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Chapter 15:
Energy
Energy
• The ability to do work
•Work is a transfer of energy
•Metric unit
Types of
energy
Joule (j)
•Kinetic: moving
•Potential: not moving
Kinetic Energy
The energy of motion
2
mv
Formula: KE = ½
m = mass in kilograms
v = speed in m/s
Potential Energy
The energy that is stored as a
result of position or shape
(not moving)
2 forms: 1. gravitational potential
2. elastic potential
Gravitational Potential Energy
Depends on an object’s height
Energy increases with object’s
height
Formula: PE = mgh
m = mass in kilograms
g = gravitation due to gravity
h = height in meters
Elastic Potential Energy
The stored energy of an
object that is stretched
or compressed
Examples: spring
rubber band
Forms of Energy
Mechanical Energy
Thermal Energy
Chemical Energy
Electrical Energy
Electromagnetic Energy
Nuclear Energy
Mechanical Energy
Energy associated with
motion
Sum of an object’s potential
energy and kinetic energy
Examples: bouncing ball,
speeding train, athletes
Thermal Energy
The energy of all of the
microscopic particles in an
object
Sum of an atoms potential
and kinetic energy
Chemical Energy
The energy that is stored
in chemical bonds
When the bonds are
broken, the released
energy can do work
Examples: Burning wood
Electrical Energy
The energy associated
with electrical charges
Examples: flashlights,
calculator, lightning
Electromagnetic Energy
The energy that travels
through space in waves
Examples: Visible light,
x-rays
Nuclear Energy
The energy stored in an
atom’s nucleus
Most powerful energy
Compare the KE of an 80kg man
and a 30kg boy both moving at
4m/s.
2
KE=1/2 mv
KE = ½ 80Kg(4m/s)2
= 80kg(16m2/s2)
= 1280Kgm2/s2
= ½(1280Kgm2/s2
= 640J
KE = ½ 30Kg(4m/s)2
= 30kg(16m2/s2)
= 480Kgm2/s2
= ½(480Kgm2/s2
= 240J
The man is producing the most KE.
ex. How much PE does a
10kg ball have if its
sitting on a 2m high
shelf?
PE=mgh
Energy Conservation
Energy converted from one
form into another
Examples: wind-up toy, match
Conservation of Energy
Law states: “Energy cannot
be created or destroyed
When energy changes forms,
the total energy remains
unchanged
Energy Conversions
Most common conversion is
between PE to KE
Examples: Pendulums, Pole Vaults
Calculating Energy
Conversion:
(KE + PE)beginning = (KE + PE)end
Practice on Page 458
Energy and Mass
E = mc2
Energy and mass can be
converted into each other
Energy is released as matter
is destroyed, and matter can
be created from energy
Nonrenewable Energy Resources
• Resources that cannot be replaced as
quickly as used.
• AKA  Fossil Fuels
Once living organisms
• ex. Coal, Petroleum (oil), natural gas,
nuclear, etc.
• usually produce pollution
Renewable Energy Resources
• Resources that are replaced as
quickly as used.
• usually environment safe
•Examples include: hydroelectric,
solar, geothermal, wind, and biomass
Hydroelectric Energy
Energy obtained from flowing
water
Kinetic energy is used to turn
turbines and supply
electricity
Advantage: low cost and lack
of pollution
Solar Energy
Sunlight that is converted into
usable energy
Solar energy depends on the
climate
Geothermal Energy
Thermal energy beneath the
Earth’s surface
Not widely available
Other Renewable Resources
Biomass energy – chemical
energy stored in living things
Hydrogen fuel cell – generates
electricity by reacting hydrogen
with oxygen
Conserving Energy Resources
Reduce energy needs and increase
the efficiency of energy use
Energy Conservation – find ways to
use less energy or to use energy
more efficiently
Conserving Energy
• More energy is used in the U.S. than
any other country!
• Why? Money & Lifestyle
• Where does it come from?
93% Nonrenewable resources
7% Renewable resources
Practice test on-line
http://www.proprofs.com/quizschool/quizshow.php?title=EnergyPractice-Test&quesnum=1
http://www.cstephenmurray.com/onlinequizes/physics/workandenergy
/potentialenergyproblems.htm