I have read lots of articles about permanent magnet motors, some of which claim the possibility and other which refute it. Is it possible to have a permanent magnet motor that runs on the magnetic force of permanent magnets?
[Physics] Has any permanent magnet motor been proven to run
classical-mechanicselectricityelectromagnetism
Related Solutions
Yes, a sheet of a superconducting material will act as a magnetic screen because magnetic fields cannot penetrate into superconductors. Actually a plate of a simple ferromagnet is not a bad magnetic screen and will block most of the magnetic field, though not all. As Jon Custer points out, there is a high relative permittivity ferromagnet called mu metal that is often used for magnetic shielding.
Your second question is a duplicate of Does a permanent magnet loose its magnetism?.
It is a textbook problem to get the magnetic field of a permanent magnet sphere that is perfectly uniform. It turns out it looks exactly like the field of a ideal dipole.
The solution is a bit messy already, but if the magnet has a total magnetic moment of $\mathbf{m}$ and radius $a$, then the magnetic field for $r>a$ is:
$$\mathbf{B}(r>a)=\frac{\mu_0}{4\pi} \left[ -\frac{\mathbf{m}}{r^3}+\frac{3(\mathbf{m}\cdot\mathbf{r})\mathbf{r}}{r^5}\right]$$
If you look at large enough distances $r>>a$, most magnets roughly have fields like that in the above equation. However, when you have a strangely shaped magnet and are looking at the field really close to it, you can get more complex behavior.
See for example: http://farside.ph.utexas.edu/teaching/jk1/lectures/node61.html
Best Answer
Magnetic field, and interactions of atoms with magnetic field, conserve energy, i.e. no net energy gets created at any point. There is not a lot of energy in the field of even a strong permanent magnet. One could, in principle, construct a 'motor' that would demagnetise the magnets somehow, converting the field energy into motion, but it wouldn't be some effective super energy storage or the like, and would run for some time then stop.
I think the reason people turn to magnets when trying to build perpetual motion devices is that it is harder to understand energy conservation in this context, and furthermore it seems more magical. The fact is, the laws governing electromagnetic interactions are very well known, incorporate conservation of energy. There is the point of "what if the scientists are wrong?" Science, indeed can be wrong sometimes. But if this particular knowledge was off by more than utterly microscopic amount, the computer you use to read this message, the communication equipment, the power equipment, the generators, the hard drive in the computer storing this message, and so on, would not have been possible to engineer.