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Introduction
The principle of a magnet train is that floats on a magnetic field and is propelled by a linear induction motor.They follow guidance tracks with magnets.These trains are often refered to as Magnetically Levitated trains which is abbreviated to Maglev.Though maglevs don’t use steel wheel on steel rail，the dictionary definition of a train is a long line of vehicles travelling in the same direction—it is a train.
Operation
A maglev train floats about 10mm above the guideway on a magnetic field.It is propelled by the guideway itself instead of an onboard engine by changing magnetic fields.Once the train is pulled into the next section the magnetism switches so that the train is pulled on again.The electro-magnets run the length of the guideway.
Advantages
The primary advantage is maintanance.Because the train floats along there is no contact with the ground and therefore no need for any moving parts.Therefore there are no components that would wear out.This means in theory trains and track would need no maintanence at all.The second advantage is that because maglev trains float，there is no friction.Note that there will still be air resistance.A third advantage is less noise，because there are no wheels running along there is no wheel noise.However noise due to air disturbance still occurs.The final advantage is speed，because of the three previous listed it is more viable for maglev trains to travel extremely fast，i.e.500km/h.Although this is possible with conventional rail it is not economically viable.Another advantage is that the guideway can be made a lot thicker in places，e.g.after stations and going uphill，which would mean a maglev could get up to 300km/h in only 5km where presently takes 18km.Also greater gradients would be applicable.
Disadvantages
There are several disadvantages with maglev trains.Maglev guide paths are bound to be more costly than conventional steel railways.The other main disadvantage is lack with existing infrastructure.For example if a high speed line between two cities is built，then high speed trains can serve both cities but more importantly they can serve other nearby cities by running on normal railways that branch off the high speed line.The high speed trains could go for a fast run on the high speed line，then come off it for the rest of the journey.Maglev trains wouldn’t be able to do that，they would be limited to where maglev lines run.This would mean it would be very difficult to make construction of maglev lines commercially viable unless there were two very large destinations being connected.Of the 5，000km that TGV trains serve in France，only about 1，200km is high speed line，meaning 75％ of TGV services run on existing track.The fact that a maglev train will not be able to continue beyond its track may seriously hinder its usefulness.
Comparison with Conventional Trains
As regards energy consumption maglev trains are slightly better off than conventional trains.This is because there is no wheel-on-rail friction.That said the vast majority of resistive force at high speed is air resistance（often amounting to several tons），which means the energy efficiency of a maglev is only slightly better than a conventional train.
German engineers claim also that a maglev guideway takes up less room and because greater gradients are acceptable there is not so much cuttings and embankments，meaning a new guideway would be less disruptive to the countryside than a new high speed conventional railway.
Maglev may become the preferred path for new high speed railway lines though it would depend whether or not services were needed to extend beyond a high speed line.For example，if you have 300km of conventional track between two cities cleared for over 200km/h but there was a 60km long section only cleared for 80km/h then it would make sense to build a new high speed（300km/h）line for the 60km distance.If a maglev train were to be used a track of 300km long would have to be built.However if there is no existing rail network（only the case in the USA）then it makes sense to build a maglev line.Whether or not new railway lines stopped being built in favour of maglevs，one thing is certain，there is 31，932km of track in the UK，34，449km in France and 4，0726km in Germany，no one is going to convert all of this into maglev track，conventional trains are here to stay for a long time.
New Words and Expressions
guidance［′ɡaidəns］ n. the act of guiding or showing the way 引导，导轨
guideway［′ɡaidwei］ n. track 轨道
viable［′vaiəbl］ adj. sound and workable；feasible 切实可行的；可实施的
embankment［im′bæŋkm（ə）nt；em-］ n. a thick wall of earth that is built to carry a road or railway track over an area of low ground，or to prevent water from a river or the sea from flooding the area 路堤
disruptive［dis′rʌptiv］ adj. causing disorder in sth. 制造混乱的
linear induction motor [电]直线感应电动机；线性感应电动机
Notes
1.In physics，a magnetic field is an entity produced by moving electric charges（electric currents）that exerts a force on other moving charges.（The quantum-mechanical spin of a particle produces magnetic fields and is acted on by them as though it were a current；this accounts for the fields produced by“permanent”ferromagnets.）A magnetic field is a vector field：it associates with every point in space a vector that may vary in time.The direction of the field is the equilibrium direction of a compass needle placed in the field.
2.An electromagnet is a type of magnet in which the magnetic field is produced by a flow of electric current.The magnetic field disappears when the current ceases.
3.A linear motor is essentially an electric motor that has had its stator“unrolled”so that instead of producing a torque（rotation），it produces a linear force along its length.
Many designs have been put forward for linear motors，falling into two major categories，low-acceleration and high-acceleration linear motors.Low-acceleration linear motors are suitable for maglev trains and other ground-based transportation applications.High-acceleration linear motors are normally quite short，and are designed to accelerate an object up to a very high speed and then release the object.They are usually used for studies of hypervelocity collisions，as weapons，or as mass drivers for spacecraft propulsion.
When a linear motor is used to accelerate beams of ions or subatomic particles，it is called a particle accelerator.The design is usually rather different as the particles move close to the speed of light and are usually electrically charged.
Exercises
Ⅰ.Answer the following questions according to the text.
1.What is the principle of a magnet train？
2.What is the dictionary definition of a train？
3.How does the maglev train work？
4.What are the advantages of maglev？
5.What are the disadvantages of maglev？
6.What is the possible solution to the problem？
Why are maglev trains slightly better off than conventional trains in terms of energy consumption？
8.Are maglevs really more environmentally friendly？
9.Will maglevs replace conventional trains？
Choose the best answer to each question.
Ⅱ.Choose the best answer to each question.
1.The dictionary definition of a train is a long line of vehicles travelling in___________ direction.
A.different B.left C.the same D.right
2.A maglev train floats about___________mm above the guideway on a magnetic field.
A.10 B.11 C.9 D.8
3.Because there are no wheels running along there is no wheel___________.
A.maintenance B.noise C.disturbance D.resistance
4.Of the 5，000km that TGV trains serve in France，only about___________km is high speed line.
A.1，000 B.1，100 C.1，200 D.1，300
5.The vast majority of resistive force at high speed is___________resistance.
A.air B.friction C.electricity D.heat
Ⅲ.Translate the following sentences into Chinese.
1.The principal of a magnet train is that floats on a magnetic field and is propelled by a linear induction motor.
2.The second advantage is that because maglev train float，there is no friction.
3.A maglev train floats about 10mm above the guideway on a magnetic field.
4.In terms of energy consumption maglev trains are slightly better off than conventional trains.
5.The fact that a maglev train will not be able to continue beyond its track may seriously hinder its usefulness.
Ⅳ.Summary writing.
In no more than 80 words give an account of this passage.Use your own words as far as possible.