I wanted to explain this very basic phenomenon in some detail. I should start a new section on general electromagneto-dynamics, but .. I might just save it for the book .. In any case, this is what goes on.
Special thanks to "Adam" for this opportunity to explain this ..
Take a coil that you can push a round cylinder magnet thru. The round magnet has polarity on its ends. Its a cylinder shape. A coil without so many windings won't resist so much and you can push the magnet thru easily. Lots of windings offer more resistance when the coil is connected in a circuit, and it's harder to push the magnet thru as it is offering more resistance due to the induced magnetic field in the coil. That is what resistance is. The induced magnetic field in the coil from pushing the magnet through it, is induced in the SAME polarity as the magnet. The reason for this, is that once you start pushing the magnet through the coil, electricity (magnetic current) flows through the entire length of wire, formed into an unbroken circuit; and since electricity flows through the coil of wire, it creates a magnetic field of it's own. So the north end of the magnet has to push against the north induced magnet in the coil, up ahead of the magnet being pushed through. It thus requires force to push the magnet through the coil. If the coil wasn't connected in a circuit, no electricity would flow, and no induced electromagnet would offer any resistance.
But if the magnet isn't moving, or lets say you have an iron core, then the coil induces the core in the same polarity when you turn on the electromagnet.
You also magnetize the core in the process. If you turn the field off, the opposite polarity of collapse attracts to the iron magnet with no resistance.
If you reverse the polarity of the coil instantly, it compresses the field and collapses the prior field, sparks, and remagnetizes the core in the new polarity. Again, the reversal is attractive. Your not in opposition unless you push north to north (or south to south). If you push yer rod magnet thru the coil, you induce the same polarity in the coil so it pushes like pole against like pole.
Pushing opposing poles together is not resistive but attractive.
Any resistance is only magnetic resistance of similar poles because they push against each other. Stick two magnets together north pole to north pole. It takes a lot of force. Push the north pole to south pole instead and it takes no force, it is negative force! It helps you along so that instead of applying force to push them together, it jerks it out of your hand.
Positive force pushes an object to move. Zero force is rest. Negative force means you have to pull the object back to hold it to maintain it at rest.
An eddy current is spin not opposition. An eddy current is induced motion. It is byproduct of force. The only thing that is resistive is the inertia of motion itself requiring more force to speed up the eddy or less force to slow it down.
Eddy currents also act as gears to maintain the current in motion and is nothing more than the circulation field of motion itself. The eddy current is harnessed to make a rotor move in a motor, for example. Magnetic spin and circulation is the nature of the wave in polarity.
The rod magnet pushing thru a coil is hard to push (resistance) because it induces the SAME polarity in the coil. If it induced the opposite polarity, there would be negative resistance, moving faster than the applied force. There wouldn't be resistance.
If you push the north end of a rod magnet thru a coil and it induces the opposite polarity, then it would be easy because you'd be inducing a south pole in front of the north pole of the magnet which means it would pull itself along without you pushing.
A coil wound around an iron core. Magnetize and hold. Coil north pole is now the iron rod's north pole. Release and collapse the field. Now coil field is in opposite polarity, and opposite poles attract. That speed force creates a high volt flyback because it moves at higher frequency therefore higher volts. Harness in a spark gap.
Without an iron core...
The electromagnetic coil is charged then released. The magnetic field holds itself in resonance as it collapses not in opposition to itself but attractively to itself, BECAUSE the polarity is reversed.
But the collapse collapsing thru its own magnetic field raises its volts thru magnetic resonance. But the collapse occurs at light speed - the speed of electromagnetic propagating waves, and the speed of electromagnetic collapse. It is the magnetic field that collapses. The moving magnetic field induces current to flow. But since the circuit is broken to collapse the magnetic field, there is no resistance possible because there is no circuit that resists itself.
The buildup of volts however is still being induced in the coil of wire, but instead of current flowing thru all the windings (from the start of the wire through the entire length of the wire to the finish) to form a magnet, the magnet induces current thru the entire length of those coil windings all at once.
