|MadSci Network: Physics|
Yes, one can, in principle, replace the copper wire in a motor with superconducting material. You would have to go through a significant amount of `engineering' problems, though.
First of all, there is the problem of cooling the motor below Tc during its time of operation. Second, there is the problem of limited current and magnetic field `endurance' of the superconductor. If the current or the magnetic field gets too large, superconductivity will break down, with, depending on the parameters, sometimes hazardous consequences.
Wire made of High-Tc superconductors is available, though I do not know at which price.
The force between a superconductor and a permanent magnet depends on many parameters, including the magnetic moment of th magnet, but also the shape of it, so I cannot give a general answer to that question. The force between permanent magnets of some specific shape has been treated before in this forum, though.
Liquid hydrogen is a somewhat dangerous coolant - mixing it with oxygen in any way would, as you surely know, produce a very efficient explosive. It has a temperature of about 20K, which is unnecessarily low for High-Tc superconductors. Liquid nitrogen is a much better and safer choice here.
Here are some links which may get you going on the subject of superconductivity and its practical applications, including motors and such:
Hope that helps,
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