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Lecture Eighteen Physics 100 Fall 2012
Conservation of Energy
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
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
how long it took for the transferPower P
( ) (how long you use it) Amount of energy transferedPower x
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
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.
Where did the energy come from to start with?
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