Environmental Engineering Reference
In-Depth Information
of its many forms must be transformed into another in order for stars to shine, planets to
Gravity is perhaps the first type of energy we experience in life. As a baby emerges
from her mother's womb, she experiences for the first time a sense of weightedness.
This force - no doubt disconcerting to a newborn - is truly universal. All bodies in the
universe, from atoms to stars, exert a gravitational attraction on one another. This force is
directly proportional to the mass of the attracting body and indirectly proportional to the
distance from it. That is why astronauts can bounce around on the moon like slow-motion
trampolinists (our satellite has one-fourth the mass of our planet) and why we are drawn to
the Earth rather than the sun (the sun's mass is more than 300,000 times that of the Earth,
but it is 150 million kilometres away).
A falling object, attracted by gravity, exerts another form of energy: kinetic energy. This
can be transferred from one moving object to another, as when a tennis racket strikes a ball.
However, not all the energy is converted in this way. Because the atoms within the tennis
ball are excited and vibrate, they generate heat, or thermal energy. Heat is therefore a form
of kinetic energy, generated at the atomic level.
Heat can be transferred either by the physical impact of particles or in the form of
electromagnetic waves. We are familiar with mechanical waves; by their nature they are
tangible - whether as sound travelling through air, waves in the ocean or ripples in a
pond. Yet electromagnetic waves are an equally constant and natural feature of our world,
in the form of radio waves, microwaves, X-rays, and gamma rays. Light is one such
electromagnetic wave. Heat also radiates, in the form of infrared rays that can be “seen” by
some species of snake through special thermal receptors.
The ancient Greeks found that amber, when rubbed against animal fur, exerted an
attraction on small objects. As a result of this discovery, the Greek term for amber
(
elektron
)formstherootoftheEnglishword'electricity.'Electricitydescribesthepresence
andflowofelectrons, tinynegatively chargedparticles thatorbitthenucleusofeveryatom.
Manifestations of electricity include lightning, static electricity and the flow of electrical
current in a copper wire. Certain elements, particularly metals, easily release and receive
electrons. When we flick a light switch or turn on an appliance, we take advantage of a
flow of electrons jumping from atom to atom along a copper wire, a flow that began, in
most cases, at the nearest power plant.
A chemical reaction occurs when one chemical element 'donates' electrons to another.
The fascination and comfort many of us feel while staring into a campfire may be
attributable to the fact that combustion is humankind's oldest source of external energy. A
