First Principles - Sustainable Design: The Science of Sustainability and Green Engineering - page 47

Matter is anything that has both mass and volume. Matter is found in three
basic phases : solids, liquids, and gases. The phases are very important for envi-
ronmental science and engineering. The same substance in one phase may be
relatively “safe,” but in another phase, very hazardous. For example, a highly
toxic compound may be much more manageable in the solid and liquid phases
than it is in the gas phases, particularly if the most dangerous route of exposure
is via inhalation. Within the same phase, solid and liquid aerosols are more of a
problem when they are very small than when they are large because larger parti-
cles settle out earlier than do lighter particles, and small particles may penetrate
airways more efficiently than do coarse particles.
Mass and Work
We have been using the term mass but have yet to define it formally. Mass is the
property of matter that is an expression of matter's inertia (recall Newton's first
law). So now we can also define energy. The capacity of a mass to do work is
known as the energy of the mass. This energy may be stored or it may be released.
The energy may be mechanical, electrical, thermal, nuclear, or magnetic. The
first four types have obvious importance to green engineering. The movement of
fluids as they carry pollutants is an example of mechanical energy . Electrical energy is
applied in many treatment technologies, such as electrostatic precipitation, which
changes the charge of particles in stack gases so that they may be collected rather
than being released to the atmosphere. Thermal energy is important for heating
and cooling systems, waste incineration, and sludge treatment processes. Nuclear
energy is converted to heat that is used to form steam and turn a turbine, by
which mechanical energy is converted to electrical energy. The environmental
problems and challenges associated with these energy conversions include heat
transfer, release of radiation, and long half-lives of certain isotopes that are formed
from fission. Even the fifth form, magnetic energy , has importance to environmental
measurements in its application to gauges and meters.
Energy is a scalar quantity. That is, it is quantified by a single magnitude. As
mentioned, this contrasts with a vector quantity, which has both magnitude and
direction, and which we discuss in some detail shortly. Although energy is a
positive scalar quantity, a change in energy may be either positive or negative. A
body's total energy can be ascertained from its mass m and its specific energy (i.e.,
the amount of energy per unit mass). The law of conservation of energy states that
energy cannot be created or destroyed, but it may be converted among its different
forms. So, in the environment, we often see the conversion of mechanical energy
into electrical energy (e.g., a turbine), some of which in turn is converted to heat
(hence, the need for cooling before makeup water from a turbine). The key of