“Why do magnets attract ferrous materials yet have no apparent effect on non-ferrous materials? How fast do magnetic fields propagate?
Why do magnets attract ferrous materials yet have no apparent effect on non-ferrous materials?
Magnetic fields attract ferrous metals because the magnetic field lines set up by the magnet create "magnetic domains" within a piece of ferrous metal. The interconnected system of magnet and magnetic domains has less total energy than the magnet alone has. The force you feel between a magnet and a chunk of ferrous metal is the result of the tendency of physical systems to assume the lowest available total energy state. Mathematically, it results from the fact that force is the first derivative of energy with respect to position. Thermodynamically, it is a consequence of Newton's second law.
Non-ferrous metals do not exhibit this "magnetic domain" phenomenon, so magnetic fields have no effect on them, at least when they are at rest with respect to the magnet.
Electrically conductive materials (including metals) are affected by magnetic fields when they are moving. Here is a video that shows this phenomenon, which is called "Lenz's Law."
By the way, a "ferrous metal" is simply a metal that contains a substantial amount of iron (Fe, or "ferrum" in Latin). Other elements exhibit magnetic domain behavior as well, specifically cobalt and (surprisingly) oxygen.
How fast do magnetic fields propagate?
Magnetic fields do not "propagate," at least not in the same sense as photons propagate. That's why the strength of magnetic fields dies off very quickly as you get farther from the source of the magnetic field.
That said, changes in magnetic field strength move from one point within the field to another at the speed of light. This is because magnetic fields, like electric fields, are "carried" by photons.
Under the theory of quantum electrodynamics, every type of field has a corresponding particle that "carries" it.