Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: LetoII on 29/03/2012 15:48:58
-
i would like to know some more about superconductivity and my searches havent yet brought me what i was looking for.
when a heavy metal is floating freely on a superconductive track which is NOT flat by has up's and down's in its track then by how much would the height of the floating metal be effected by a downward motion increasing it's speed. in other words: how strong is the resisting force between the metal and the track.
in speeding up a maglev train accelerating to top speed seems to take quite some time, why is this? Is the acceleration rate of the propulsion system so low and is it only achieving high speed through less friction or is there something else going on?
thanks in advance
-
I am no expert in MagLev systems but there are quite a few types I believe, and only a few rely on superconducting elements. I don't think any systems (at least not any commercial systems) use superconductors in the track. The latest Japanese system has superconducting magnets in the train and sequences of coils embedded in the track.
A metal will not suspend itself over a superconductor. A magnet will though, because the magnet's movement will induce eddy currents in the superconductor which, in turn, will oppose the magnet's movement (in this case downwards because of gravity). In fact, as long as some energy is put in, it is not necessary to use a superconductor and any good conductor will demonstrate the effect. This is one of the factors in how a "linear motor" works. To answer your question, the resisting force will depend on the strength of the magnet. If it is too weak compared with its overall mass (including any train sitting on it) then it will be too near the surface to be useful. I guess it would need to be several millimetres away to be safe.
There may be some issues with superconducting materials related to surface effects too - not just lack of perfect smoothness. The superconductivity can be affected by strong fields and/or high current densities, so there are probably a number of factors involved. This may also be a factor in limiting the acceleration, though I had not realised this was an issue. It is the case that when accelerating relative to a track, this is one time when friction helps :-)
-
Your question is not clear Leto. You appear to think that the acceleration of an object is related to friction on some way and that an object on a frictionless bearing should accelerate faster. However the acceleration of any object depends only on the force applied to accelerate it and the only effect that unwanted friction would have is to make it accelerate slower than the ideal value if there was no friction.
There are also very good reasons why train designers would not want a train to accelerate too quickly notably the comfort and stability of the passengers.
One other facto Leto if the track is sloping downhill the accelerating force is the weight of the train reduced by the gradient of the slope. Of it was vertical it would be 1g and horizontal zero most railways have slopes much less than 1 in 50 lats say 1 in 100 so the limit acceleration down the slope is only 1/100 of a g say around 10 cm/sec /sec
-
thanks for all you gave so far, in regard to what i meant to ask with the first part: i'm simply wondering if the distance between the train and the track would become smaller due to the forces aplied by accelerating due to a drop in height or if the resisting field is too powerfull to even mention such a thing.
the second part of my question is simply to gather info on if a maglev system could accelerate alot faster than it does.