Environmental Engineering Reference
In-Depth Information
typicalcombustionreactionseescarbonreactwithoxygen,releasingcarbondioxide(CO
2
),
water (H
2
O), and energy in the form of heat and light.
Every chemical transformation is accompanied by an increase or decrease in energy. In
order to lift a topic from the floor onto a table, we need to expend energy; the muscles
of our arms convert some of the chemical energy we consumed as food into mechanical
energy. To raise the topic even higher onto a bookshelf, we must expend even more energy.
The floor,the table and the bookshelf represent three energetic levels.Ifthe bookfalls from
the shelf, the energy we invested in it will be released in kinetic and thermal energy, as the
molecules in the air and the floor are excited. Because of this, we say that the topic on the
bookshelf has potential energy.
There are numerous ways to store energy. For example, electric energy may be stored
in a battery and kinetic energy behind a dam. The electrons in the battery and the water
molecules behind the dam are 'poised' to release energy. The sum of potential and kinetic
energy is known as mechanical energy. This is the energy associated with the motion or
position of an object. The classic example is a swinging pendulum. The pendulum passes
back and forth between kinetic and potential energy. It attains its maximum kinetic energy
and zero potential energy in the vertical position, because it reaches its greatest speed and
is nearest the Earth at this point. At the extreme positions of its swing, on the other hand, it
will have its least kinetic and greatest potential energy. The energy never leaves the system
but is constantly converted between kinetic and potential. The pendulum slows down and
eventually stops only because a part of the energy is converted into heat through air drag
and friction at the pivot.
1.4 Qualities of Energy
Earthquakes and lightning are among nature's most dramatic shows of force. Little wonder
that so many cultures have constructed myths and legends around these phenomena,
imagining wrathful gods venting displeasure and exacting vengeance. Even without a
divine interpretation, these are awe-inspiring events. The 2011 earthquake that in few
minutes triggered floods and nuclear meltdown in Japan released enough surface energy
to power the city of Los Angeles for a year. A typical lightning bolt releases about one
million megawatts, enough to meet the electricity needs of Germany and France, though
only for a fraction of a second! Yet we are unlikely to tap these immense sources of natural
energy anytime soon. The energy of a lightning bolt is far too concentrated (any conductor
or battery we can currently envisage would be fried to a crisp), and that of an earthquake
far too dispersed to harness. Solar radiation, by stark contrast, strikes the Earth's surface
