Download 1.2 Work, Energy, and Power File

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
(Force and distance must be parallel to each other)
W  F d
Joule (j) is the base unit of work
1 joule  1newton 1meter
J  N m
Work Example
A student lifts a 50 pound (lb) ball 4
feet (ft) in 5 seconds (s).
How many joules of work has the
student completed?
Convert English units to SI units
1lb  4.45N
50.0lb  4.45  222.5N  223 N
Solve for Work
1 ft  0.305m
4.00 ft  0.305  1.22m
W  F d
W  222.5N 1.22m
W  271J
Energy
Ability to do work
(light, heat, mechanical, chemical, electrical)
Roller coaster
NASA solar sail
Fuel cell
Forms of Energy
Potential Energy (Stored energy or gravitational energy)
The capacity to do work by virtue of position or
configuration
Forms of Energy
Kinetic Energy (Energy of motion)
Energy which a body possesses because
of its motion, which occurs anywhere from
an atomic level to that of a whole
organism
Energy Transformation
Chemical
Radiant
Electrical
Renewable Energy Sources
Biomass
Hydropower
Wind
Geothermal
Solar
Nonrenewable Energy Sources
Coal
Petroleum
Natural Gas
Uranium
Conservation of Energy
Energy cannot be created or destroyed, but it
can change from one form to another.
Energy Conversion
Changing one form of energy 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
 output 
Efficiency %  
 x100
 input 
Energy Conversion
Examples
Fossil fuels
Solar cells
Wind turbines
Hydroelectric
Nuclear
Chemical → Heat → Mechanical → Electrical
Sunlight → Electrical
Kinetic → Mechanical → Electrical
Gravitational potential → Mechanical → Electrical
Nuclear → Heat → Mechanical → Electrical
Vehicle System Conversion
Chemical
Mechanical
Heat
Which output is desired, mechanical or heat?
What Are Current Energy Concerns?
Consumption
Pollution
Depletion
Dependency
Cost
http://www.eia.doe.gov
What roles do engineers have in energy?
Power
Rate at which work is performed or
energy is expended
W
P=
t
Watt is the base unit of Power
One watt is equal to 1 joule of work
per second
Types of Power
Electrical Power
Uses electrical energy to do work
Mechanical Power
Uses mechanical energy to do work
(linear, rotary)
Fluid Power
Uses energy transferred by liquids
(hydraulic) and gases (pneumatic)
Power Example
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?
Power = Work / Time
Work = 271.45J
271.45 J
P 
5.00 s
J
P  54.3
s
J
1  1 Watt(W )
s
P  54.3 W
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