Transcript Energy Cont`d - Fulton County Schools

Unit 5 – Lecture 2
Review: PE & KE
 Potential Energy – “stored” E
 Kinetic Energy – energy of motion / “released” E
Conservation of Energy
 Law of Conservation of Energy:
 energy can neither be
created nor destroyed in
normal reactions
 energy can be changed in
form from one to another
 initial energy = final energy
 energy in = energy out
 aka 1st law of thermodynamics
Mechanical Energy
 Mechanical E – total amount of PE & KE in a system
 as PE decreases, KE increases
 as PE increases, KE decreases
 what kind of relationship is this…direct or inverse?
Mechanical Energy
Equation:
 MEinitial = MEfinal
 (PE + KE)initial = (PE + KE)final
 (m g h + ½ m v2 )initial = (m g h + ½ m v2 )final
Mechanical Energy
 ME in a pendulum:
Practice
At which point…
 is GPE at a maximum?
 why?
 is KE at a maximum?
 why?
Practice
Which of these describes E? [any]
 Ability to do work
Ability to cause change
 Ability to increase energy
Ability to decrease work
Joules is NOT a unit for which of these?
 PE
KE
 Force
Work
Forms of Energy
 Mechanical Energy
 energy of an object due to
its motion [kinetic E] or position [potential E]
Forms of Energy
 Electromagnetic E
 waves of mostly invisible E
 light energy often
is converted into thermal E
 can be converted into
chemical E through
photosynthesis
Forms of Energy
 Chemical E
 stored and released in the bonds between atoms
 food, batteries
Forms of Energy
 Nuclear E
 stored and released from the nucleus of an atom
Forms of Energy
 Thermal E
 heat in all its
forms and flows
 recall –
exothermic
& endothermic
 transferred
through
conduction,
convection, &
radiation
Forms of Energy
 Electrical E
 separation and movement of electrons
 [not really a form of E
on its own – it is a
combination of forms
of Mechanical and
Electromagnetic E]
Practice
 When you are watching tv, what energy conversions
are taking place?
 Which energy transformation takes place when a
match is struck against the side of a matchbox and
bursts into flames?
 What causes you to hear something? What kind of
energy is sound?