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 2011-08-03, 21:55 #1 Flatlander I quite division it     "Chris" Feb 2005 England 31×67 Posts Explanation for simpleton please. Never seen this effect before: http://www.videobash.com/video_show/...per-pipe-36101 What's going on man? (Note the thread title. )
2011-08-03, 22:49   #2
davieddy

"Lucan"
Dec 2006
England

647410 Posts

Quote:
 Originally Posted by Flatlander Never seen this effect before: http://www.videobash.com/video_show/...per-pipe-36101 What's going on man? (Note the thread title. )
Faraday: moving magnet induces current in the copper.

Lenz' (aka Sod's) Law: current flows so as the oppose the motion inducing
it (via the magnetic field it produces).

(Neither the clearest nor most spectacular demonstration I've seen).

David

 2011-08-04, 03:13 #3 wblipp     "William" May 2003 New Haven 23·103 Posts What am I supposed to see? I see that he drops a magnet down a copper tube and it rattles a few times before it falls out. Is the rattling the amazing effect? Is there something else I didn't notice?
2011-08-04, 05:06   #4
Uncwilly
6809 > 6502

"""""""""""""""""""
Aug 2003
101×103 Posts

2·32·563 Posts

Quote:
 Originally Posted by wblipp What am I supposed to see? I see that he drops a magnet down a copper tube and it rattles a few times before it falls out. Is the rattling the amazing effect? Is there something else I didn't notice?
The magnets don't accelerate at 1g, rather they fall at a much slower rate. That is what you were supposed to notice.

To answer the question posed by the OP:
The magnets are moving by a conductor, this generates electrical current in the conductor. This causes physical resistance to the motion of the magnets. That is why it takes real work to turn a generator. The fact that they are strong magnets and they are shaped like the pipe enhances the presentation.

2011-08-04, 05:33   #5
LaurV
Romulan Interpreter

"name field"
Jun 2011
Thailand

22×11×223 Posts

Quote:
 Originally Posted by wblipp What am I supposed to see? I see that he drops a magnet down a copper tube and it rattles a few times before it falls out. Is the rattling the amazing effect? Is there something else I didn't notice?
It is the speed you did not notice. From the law of conservation of energy (don't know if it is the right English name for it, just word by word translation from my own language) if you drop a body in gravitational field, it will move accelerated down (with G, gravitational attraction) such as its energy is always constant.

In the upper position the body has a "position energy" which is a product between its mass, its height from the center of the earth, and G (P=m*g*h1), and it has a "moving energy" (say it K from kinetic energy) which is equal to 0, because the body does not move. So, its total energy is E=P+K=mgh1+0=mgh.

Assuming you drop this body (no copper pipe) free fall, till it reaches a lower height h2 (floor level). In this second position the body will have the same energy, because you can not create energy from nothing, or destroy energy. But now the body is moving, so some of its potential (position) energy is transformed into kinetic energy. You have now E=mgh2+mv2/2.

You can solve the ecuation mgh1=mgh2+mv2/2 for v and see what speed the body will have when reach the h2 point (not the simpler way, but in line with the example). You get v=$\sqrt{2g(h_1-h_2}$

If the difference between h1 and h2 is 1 meter, the body will "hit" the floor with about 4.5 meter per second (calculated in my mind, forgive me if I am wrong), and the "fall" will take (from the speed law, here v=gt) about 450 milliseconds. So the body will "hit" the floor "hard", its energy will be transformed in "deformation energy", "heat", etc.

Now if you drop that body into a copper tube, as in the video, and the body has magnetic properties, any magnet moving around a copper (metalic) object will induce electrical currents into that object. So, our magnet will lose some of its energy, that will be transformed into electrical currents inside of the copper tube (at the end into the heat, yes, the temperature of the copper pipe will increase few milli/mico/nano-degrees every time the magnet drops, hehe).

So, E=P+k, what kind of energy is the body losing? Its potential energy is the same with or without copper tube, I mean, the energy in h1 is always mgh1, with or without copper tube, and the energy in h2 is mgh2, with or without copper tube. So, the body loses its kinetic energy, K=mv2/2. But it does not loses its mass, that is always constant. So, it follows that the magnet is losing its speed. And the falling time increases. Depending of the magnet and copper tube, the speed of the magnet when it hits the floor can be quite small (in the video is about half and the falling time is twice longer). The magnet is falling "slow motion". But there is no mystery in it. If you replace the copper pipe with a solenoid and put some (external) current through it, you can make the magnet move "snail speed", and eventually in both directions. That is how actuators work.

Someone will say that the additional energy come from the magnet (that is losing in this way its magnetic "abilities" in time, like 40 years or so) but that is bullshit. One of my eternal source of fun was the guys on youtoube (or else on the web) trying to realize a "magnetic motor" (to produce energy from solely the energy stored into permanent magnets).

edit: whoops, too long post, just saw now that Uncwilli was much faster (writing from job, interrupted many times).

Last fiddled with by LaurV on 2011-08-04 at 05:36

2011-08-04, 11:27   #6
davieddy

"Lucan"
Dec 2006
England

2×3×13×83 Posts

No problem is so difficult that it cannot be made to seem
completely intractable with a few pages of Wiki-style waffle

David

PS @LaurV: yes I did note your edit!

Quote:
 Originally Posted by davieddy Faraday: moving magnet induces current in the copper. Lenz' (aka Sod's) Law: current flows so as the oppose the motion inducing it (via the magnetic field it produces). (Neither the clearest nor most spectacular demonstration I've seen). David
Quote:
 Originally Posted by Uncwilly The magnets don't accelerate at 1g, rather they fall at a much slower rate. That is what you were supposed to notice. To answer the question posed by the OP: The magnets are moving by a conductor, this generates electrical current in the conductor. This causes physical resistance to the motion of the magnets. That is why it takes real work to turn a generator. The fact that they are strong magnets and they are shaped like the pipe enhances the presentation.
Quote:
 Originally Posted by LaurV It is the speed you did not notice. From the law of conservation of energy (don't know if it is the right English name for it, just word by word translation from my own language) if you drop a body in gravitational field, it will move accelerated down (with G, gravitational attraction) such as its energy is always constant. In the upper position the body has a "position energy" which is a product between its mass, its height from the center of the earth, and G (P=m*g*h1), and it has a "moving energy" (say it K from kinetic energy) which is equal to 0, because the body does not move. So, its total energy is E=P+K=mgh1+0=mgh. Assuming you drop this body (no copper pipe) free fall, till it reaches a lower height h2 (floor level). In this second position the body will have the same energy, because you can not create energy from nothing, or destroy energy. But now the body is moving, so some of its potential (position) energy is transformed into kinetic energy. You have now E=mgh2+mv2/2. You can solve the ecuation mgh1=mgh2+mv2/2 for v and see what speed the body will have when reach the h2 point (not the simpler way, but in line with the example). You get v=$\sqrt{2g(h_1-h_2}$ If the difference between h1 and h2 is 1 meter, the body will "hit" the floor with about 4.5 meter per second (calculated in my mind, forgive me if I am wrong), and the "fall" will take (from the speed law, here v=gt) about 450 milliseconds. So the body will "hit" the floor "hard", its energy will be transformed in "deformation energy", "heat", etc. Now if you drop that body into a copper tube, as in the video, and the body has magnetic properties, any magnet moving around a copper (metalic) object will induce electrical currents into that object. So, our magnet will lose some of its energy, that will be transformed into electrical currents inside of the copper tube (at the end into the heat, yes, the temperature of the copper pipe will increase few milli/mico/nano-degrees every time the magnet drops, hehe). So, E=P+k, what kind of energy is the body losing? Its potential energy is the same with or without copper tube, I mean, the energy in h1 is always mgh1, with or without copper tube, and the energy in h2 is mgh2, with or without copper tube. So, the body loses its kinetic energy, K=mv2/2. But it does not loses its mass, that is always constant. So, it follows that the magnet is losing its speed. And the falling time increases. Depending of the magnet and copper tube, the speed of the magnet when it hits the floor can be quite small (in the video is about half and the falling time is twice longer). The magnet is falling "slow motion". But there is no mystery in it. If you replace the copper pipe with a solenoid and put some (external) current through it, you can make the magnet move "snail speed", and eventually in both directions. That is how actuators work. Someone will say that the additional energy come from the magnet (that is losing in this way its magnetic "abilities" in time, like 40 years or so) but that is bullshit. One of my eternal source of fun was the guys on youtoube (or else on the web) trying to realize a "magnetic motor" (to produce energy from solely the energy stored into permanent magnets). edit: whoops, too long post, just saw now that Uncwilli was much faster (writing from job, interrupted many times).

