Glossary
Topic 7 Foundation Engineering “A”
Peter,
glossary …………….
Work Required:
The work required or sometimes the work done is the amount of energy needed to
move an external force through a distance. The direction in question is the
direction of motion. Work is energy being transferred to/from an object when it is
acted on by an unbalanced force and has units of (J). Work is not an energy
storage term it represents an exchange of energy.
Kinetic Energy:
Kinetic energy is energy stored in an object by virtue of its motion. It is directly
proportional to the product of the bodies mass and its velocity squared. Any work
done to change a body’s velocity is stored as an increase or decrease in kinetic
energy – kinetic energy has units of (J).
Potential Energy:
Potential energy is energy stored in an object by virtue of its position in the Earth’s
gravitational field. It is directly proportional to the product of the bodies mass and
its elevation with respect to some datum point. Any work done to change a body’s
elevation in the Earth’s gravitational field is stored as an increase or decrease in
potential energy – potential energy has units of (J).
Heat:
Heat is energy that is transferred to or from an object when there is a temperature
difference between the object and its surroundings. It is an energy transfer term
and has units of (J).
Internal Energy:
Internal energy is energy a body has by virtue of the total kinetic and potential
energy of all the atoms or molecules the make up the body. Internal energy
depends on the temperature and pressure of a substance. The units for specific
internal energy is (J kg-1) and for total internal energy (J).
Energy Conservation Principle:
The energy conservation principle states: “Energy cannot be created or destroyed,
it can only be changed from one form to another”
Chemical Energy:
Chemical energy is energy absorbed or released when chemical bonds are made
or broken. Chemical energy is only evident if a chemical reaction takes place and
then it will be noted that the reacting system will either absorb or release heat.
Chemical energy is an energy storage term and has units of (J).
Nuclear Energy:
Nuclear energy is energy associated with binding together the nucleus of an atom.
This type of energy is only evident if a nuclear reaction takes place. Nuclear
energy is an energy storage term and has units of (J).
Electromagnetic Energy:
Is energy associated electromagnetic waves. There is a spectrum of
electromagnetic waves of different wavelengths. Engineers commonly deal with
thermal radiation which is radiation in the infra-red part of the spectrum. Heat is
transferred as thermal radiation from a hotter to a cooler object. Electromagnetic
energy may be transferred through a vacuum. This is an energy transfer term and
has units of (J).
Sound Energy
Sound energy is an energy transfer term and is caused by energy being
transferred from a vibrating system. Sound is transferred through a solid, liquid or
gas but cannot be transferred through a vacuum.
Renewable Energy
Renewable energy is energy that comes from any source that come be
replenished, e.g. wind, sunlight, tides, waves, hydroelectric, biomass, biofuels and
geothermal.
Power:
Power is the rate at which energy is produced or consumed; it is energy per unit
time. The unit of power is the watt (W) and is defined as 1 W = I J s -1.
Thermal Power
Thermal power is also known as the rate of heat transfer. It is the amount of heat
(J) transferred per second and has units of (J s-1) or (W).
Mechanical Power:
Mechanical power is the power transferred from or to a rotating shaft. It is the
product of the torque (N m) time the angular velocity (s-1) of the shaft. As such
mechanical power has units of (J s-1) or (W).
Efficiency:
The efficiency with which a device converts energy from one form into another is
the ratio of the output power divided by the input power. The difference between
input power and output per is equal to the energy losses, each second, between
the input of the device and the output.
Kilowatt-hours:
Kilowatt-hours (kWh) is the product of power times time. If power is energy per
unit time, then power times time must be energy. Thus kilowatt-hours is an
amount of energy generated or consumed.
P.S. Peter…….may not have highlighted “Mechanical Power” – if not please add it to the
list and tag it in the text. Hopefully you will find and example in the “Mechanical
Power” section.