Inventions

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AuthorTopic: Inventions
Shaper
Member # 73
Profile #50
Thuryl, that would be "Gooble gobble", not "Gobble gobble", according to a quick Google search. Therefore,

zomg turkey
IMAGE(http://www.gotpetsonline.com/pictures-gallery/bird-pictures-breeders-chicks/turkey-pictures-breeders-chicks/pictures/turkey-0001.jpg)

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Posts: 2957 | Registered: Thursday, October 4 2001 07:00
Agent
Member # 5814
Profile #51
quote:
Originally written by Thuryl:

quote:
Originally written by Drow:

"Gobble gobble" just about sums this thread up.
Are we now going to have to start chanting "We will make you one of us" when we welcome new members?

At least it'd be something new. "Leave your sanity at the door" got old a long time ago.
quote:
Originally written by WiKiSpidweb:

I also do some work in a robotics lab, where I'm working on a automated paintball shooting tank. It autonomously tracks targets and shoots them.
And how will you make it only shoot at squirells?

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quote:
Originally written by Kelandon
Well, I'm at least pretty

Posts: 1115 | Registered: Sunday, May 15 2005 07:00
Off With Their Heads
Member # 4045
Profile Homepage #52
quote:
Originally written by *i:

The net consequence is that magnetic fields can do no net work, only electric fields can*.
Something just occurred to me: What you're saying is limited to simple Newtonian equations, right? I mean, one of the problems with magnetism is that permanent magnets don't have simple laws underlying them, because permanent magnetism is a quantum effect.

Because, clearly, a permanent magnet sitting on a table near a small piece of metal can do some work, attracting the metal towards it.

[ Monday, June 19, 2006 07:33: Message edited by: Kelandon ]

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Posts: 7968 | Registered: Saturday, February 28 2004 08:00
Electric Sheep One
Member # 3431
Profile #53
Yeah, he should only have been talking about magnetic fields doing no work on spinless electric charges. A magnetic field that varies in space can indeed do work on a magnetic moment. Lots of kinds of particles have intrinsic magnetic moments because of their spin, which is in some senses a quantum property. And ferromagnetism is indeed a phenomenon of spins.

Even classically, though, *i's remark deserves some comment, because you can make a classical magnetic moment out of moving charges, for instance by running current around a loop.

I have a primitive electric motor which consists of a wire loop free to spin in a frame, with a current driven through the wire by a battery. Nothing happens except for the wire getting warm, until you put a small fridge magnet under the loop. Then it spins like the dickens. It could power a small toy car.

(For the experts: the reason it keeps spinning around, instead of just swinging back and forth because the torque reverses once the loop flips 180 degrees, is that the wire is insulated on one side only, so that the current is blocked and the torque ceases when it would otherwise be reversed. Half of every revolution by the loop is unpowered, but when it does get torque, it always gets it in the same direction.)

The fact that you do need the battery indicates that the magnet is not driving the loop around all by itself. The magnet does not wear out or run down, though the battery does. And ferromagnetism is only involved here in the fridge magnet that creates the magnetic field; the motion of the loop is just about moving charges, not spin. So since *i is quite right about magnetic fields doing no work on moving charges, the magnet does no work in making the loop spin.

Yet the magnet does make the loop spin, in the sense that the loop spins if and only if the magnet is present; and the spinning loop can certainly do work itself, so work is being done on it by something.

I leave the resolution of this paradox as an exercise for the reader.

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Posts: 3335 | Registered: Thursday, September 4 2003 07:00
Law Bringer
Member # 335
Profile Homepage #54
I invented a resolution to the paradox.

