Transcript 4.2 Conservation of Energy

Conservation of Energy
Section 4.2
Pictures from
http://www.glenbrook.k12.il.us/gbssci/
phys/Class/energy/u5l1b.html
Changing Forms of Energy

Many devices convert energy from one form
to another
– Electrical to thermal
– Mechanical to Electrical

In Vehicles:
– Engine: Chemical Energy to Kinetic energy
– Spark plug: Electrical Energy converts gasoline’s
chemical energy to thermal energy
– Thermal Energy causes gases to expand
– Expanding is mechanical energy, which moves
parts of the car = kinetic energy
Conversions Between Forms of
Energy

Plants: light into chemical
– Uses E from sunlight to make bonds

Mechanical energy – total KE and PE in a
system
– ME = KE + PEG + PEe

Amount of ME is due to:
– Position and Motion

Can PE be converted into KE?
Falling Skater

When an object falls
– Before release: All E is PE
– As it falls, PE is converted to KE
– At the bottom of the fall, all is KE
ME remains the same
 See pg 109 for baseball
 See next slide for swing

Law of Conservation of Energy

Energy cannot be created or destroyed.
– E is constant in universe
– Can only be transformed from one type to
another
Energy can be transformed into non-useful
forms, like heat
 “Disappearing energy” – doesn’t disappear

– Is converted into thermal energy by friction
Energy

Energy in sun- from transformation of
mass into energy
– Fusion: 2 H nuclei  helium nucleus +
neutron + energy

Nuclear Power Plants- Energy from fissionbreak apart nuclei
– In fission and fusion, mass and energy
TOGETHER are conserved
– Fission: uranium + neutron  Xe + Sr +
neutrons + energy
Energy in You
Kinetic energy:
 Thermal energy:
 Chemical energy:
 Electrical energy:
