This is a great question! There are actually
quite a few kinds of trains, and each kind has a
different method of propulsion (moving forward).
The first trains were powered by steam locomotive
engines. Essentially, a steam engine works by
taking advantage of the fact that when liquid
water boils and becomes gas, it expands.
engine consists of a boiler, which carries water
and is attached to a cylinder and piston. The
water in the boiler is heated, either with wood or
coal, and as the water boils, steam is funneled
into the cylinder, which causes the piston to move
back and forth. The piston in turn is
a machine that moves the wheels of the train!
These days, however, there are lots of ways to
power trains. Electricity can be used to power
train motion, like the cable cars you can find in
San Francisco. There are also trains that take
advantage of gravity to move forward, and some
work by taking advantage of differences in air
Maglev (magnetic levitation) is another
method for propelling trains forward and is often
used for monorail trains, which can be found in
many big cities all over the world. In this
technology, magnets are used to levitate ("push up
on") the train so it hovers above the rail. A
large electric coil which generates a magnetic
field is used to propel the train forward using an
alternating current. I hope this helps!
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