—Alorael, who won't reveal it until he has it firmly copyrighted, patented, trademarked, and copy protected.
Posts: 14579 | Registered: Saturday, December 1 2001 08:00
Infiltrator
Member # 3441
Profile Homepage #55
quote:
And how will you make it only shoot at squirells?
I don't know that we have the capability to distinguish different animals from one another. It is currently programmed to only shoot blue objects. But that's because the really good programmers aren't working on it. This robotics club does some serious stuff, such as the DARPA Grand Challenge, as well as national UAV, unmanned sub, and unmanned ground vehicle competions, where they have to recognize complex obstacles and avoid them.
Our current simplistic setup works by taking the data from the camera and turning it into a 2D array of RGB values, the centroid of the blue values is found and the turret is moved until the centroid is in the center of the camera, which is aligned with the barrel of the gun. This is pretty much the most basic way imaginable to visually track something, and adjustments need to be made for situations where there are multiple objects in view, which confuses the above mentioned algorithm.
I can't tell you much more than that, since I've been working on the mechanical side of the project.

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"As our circle of knowledge expands, so does the circumference of darkness surrounding it." --Albert Einstein
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Posts: 536 | Registered: Sunday, September 7 2003 07:00
The Establishment
Member # 6
Profile #56
quote:
Something just occurred to me: What you're saying is limited to simple Newtonian equations, right?
No, what I said applies to relativity and quantum mechanics. While it is true, that ferromagnetism is a quantum property, the fundamental idea that magnetic forces do no work to a free charge is always true.

Wikipedia sums up the argument best in Griffiths:

quote:
Because this is a cross product, the force is perpendicular to both the motion of the particle and the magnetic field. It follows that the magnetic force does no work on the particle; it may change the direction of the particle's movement, but it cannot cause it to speed up or slow down.

This might give you pause: Simple bar magnets seem to be entirely able to pick up small metal objects, which certainly seems to require that they do work on those objects. As David Griffiths points out in his textbook Introduction to Electrodynamics, this law is absolute - the magnetic field doesn't do any work. However, quite like the normal force of an inclined plane, which also can't do work, the magnetic field can redirect the efforts of existing forces, and then those forces can indeed do work in the relevant direction.
While it is true things like ferromagnetism have only a quantum mechanics description, Maxwell's equations and the Lorentz Force law are still valid.

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Your flower power is no match for my glower power!
Posts: 3726 | Registered: Tuesday, September 18 2001 07:00
Law Bringer
Member # 6785
Profile #57
quote:
Originally written by WiKiSpidweb:
I also do some work in a robotics lab, where I'm working on a automated paintball shooting tank. It autonomously tracks targets and shoots them.

And how will you make it only shoot at squirells?

Define squirrels as the targets, then all the targets that are hit squirrels by definition. Just because everyone else thinks that you are targetting everything is immaterial.
Posts: 4643 | Registered: Friday, February 10 2006 08:00
Guardian
Member # 6670
Profile Homepage #58
By WKS:
quote:
I don't know that we have the capability to distinguish different animals from one another. It is currently programmed to only shoot blue objects. But that's because the really good programmers aren't working on it. This robotics club does some serious stuff, such as the DARPA Grand Challenge, as well as national UAV, unmanned sub, and unmanned ground vehicle competions, where they have to recognize complex obstacles and avoid them.
We have a similar set-up at my uni. It's an Segway that tracks and kicks soccer balls. You quickly discover that it's a bad idea to walk into that particular lab with a brightly coloured shirt on. The bot attempts to close the distance between itself and the perceived ball in the distance as quickly as possible.

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I prefer my homicidal robots quasi-sentient. At least then you can reason with them.
Posts: 1509 | Registered: Tuesday, January 10 2006 08:00
Electric Sheep One
Member # 3431
Profile #59
quote:
Originally written by *i:

While it is true things like ferromagnetism have only a quantum mechanics description, Maxwell's equations and the Lorentz Force law are still valid.
But the Lorentz force isn't the only force. There is also the magnetic moment term in the Hamiltonian, \vec{\mu}\cdot\vec{B}. Check out the non-relativistic limit of the Dirac or vector Klein-Gordon equations to see that this term is really there. If this term is not constant, it exerts a force.

Classical spinless moving charges can produce magnetic moments, leading to the paradox posed above, in which magnetic fields do no work but do enable work to be done. But relativity and quantum field theory together give particles intrinsic magnetic moments, and so real particles do experience non-Lorentz forces from magnetic fields, which can do work.

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We're not doing cool. We're doing pretty.
Posts: 3335 | Registered: Thursday, September 4 2003 07:00
Law Bringer
Member # 2984
Profile Homepage #60
quote:
Originally written by WiKiSpidweb:

[QUOTE]
Our current simplistic setup works by taking the data from the camera and turning it into a 2D array of RGB values, the centroid of the blue values is found and the turret is moved until the centroid is in the center of the camera, which is aligned with the barrel of the gun. This is pretty much the most basic way imaginable to visually track something, and adjustments need to be made for situations where there are multiple objects in view, which confuses the above mentioned algorithm.

Now the only remaining problem is to breed blue squirrels...

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Posts: 8752 | Registered: Wednesday, May 14 2003 07:00
Off With Their Heads
Member # 4045
Profile Homepage #61
quote:
Originally written by *i:

However, quite like the normal force of an inclined plane, which also can't do work, the magnetic field can redirect the efforts of existing forces, and then those forces can indeed do work in the relevant direction.
If the magnetic field isn't doing any work when a bar magnet picks up a ball bearing, then which force is doing that work? The electric force? And how does it do it?

I know that friction is proportional to the normal force, so I get the analogy, but I thought that the only relationship between electric fields and magnetic fields (classically) was that a change in one creates the other, and I don't think that a bar magnet creates a changing magnetic field, so I'm a bit befuddled.

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Arancaytar: Every time you ask people to compare TM and Kel, you endanger the poor, fluffy kittens.
Smoo: Get ready to face the walls!
Ephesos: In conclusion, yarr.

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The Archive of all released BoE scenarios ever
Posts: 7968 | Registered: Saturday, February 28 2004 08:00
Electric Sheep One
Member # 3431
Profile #62
quote:
Originally written by Wikipedia:

This might give you pause: Simple bar magnets seem to be entirely able to pick up small metal objects, which certainly seems to require that they do work on those objects. As David Griffiths points out in his textbook Introduction to Electrodynamics, this law is absolute - the magnetic field doesn't do any work. However, quite like the normal force of an inclined plane, which also can't do work, the magnetic field can redirect the efforts of existing forces, and then those forces can indeed do work in the relevant direction.
Hmmm, this seems to be a limitation of Wikipedia. The non-constant field of a bar magnet pulls on nuclear and electronic spins in a ferromagnetic material, and this does do work. I don't have Griffiths at hand to judge whether the error is in Griffiths or by the Wikipedia writer.

The resolution to my paradox in the absence of spin, I have just realized, is startlingly simple. If we have a system of more than one spinless charged particles, the total force on the system's center of mass, from all the Lorentz forces on the individual particles, will in general do work on the center of mass. (It is easy to work out what 'in general' means for the case of two particles in a constant magnetic field; it really does mean, 'except in a few very special cases'.)

For spinless particles the magnetic field still does no work on the system as a whole. This just means that it does negative work on the relative co-ordinates among the particles. This may sound strange, but there is absolutely nothing odd about it, really. Suppose two oppositely charged particles of equal mass begin moving towards each other at equal speed. The center of mass has zero kinetic energy (it is not moving). In a constant magnetic field the two particles move in circles at the same rate (and at constant velocity) but in opposite orbital directions. So after 1/4 of a circle each, they are moving in the same direction. The center of mass now has positive kinetic energy, even though the total kinetic energy has not changed. The relative co-ordinate -- the separation between the two particles -- is at this moment not changing at all, so it has zero kinetic energy. It began with positive kinetic energy; it has received negative work, from the magnetic field.

So can a magnetic field do work on a composite object? To remove the issue of spin, which does allow magnetic fields to do work quite unambiguously, we can rephrase the question as, Can the Lorentz force do work on a composite object? And now the answer depends entirely on what you mean by the object. If you mean its center of mass, then the answer is yes, in spite of Griffiths and anybody else. If you mean the total work done on all of the object's components, then the answer is no.

Since the answer thus depends on terminology, you can have it either way you want, if you really want. I'd submit, though, that in cases where all of an object's relative co-ordinates are held tightly together by non-magnetic forces, but the center of mass is comparatively very free, then the practical question, and the one that most people would naturally want to ask, is about the work done on the center of mass. Internal forces do not affect the center of mass at all, so the magnetic force is the only explanation available for acceleration or deceleration of the center of mass.

[ Tuesday, June 20, 2006 12:31: Message edited by: Student of Trinity ]

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Posts: 3335 | Registered: Thursday, September 4 2003 07:00
Lifecrafter
Member # 34
Profile Homepage #63
I made a flute that played itself. Needless to say, it totally blew.

[ Tuesday, June 20, 2006 19:01: Message edited by: Robinator, #034 ]

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Posts: 702 | Registered: Wednesday, October 3 2001 07:00
The Establishment
Member # 6
Profile #64
quote:
Classical spinless moving charges can produce magnetic moments, leading to the paradox posed above, in which magnetic fields do no work but do enable work to be done. But relativity and quantum field theory together give particles intrinsic magnetic moments, and so real particles do experience non-Lorentz forces from magnetic fields, which can do work.
You are correct and Griffiths is as well. To clarify my last post, work cannot be done on a free charge, but can on a magnetic moment. There is the key distinction. The force felt by the moment is:

F = mu*dB/dx

F = force
mu = magnetic moment
B = magnetic field

The work done rotates the magnetic moment along the magnetic field. The complication from quantum mechanics lies in the intrinsic magnetic moments in particles. The classical formulation is correct if one assumes a dipole moment.

[ Tuesday, June 20, 2006 20:52: Message edited by: *i ]

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Your flower power is no match for my glower power!
Posts: 3726 | Registered: Tuesday, September 18 2001 07:00
Electric Sheep One
Member # 3431
Profile #65
The magnetic moment force can also just speed particles up or slow them down, like gravity or electrostatic force. If the direction of B is constant, then the projection of the intrinsic magnetic moment along the magnetic field direction will not change either. So the interaction energy \mu\cdot B is then in this case simply a potential acting on the particle's position. Magnetic traps for neutral atoms work this way.

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We're not doing cool. We're doing pretty.
Posts: 3335 | Registered: Thursday, September 4 2003 07:00
Master
Member # 5977
Profile Homepage #66
quote:
Originally written by Robinator, #034:

I made a flute that played itself. Needless to say, it totally blew.
Is it in the same family of the self-playing piano, of which I forgot its name?

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Posts: 3029 | Registered: Saturday, June 18 2005 07:00
Agent
Member # 6581
Profile Homepage #67
Inventions? I would make an implant: a computer IN your arm that recarge itself with your physical energy.

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Posts: 1310 | Registered: Tuesday, December 20 2005 08:00
Law Bringer
Member # 4153
Profile Homepage #68
quote:
Originally written by MagmaDragoon:

Inventions? I would make an implant: a computer IN your arm that recarge itself with your physical energy.
Yay! Let's make modern technology even more of a parasite with respect to our lives!

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Posts: 4130 | Registered: Friday, March 26 2004 08:00
Lifecrafter
Member # 6403
Profile #69
Why not? If people want it, let them go ahead and get it.

Myself, I've always wanted an mp3 player embedded into my body so I would be able to listen to music at all times.

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Posts: 883 | Registered: Wednesday, October 19 2005 07:00
Lifecrafter
Member # 34
Profile Homepage #70
I invented the dictionary. My parents said they were so proud they couldn't put it into words.

[ Wednesday, June 21, 2006 19:05: Message edited by: Robinator, #034 ]

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Frisbeetarianism is the belief that when you die, your soul goes up on the roof and gets stuck.

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Posts: 702 | Registered: Wednesday, October 3 2001 07:00

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