energy, work, and power · power power is the rate at which work is performed or energy is...
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Work, Energy, and Power
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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
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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
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Energy
Definition: The ability to do work.
(light, heat, mechanical, chemical, electrical)
NASA solar sail Fuel cell Roller coaster
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Forms of Energy - Potential Energy
Stored or gravitational energy. The capacity to do
work by virtue of position or configuration.
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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.
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Energy Transformation
The conversion of one form of energy into
another form.
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Energy Transformation
Chemical
Radiant
Electrical
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Renewable Energy Sources
Biomass Hydropower Geothermal
Wind Solar
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Nonrenewable Energy Sources
Petroleum
Natural Gas Coal
Uranium
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Conservation of Energy:
Energy cannot be created or destroyed, but
it can change from one form to another.
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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.
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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?
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What Are Current Energy Concerns?
Consumption
What roles do engineers have in energy?
Pollution
Depletion
Dependency
Cost
http://www.eia.doe.gov
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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).
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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).
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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?
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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