Download Lecture 18

Lecture Eighteen
Physics 100
Fall 2012
 Conservation of Energy
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No Lab Tomorrow.
Lab WILL BE HELD Wednesday, Thursday and
Tuesday of next week.
Second writing assignment due on 12/12/12
Exam 3 discussion
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An electric motor is a device that
converts electrical energy into
mechanical energy.
Electric motors use magnetic force to
cause motion.
Get “mechanical”
energy (motion)
out
Put “electrical” energy
(electricity) in.
Put “mechanical”
energy in to cause
rotation
Get “electrical” energy
(electricity) out
Amount of energy transfered
Power  P 
how long it took for the transfer
( Power ) x(how long you use it)  Amount of energy transfered
Watt x hour or a kilowatt-hour is a unit
of energy which can be converted into a
Joule.
P  iV
Because
V=iR
Kinetic energy (or mechanical
energy) is energy associated with
motion.
 KE=½ mv2 where m is the mass
of an object and v is velocity or
speed
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Put “mechanical”
energy in to cause
rotation
Get “electrical” energy
(electricity) out
 Energy
is not created or
destroyed.
 Rather, energy changes form
(electrical to mechanical for
example).
 Or, is transferred from one
object to another.
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Where did the energy come from to start with?
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Kinetic (mechanical)
Electrical
Heat
Light from the sun and other objects
Sound
Potential (stored): Chemical bonds including
meat and plants, gravitational potential energy,
springs, petroleum