Agriculture Reference
In-Depth Information
a proper explanation of why one's designs are green. That is, we not only want
to offer green designs but also to give reasons for their being green. Throughout
the topic, when a technique or guide is given, it is accompanied by a scientific
explanation of how it works. In particular, two sets of first principles must form
the basis of all sustainable designs: the laws of thermodynamics and motion.
Physics
Physics concerns itself with matter, energy, motion, and force. Arguably, all other
sciences are simply branches of physics. Even chemistry, which is the science
that deals with the composition, properties, transformations, and forms of mat-
ter, is merely a discipline within physics. Therefore, we will not draw “bright
lines” between physics and chemistry. Often, in this topic and elsewhere, the
dichotomy is avoided by using the term physicochemical to address properties and
characteristics that are included in both physics and chemistry. Therefore, force,
velocity, flow rates, discharge, and friction are clearly terms of physics. Simi-
larly, redox, acidity-alkalinity, stoichiometry, and chirality are terms of chemistry.
However, kinetics, sorption, solubility, vapor pressure, and fugacity are phys-
iochemical terms. In green engineering and sustainable design, we are clearly
concerned with how underlying principles of thermodynamics and motion af-
fect our projects.
Thermodynamics
Thermodynamics is the science of heat (Greek: therme = heat; dynamis = power).
In particular, it addresses changes in temperature, pressure, and volume in macro-
scopic physical systems. Heat is the transfer of thermal energy between bodies that
are at different temperatures. In the process of such transfer, movement occurs.
For example, heat transfer leads to the turning of the wheels of an automibile,
or the movement of air through a building. We discuss motion as a separate
scientific underpinning of design. However, it is important to keep in mind that
thermodynamics is concerned with the transformation of heat into mechanical
work and of mechanical work into heat.
The principles of potentiality link thermodynamics and mechanics (and hence
green engineering's concern with efficiencies of motion). That is, thermody-
namics is concerned with the flow of heat from a hotter body to a colder body.
Other potentials important to green engineering include elevation (flow from
higher elevation to lower elevation, i.e., the engineering concept of head ), and
electricity (voltage difference between two points, toward the ground, where
voltage
=
0). These differentials make for motion. Water flows downhill, charge
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