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