Work, Energy, and Power
Work, Energy, and Power
Work (W) The product of the force (F) applied to an
object over a distance (d) in which the object
travels as a result of the force.
W F d
The Joule (j) is the metric unit of work.
1 1 1joule newton meter
J N m
A student lifts a 50 pound (lb) ball 4
feet (ft) in 5 seconds (s).
How many joules of work has the
student completed?
W F d
222.5 1.22W N m
271W J
1 4.45lb N
Convert English units to SI units
1 0.305ft m
Solve for Work
Work Example
50.0 4.45 222.5 223 lb N N 4.00 0.305 1.22ft m
Energy
Definition: The ability to do work.
(light, heat, mechanical, chemical, electrical)
NASA solar sail Fuel cell Roller coaster
Forms of Energy - Potential Energy
Stored or gravitational energy. The capacity to do
work by virtue of position or configuration.
Forms of Energy - Kinetic Energy
The energy of motion. The energy a body
possesses because of its motion, which
occurs anywhere from an atomic level to
that of a whole organism.
Energy Transformation
The conversion of one form of energy into
another form.
Energy Transformation
Chemical
Radiant
Electrical
Renewable Energy Sources
Biomass Hydropower Geothermal
Wind Solar
Nonrenewable Energy Sources
Petroleum
Natural Gas Coal
Uranium
Conservation of Energy:
Energy cannot be created or destroyed, but
it can change from one form to another.
Energy Efficiency: The ratio of the useful
energy delivered by a dynamic system to the
energy supplied to it.
Entropy: The loss of energy during conversion.
outputEfficiency % x100
input
Energy Conversion:
Changing one form of energy to another.
Energy Conversion
Examples
Fossil fuels Chemical → Heat → Mechanical → Electrical
Solar cells Sunlight → Electrical
Wind turbines Kinetic → Mechanical → Electrical
Hydroelectric Gravitational potential → Mechanical → Electrical
Nuclear Nuclear → Heat → Mechanical → Electrical
Vehicle System Conversion
Chemical
Mechanical Heat
Which output is desired, mechanical or heat?
What Are Current Energy Concerns?
Consumption
What roles do engineers have in energy?
Pollution
Depletion
Dependency
Cost
http://www.eia.doe.gov
Power
Power is the rate at which work is
performed or energy is expended.
WP=
t
The watt is the base unit of power.
One watt is equal to 1 joule of work per
second.
Power is also measured in horsepower (HP).
Types of Power
Electrical Power:
Uses electrical energy to do work.
Mechanical Power:
Uses mechanical energy to do work (linear,
and rotary forms).
Fluid Power:
Uses energy transferred by liquids
(hydraulic) and gases (pneumatic).
Power Example
Power = Work / Time
Work = 271.45J
P
P
271.45 J
5.00 s
J54.3
s
P
J1 1Watt(W)s
54.3 W
A student lifts a 50.0 pound (lb) ball 4.00 feet (ft) in 5
.00seconds (s).
How many watts of power are used to lift the ball?
Resources
McGraw-Hill dictionary of engineering. (2nd ed.). New York, NY: McGraw-Hill.
Microsoft, Inc. (2008). Clip art. Retrieved January 10, 2008, from http://office.microsoft.com/en-us/clipart/default.aspx
National Aeronautics and Space Administration (NASA). (1997). Daedalus. Retrieved April 2, 2008, from http://www.dfrc.nasa.gov/Gallery /Photo/Daedalus/
U.S. Department of Energy. (2008). Scientific forms of energy. Retrieved March 23, 2008, from http://www.eia.doe.gov/kids/energyfacts/science/formsof
energy.html