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ENERGY
Chapters 4 and 6
Energy
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Energy is the ability to cause change.
Energy is the ability to do work - exert
force over distance to move object.
The units for Energy are the Joule (J)
and the Calorie (cal).
There are many forms
of Energy
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Kinetic
Potential
Thermal
Electrical
Chemical
Nuclear
Kinetic Energy (KE)
Energy in MOTION!
 Depends on mass +
speed
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Potential Energy (PE)
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Stored energy
Depends on positions and conditions of the
objects before they move
Forms of Potential
Energy
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Elastic
 Rubber band
Chemical
 Bonds
Electrical
 Position of
charges relative
to each other
Nuclear
 Nucleus
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Magnetic
Gravitational (GPE)
 Position above
Earth’s surface
 Depends on mass
+ height above
ground
 Compare objects
on shelf
Kinetic Energy Calculations
KE = ½ mv2
 KE = Kinetic Energy in Joules
 m = mass
 v = velocity
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Kinetic Energy Calculations
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A jogger whose mass is 60 kg is moving
at a speed of 3 m/s. What is the
jogger’s kinetic energy?
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KE = ½ mv2
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KE=(.5)(60)(9) = 270 J
Kinetic Energy Calculations
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What is the kinetic energy of a baseball
moving at a speed of 60 m/s if the
baseball has a mass of 0.15 kg?
KE = ½ mv2
 KE = (.5)(.15)(3600) = 270 J
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Gravitational Potential Energy
Calculations
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GPE = mgh
GPE = gravitational potential energy (J)
m = mass (kg)
g = 9.8 m/s2
h = height (m)
GPE Calculations
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What is the gravitational potential
energy of a ceiling fan that has a mass
of 7 kg and is 4 m above the ground?
GPE = mgh
GPE= (7)(9.8)(4) = 274.4 J
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GPE Calculations
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Find the height of a baseball with a mass
of 0.15 kg that has a gPE of 100 J?
GPE = mgh
100 = (.15)(9.8)(h)
100=1.47h
Divide each side by 1.47
h=68.03 m
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GPE Calculations
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Find the GPE of a coffee mug with a mass
of 0.5 kg on a 1.2 m high counter top.
GPE = mgh
Energy Transformations in
Swing
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Highest KE?
Lowest KE?
Highest PE?
Lowest PE?
When does
KE = 0?