Page 44 - Alternative Energy Systems in Building Design

THE CONCEPT OF ENERGY IN VARIOUS SCIENTIFIC FIELDS 21

energy converts into elastic potential energy. On bouncing back up, this potential energy
once again becomes kinetic energy. The two forms, though seemingly very different,
play important roles in complementing each other.

GRAVITATIONAL POTENTIAL ENERGY
The gravitational force near the earth’s surface is equal to the mass m multiplied by
2
the gravitational acceleration g and is 9.81 m/s .

TEMPERATURE
On the macroscopic scale, temperature is a unique physical property that determines
the direction of heat flow between two objects placed in thermal contact. If no heat
flow occurs, the two objects have the same temperature because heat flows from the
hotter object to the colder object. These two basic principles are stated in the zeroth
law of thermodynamics and the second law of thermodynamics, respectively. For a
solid, these microscopic motions are principally the vibrations of its atoms about their
sites in the solid.
In most of the world (except for the United States, Jamaica, and a few other countries),
the degree Celsius scale is used for most temperature-measuring purposes. The global
scientific community, with the United States included, measures temperature using the
Celsius scale and thermodynamic temperature using the scale in Kelvin scale, in
which 0 K =−273.15°C, or absolute zero.

SPECIFIC HEAT CAPACITY
Specific heat capacity, also known as specific heat, is a measure of the energy that is
needed to raise the temperature of a quantity of a substance by a certain amount.

CHEMICAL ENERGY
Chemical energy is defined as the work done by electrical forces during the rearrange-
ment of electric charges, electrons, and protons in the process of aggregation. If the
chemical energy of a system decreases during a chemical reaction, it is transferred to
the surroundings in some form of energy (often heat). On the other hand, if the chemi-
cal energy of a system increases as a result of a chemical reaction, it is from the
conversion of another form of energy from its surroundings. Moles are the typical
units used to describe change in chemical energy, and values can range from tens to
hundreds of kilojoules per mole.

RADIANT ENERGY
Radiant energy is the energy of electromagnetic waves or sometimes of other forms of
radiation. As with all forms of energy, its unit is the joule. The term radiation is used
especially when radiation is emitted by a source into the surrounding environment.