Unit 5 – Lecture 2

Review: PE & KEPotential Energy – “stored” E Kinetic Energy – energy of motion /

“released” E

Conservation of EnergyLaw of Conservation of Energy:

energy can neither becreated nor destroyed in normal reactions

energy can be changed in form from one to another

initial energy = final energyenergy in = energy outaka 1st law of thermodynamics

Mechanical EnergyMechanical E – total amount of PE & KE in a

systemas PE decreases, KE increasesas PE increases, KE decreaseswhat kind of relationship is this…direct or

inverse?

Mechanical EnergyEquation:MEinitial = MEfinal

(PE + KE)initial = (PE + KE)final (m g h + ½ m v2 )initial = (m g h + ½ m v2 )final

Mechanical EnergyME in a pendulum:

PracticeAt 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 changeAbility to increase energy Ability to decrease

work

Joules is NOT a unit for which of these?PE KEForce Work

Forms of EnergyMechanical Energy

energy of an object due to its motion [kinetic E] or position [potential E]

Forms of EnergyElectromagnetic E

waves of mostly invisible E

light energy often is converted into thermal E

can be converted into chemical E through photosynthesis

Forms of EnergyChemical E

stored and released in the bonds between atoms

food, batteries

Forms of EnergyNuclear E

stored and released from the nucleus of an atom

Forms of EnergyThermal E

heat in all its forms and flows

recall – exothermic & endothermic

transferred through conduction, convection, & radiation

Forms of EnergyElectrical 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]

PracticeWhen 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?