## Thursday, September 15, 2005

### What Are MagLev Trains?

Engineers and scientists not only invent new modes of transportation, but they also look for ways to make existing vehicles faster, safer, quieter, and more energy-efficient (i.e. make them use less energy).

One area of current research is the MagLev train. MagLev stands for Magnetic Levitation. Demonstration MagLev trains have already been built in Germany and Japan, where they have reached maximum speeds of 250 to 350 mph!

This is still not as fast as commuter airplanes fly (~550 mph), but it is still a huge improvement over conventional trains, which travel at about 80 mph. So, you can see that a trip on a MagLev train would be about 3 to 4 times as fast as the same trip on a regular train! This is because MagLev trains don't touch the tracks, so only air resistance slows them down (vs. the large amount of friction between the tracks and wheels of a regular train). This also makes MagLev trains much quieter than regular trains.

Now, let's look at how MagLev trains work. Every magnet has two opposite sides: north and south. If you've ever played with magnets, then you know that opposites attract and likes repel. In other words, north and south attract, while two norths or two souths will push away from each other.

Imagine that you have one large flat magnet laying on a table so that its north side is facing the ceiling and its south side is flat against the table top. If you put a smaller magnet on top of the larger magnet so that their north sides touch, what will happen? The two magnets will repel each other. If this force is strong enough and if the small magnet is light enough, then the small magnet will levitate (float) above the larger one.

MagLev trains use the principle that we just discussed, but on a much larger scale. Most MagLev train designs rely on repulsion between magnets on the tracks and magnets on the bottom of the train.

In our tabletop example above, we got the small magnet to levitate but not to move forward. Thus, a power supply is needed to change the magnetic forces behind and in front of the train in such a way that the train is pushed and pulled forward.

How are the power supply and the magnets related? Unlike permanent magnets (e.g. kitchen magnets), the magnets used for MagLev trains are electromagnets (their magnetic forces are created by electricity). Since these electromagnetic forces rely on a power supply, their strength and direction can be changed by altering the power supply.

Current research is focused on making this power supply more energy-efficient, and thus cheaper to maintain. Once the price of operating the train is reduced, MagLev train tickets could be sold at reasonable prices to the general public.

### Little Lion Experiment:

As objects move further apart, the magnetic attraction or repulsion between them gets weaker. To observe this relationship, obtain a few different strong refrigerator magnets. Tie a piece of string (about 8" long) onto a small metal paper clip. Then, tape the free end of the string onto the table.

Hold one refrigerator magnet next to the paper clip then raise the magnet until the string is pointing straight up. Slowly pull the magnet upwards one millimeter off of the paperclip. If the paperclip drops, then the magnet is fairly weak. If the paperclip stays suspended, then the magnetic attraction is still strong enough to fight the forces (mostly gravity, but also the tension in the string) pulling the clip downwards.

Continue moving the magnet upwards. Eventually, the paperclip will drop. This is when the magnetic force pulling it upwards becomes less than the forces of gravity and tension pulling it downwards.

These downward forces depend on the string and the paperclip, so they are the same no matter which magnet is used. So, if you use the same paperclip and string each time, then the distance at which the paperclip drops depends only on the strength of the magnet.