Last fiddled with by davieddy on 2011-08-04 at 11:33

2011-08-04, 13:15   #7
davieddy

"Lucan"
Dec 2006
England

2×3×13×83 Posts

Quote:
 Originally Posted by Flatlander Never seen this effect before: http://www.videobash.com/video_show/...per-pipe-36101 What's going on man? (Note the thread title. )
Old speedometers used to work like this:

The needle on the dial was connected to a copper disc on a spiral spring.
The wheels rotated a bar magnet close to the disc.
The faster it turned, the greater the torque on the disc, and the further
the spring and needle on the dial were twisted.

I expect this may have been superceded in this digital age, but
generating a voltage proportional to speed may still enter into it somewhere.

On second thoughts, displaying RPM graphically ain't exactly rocket science!

David Eddy Current

PS RPM of wheels as a measure of vehicle speed depends on
tyre thickness. Do they use an optical mouse to measure road
speed directly these days?

Last fiddled with by davieddy on 2011-08-04 at 13:41

 2011-08-04, 18:46 #8 davieddy     "Lucan" Dec 2006 England 145128 Posts Spin Offs from experiments A demonstration of e/m levitation we used to do consisted of placing a coil with AC current at the base of a retort stand. When we dropped an aluminium(sic) ring down, it remained suspended a few cm above the coil. What eventually intrigued us (teachers) more was that when you dropped the ring on the retort stand, it often slowly worked its way down in a narrow-pitched helical motion*. I amused myself by working out the "How, Why and Wherefore" thereof. Joe Hatton (Oxford tutor) thought classical mechanics was as dull (old hat) as ditchwater. David *and (no coil in place) bounced when it hit the bottom. Last fiddled with by davieddy on 2011-08-04 at 18:51
2011-08-05, 03:01   #9
LaurV
Romulan Interpreter

"name field"
Jun 2011
Thailand

231248 Posts

Quote:
 Originally Posted by davieddy On second thoughts, displaying RPM graphically ain't exactly rocket science!
Fully agree on that and everything you said (except quotes of quotes of quotes of quotes, that makes the text more difficult to read, I would suggest not to include the quotation marks when you reply to the last post). For cars for example, graphical (and generally digital) RPM display is not a big deal, the deal is the mileage (because the mile-meter has to record even when you push your car and no battery connected, or when the police truck is taking out your car from the wrong parking place, etc). For that there will always be some magnets and some disks or metal scrap around the wheels, on the exactly same fashion that you described. Can't get rid of them.

2011-08-05, 10:12   #10
davieddy

"Lucan"
Dec 2006
England

2·3·13·83 Posts

Quote:
 Originally Posted by LaurV Fully agree on that and everything you said (except quotes of quotes of quotes of quotes, that makes the text more difficult to read, I would suggest not to include the quotation marks when you reply to the last post).
Yep. Careful attention to grammar, capitals, parentheses, spelling and
punctuation just confuses people.
I am trying to learn from the likes of sm88, cmd and your good self

David

2011-08-05, 10:25   #11
davieddy

"Lucan"
Dec 2006
England

2×3×13×83 Posts

Quote:
 Originally Posted by LaurV the deal is the mileage (because the mile-meter has to record even when you push your car and no battery connected, or when the police truck is taking out your car from the wrong parking place, etc).
What effect does reversing have on the milometer?

David

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