That pushes high volts, determined by the windings out the poles of the magnet at right angles to the direction of the magnetic collapse. That is a force of magnetic collapse and release but a force of electric volt build-up, but it does not resist its own movement until the circuit is connected again.
The spark discharge reconnects the circuit. But by then, your original current in the wires is way distorted and is only connected in a circuit by the magnetic field itself, no longer coursing thru the entire length of the windings. It is no longer acting in transverse at that point, flowing in circles for magnetic poles to form out the ends, but in PARALLEL, shorting right thru the wire insulation but without burning the insulation. It's cold and does not burn out the wires.
That entire action is not only superconductive, but becomes a parallel energy (magneto-electrostatic), with negative resistance - negative energy.
If you use a coil wound around another coil (primary and secondary coils), it's easier.
A coil is wound, and another secondary coil wound over the top. The first coil is energized, but the secondary coil goes to a spark gap. When the first coil collapses (circuit is broken), the rapid magnetic collapse induces all the wires in the secondary winding at once. In that squeezing effect of rapid magnetic motion, the voltage produce compounds upon itself per the number of windings in the secondary coil, conducting a high voltage that can be harnessed in a spark gap.
Again, the action is superconductive, meaning it does not resist its own motion. As the magnetic field collapses in the primary coil, the secondary coil does not hold back the collapse; and since the primary coil circuit is broken to initiate collapse, there is no resistance to its own collapse. That's why the high volt spark exists to begin with, because there is no resistance; the magnet is free to collapse at the speed of its own wave-propagation, conventionally called the "speed of light;" however, electrostatic waves in parallel travel a little faster.
Electromagnetic wave propagation: 186,000 miles per second (transverse wave; electric and magnetic aspects at right angles)
Electrostatic wave propagation: 220,000 miles per second (parallel wave; longitudinal)
General note: I think it's almost time for a total re-write of all this. I haven't looked at the Tesla Engineering Physics page in a long time, and wanted to put right up at the top that the spark is a requirement for magneto-electrostatic energy; and negative energy is equivalent to magneto-electrostatic energy. However there is an exception to the rule. The collapse of the electromagnetic field initiates the spark, but also initiates a voltage spike. It is the collapse of the field which is the foundation of Tesla energy; however the presence of a spark gap in the system does indeed change the nature of the entire energy throughout the entire system. The only exception to the rule is when a static charge is built up due to a magnetic collapse which changes the nature of the energy in a system. ... Also remember: The unity of light is magneto-electrostatic unity energy; and light is the unity of all matter.
Also note: There is a difference between a resonance coil, which is a single layer of coil windings, and an electromagnet, which are multiple layers of windings on top of each other. The coil windings of the Tesla Generator on the Tesla/Free Energy page are electromagnet windings, NOT resonance coil windings. Induction coils and spark collapses are generated by electromagnet coil windings, but resonated through resonance coil windings.
As far as a resonance coil goes:
The resonance coil collapses in the opposite polarity of the applied charge. An impulse wave is sent to one end of the coil like a rail gun. A spark gap at both ends will only spark at one end, which is one of the concepts of the Tesla tower. It's a static charge in nature because it conducts to air -- a bare-metal plate will conduct a static charge to air; BUT, the direction of the magnetic field collapse will conduct that magneto-static charge in a vacuum.
Additionally: resonance coils work together to amplify energy as explained on the Tesla Engineering Physics page. New developments from a private group have successfully amplified energy from the wall socket (standard AC) to about 800% more output than input, stable. The concept is easy enough. Power runs to a resonance coil, then to capacitors, which amplify the magnetic field and raise the frequency throughout the circuit. A secondary coil then resonates with the primary at the same frequency (for resonance to take place), as the amplified energy from the capacitors are run back through the circuit. The secondary coil picks up the excess energy from the primary coil, and feeds it back through the primary coil. The capacitors however play a major role. The amplified output is stepped back down to usable frequency, and the output amps are much greater than the input amps, while the volts are not compromised, meaning amplification of both amps and volts.
See the Construction Blog page, the post titled "Negative Energy Construction Notes" and the comments on that article for corrections and additional clarity.