I agree, perpetual motion is the first thing that came to my mind, thinking back about that classroom project, all those years ago in grade school.
However the key word, as you said, is USEFUL! Something, after all, had to MAGNETIZE the magnet, to spin the needle, to get the current from. We used to magnetize screwdrivers in electrical shop, in high school, by wrapping a multiple coil of wire around the metal tip, connect both ends of the wire to a simple electrical appliance plug, and quickly shove it into the outlet, tripping the breaker.
The current surge would align the magnetic polarity of the previously random iron atoms in a straight line resulting in a magnetic tip. Not a very strong magnetic tip to be sure, and the magnetism did fade over time. I imagine when industry magnetizes tools commercially, it must really require a lot of juice.
So a LOT of current had to go in to the magnet, to magnetize it, to get a minute bit back out of the spinning "mass of metal". Not efficient at all, and not practically feasible, and definitely NOT perpetual motion. Energy goes in, not so much comes back out. It just works.......barely.
But remember, this is 150 year old Sci-Fi, even if it were impossible, it wouldn't matter. It didn't have to be efficient, just be somewhat feasible, and if not that, at least imaginable. We can all hope that something that dosn't work very good (or even exist,) today, can be made to work better (or invented)tomorrow.
If I remember correctly, Nemo's Nautilus ran on electricity derived from sea water. The was proven to be possible, in the last 50 years I think, just not efficient. More juice has to go into the extraction process than you get back, so the premise of the Nautilus' power supply was sound, it just couldn't work like it was implied.
So again, I agree, no free ride from Mother Nature, "something for nothing," is indeed impossible....
so far!
reply
share