife....
I should know, I have one of those.

Offline ka9q

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #118 on: February 23, 2013, 09:43:18 PM »
Most only really know what it is when they start paying the electric bill.  Then they realize it is a monster that sucks the soul out of your paycheck.
And the ones who remember their physics (but not their ethics) may reinvent one of the classic ways to make these meters read low: subject them to a strong static magnetic field to exert drag on the rotating disk.

Offline Echnaton

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Re: Anyone familiar with this 'claim' at Aulis.com?
« Reply #119 on: February 23, 2013, 09:48:24 PM »
Most only really know what it is when they start paying the electric bill.  Then they realize it is a monster that sucks the soul out of your paycheck.
And the ones who remember their physics (but not their ethics) may reinvent one of the classic ways to make these meters read low: subject them to a strong static magnetic field to exert drag on the rotating disk.

Now you tell me.  Just after the electric company has put in a smart meter. 
The sun shone, having no alternative, on the nothing new. —Samuel Beckett