Posted by Christopher (208.143.232.66) on January 22, 2002 at 12:01:23:
In Reply to: Three SMOT theories posted by Davis Landstrom on January 16, 2002 at 04:43:48:
: I wonder if the magnets won't eventually wear out.
I know that cheaper ceramic magnets will eventually 'wear out' - their 'gauss' measurement slowly drops as ferrous metals are moved past them, permanent magnets - Neodymium, SamariumCobalt - are more resistant to this. In reality the magnetism is actually transferred from the magnet to the ferrous material, magnetizing it. Your steel ball will eventually become somewhat magnetic itself and your bar magnets will slightly decrease in strength. This may cause your SMOT ramps or motor rpm/speed to eventually decay.
As far as the magnetic 'energy' being used up... I don't believe that happens. From the little I know about magnetism it appears that you can transfer magnetism, possibly losing some in the transfer process, but not 'use up' magnetism.
I sometimes find it helpful to describe magnets as invisible springs. You could theoretically replace the suspension springs in a car with very high gauss magnets, like poles opposing each other. Most quality springs don't lose all of their 'springyness' unless extremely and repeatedly over-stretched/compressed but with magnets you can't over-stretch/compress, you just leave the influence of the magnetic field.
The 'magnet as invisible spring' model flakes out (at least in my mind) in two areas:
1. When suspended (attracting upwards or lifting.) If you place a magnet on the ground and place a magnet above it, like poles facing each other, it will behave exactly like an invisible spring... but.. if you suspend a weight from a spring it will stretch the spring to some limit point and then bounce around that limit point. This means the spring's pull increases as the weight gets farther away from it. A magnet attracting another magnet (opposite poles of course) or a ferrous weight from above will decrease its pull as the weight gets farther away and increase it's pull as the weight gets closer. This is backwards from a spring.
2. A spring always just compresses if you push on it or stretches if you pull on it. That's just about all it can do. Depending on the material and/or the pole configuration, a magnet may actually help you when compressing (like poles opposing=spring, opposites opposing or ferrous material=opposite of a spring) This is also very un-spring like behavior.
Don't know if this helps or just confuses but it sure is fun to talk about. Oh, and everything I know I learned from Mr. Wizard so if I got anything really wrong here feel free to correct away :-)