Energy - Wind Energy: Renewable Energy and the Environment - page 15

Natural gas is sold by the mcf (which is 1,000 cubic feet) and it has an energy content of around
10 6 BTU. You need to be careful when comparing energy from coal with other sources, because
1 metric ton 1,000 kg 2,200 lb, 1 ton or long ton 2,400 lb, and 1 short ton 2,000 lb. Metric tons
will be used unless noted. Also, different types of coal have different energy contents. A barrel of oil
(160 L, 42 gallons) is refined to around 166 L (44 gallons) of components, of which 72 L (19 gallons)
is gasoline.
Objects in motion can do work; therefore, they possess energy, kinetic energy (KE):

KE 0.5 mv 2 (2.2)

where m is the mass of the object and v is its speed.

EXAMPLE 2.1
A car with a mass of 1,000 kg moving at 15 m/s has kinetic energy.

KE 0.5 * 1,000 * 15 * 15 112,500 J 1.1 * 10 5 J to two significant figures

Because objects interact, for example, by gravity or electromagnetics, then due to their rela-
tive position they can do work or have energy, potential energy (PE). To raise a 1 kg mass, 2 m
high, requires 20 J of energy. Then at that upper level, the object has 20 J of potential energy.
Energy from fossil fuels is chemical energy, which is the potential energy due to the electromag-
netic interaction.
Power is the rate of energy use or production and is equal to energy divided by time.

P E / t , watt J/s (2.3)

If either power or energy is known, then the other quantity can be calculated for any time period.
Always remember, a kilowatt (kW) is a measure of power and a kilowatt-hour (kWh) is a measure
of energy.

E P * t (2.4)

EXAMPLE 2.2
A 5 kW electric motor that runs for 2 h consumes 10 kWh of energy.

EXAMPLE 2.3

Ten 100-watt lightbulbs that are left on all day will consume 24 kWh of energy.

Heat is another form of energy, thermal energy. Heat is just the internal kinetic energy (random
motion of the atoms) of a body. Rub your hands together and they get warmer. As you heat your
home, you are increasing the speed of the particles of air and other materials in the home. Heat and
temperature are different. Heat is energy, and temperature is the potential for transfer of heat from
a hot place to a cold place. Do not equate temperature to heat (energy).

2.3 FUNDAMENTALS CONCERNING ENERGY
A major unifying concept is energy and how energy is transferred. The area of physics that deals
with heat is called thermodynamics. Part of today's understanding of energy can be embodied in the
following laws or principles of thermodynamics:

1. Energy is conserved. Energy is not created or destroyed, only transformed from one form
to another. In laymen's terms, this means that all you can do is break even. A number of
patents have been issued for a perpetual motion machine [1], a device that produces more