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Pages 300-309
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Energy – the ability to cause change
 Work is accomplished when a force causes an
object to move in the direction of the force
▪ Work = force x distance

Measured in joules (J)
 Named after James Prescott Joule
▪ English Scientist who work to improve electric motors.
Study heat and it relationship to work. Paved the way
for the theory of the conservation of energy

Takes many different forms and has many
different effects
 Ex: Your body uses energy provided by the food
you eat and converts it to other forms

The two types of energy are called kinetic
energy and potential energy


Kinetic Energy is the energy of motion
The amount of KE that an object has depends
on two things: mass and speed(KE = ½ m*s*s)
 Speed has a greater impact = (KE=mv2/2)
 Ex: a car and a bike are both moving at the same
speed  the car has more mass so it has more KE
 Ex: A cheetah has more KE when it is running than
it does when it is walking or sitting under a tree
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Potential Energy is the stored energy that an
object has due to its position
One type of PE is called gravitational PE 
depends on the mass and height of object
(GPE = m*9.8*h OR GPE = w * h)
 Ex: A skydiver has more GPE on the plane than
she does after she jumps out and gets closer to
the ground
 Ex: A heavy book has more GPE than a lighter
book when they are sitting on the same shelf
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
KE is the energy of motion, but PE is stored
energy that can be converted into motion
Many objects can have both KE and PE
 Ex: an object can be both moving and above
ground
▪ If you are walking (KE), you still may trip and fall (PE)

Mechanical energy is the KE plus the PE due
to position (ME = KE+PE)
 Ex: A skate boarder on a half-pipe has both KE
and PE. At the very bottom of the half-pipe, his
KE is greatest and his PE is lowest. At the top of
the half-pipe, his PE is greatest and his KE is
lowest.
 Ex: Roller Coaster sheet

The Law of Conservation of Energy states
that energy can neither be created nor
destroyed  It can only be transformed!
 Ex: When I pick up a book, I am using my KE to
increase the book’s GPE
 Gravitational
 Electricity
 Nuclear
 Motion
 Mechanical
 Radiant (light)
 Chemical
 Sound
 Thermal