Mechanical Mechanical

& &

Thermal EnergyThermal Energy

Energy: The ability to do work Energy: The ability to do work or cause change.or cause change.

KineticKinetic Energy: energy of motion (KE = ½ Energy: energy of motion (KE = ½ mvmv22) [m=mass, v=speed]) [m=mass, v=speed]

ex: ½(5kgex: ½(5kg∙2m/s∙2m/s22) )

½(5½(5∙4) ∙4)

½(20½(20) )

10J 10J

[ J = joules][ J = joules]

K.E. is dependent upon K.E. is dependent upon massmass & & velocityvelocity

PotentialPotential Energy: stored up energy Energy: stored up energy (PE = mgh) (PE = mgh)

1. Gravitational P.E. – based on 1. Gravitational P.E. – based on positionposition

2. Elastic P.E. - based on 2. Elastic P.E. - based on conditioncondition 3. Chemical P.E. - based on 3. Chemical P.E. - based on

compositioncomposition. . Energy stored in bonds between Energy stored in bonds between

atoms is chemical energy.atoms is chemical energy.

Law of Conservation of Energy:Law of Conservation of Energy: EnergyEnergy is neither is neither createdcreated nor nor destroyeddestroyed, it is only changed or , it is only changed or transferredtransferred

Energy Conservation examples:Energy Conservation examples: Bouncing ball: Top of the 100 cm drop has 100% GPE

Midway down it has 50% GPE & 50% KE

1 cm from ground it has 99% KE & 1% GPE

When it hits the ground it is 100% EPE, then converts

some to sound & heat energy before bouncing up as KE The food you eat is chemical potential that your body converts

to heat energy your body uses to make you move (KE) A roller coaster converts GPE at top of hill to KE as gravity pulls

it down hill speeding it up; however, gravity slows it down going up hill as KE converts back to GPE. Throughout the journey the roller coaster slows down & converts KE to thermal energy due to friction & air resistance.

Heat: movement of thermal energy Heat: movement of thermal energy from a from a warmerwarmer substance to a substance to a coolercooler substancesubstance

TemperatureTemperature: the measure of the : the measure of the average kinetic energy of particles in average kinetic energy of particles in mattermatter

Kinetic Theory of Matter states that all matter is in constant Kinetic Theory of Matter states that all matter is in constant motionmotion.. (motion stops at Absolute Zero: -273 ºC or -460 ºF)(motion stops at Absolute Zero: -273 ºC or -460 ºF)

The sum of all kinetic energies of all the particles comprising anThe sum of all kinetic energies of all the particles comprising an

object is object is thermalthermal energy. energy. (most matter expands as its thermal energy increases)(most matter expands as its thermal energy increases)

The faster molecules are moving, the more thermal energy they have; The faster molecules are moving, the more thermal energy they have; which is why balls go farther in warm weather than cold.which is why balls go farther in warm weather than cold.

Phase changes of matter (solid, liquid, gas, plasma) are caused by Phase changes of matter (solid, liquid, gas, plasma) are caused by thermalthermal energy transfer, or change in pressure. energy transfer, or change in pressure.

Methods of Heat Transfer:Methods of Heat Transfer: 1.1. ConductionConduction: heat loss by materials in contact with : heat loss by materials in contact with

each other. each other. (occurs in all matter)(occurs in all matter)

1.1. ConvectionConvection heat loss in fluids where heat rises, heat loss in fluids where heat rises, pushing cooler air downward pushing cooler air downward (only occurs in liquids & (only occurs in liquids & gases)gases)

2.2. RadiationRadiation heat loss across a space which requires no heat loss across a space which requires no medium to transfer the heatmedium to transfer the heat

ConductorsConductors are materials that conduct heat are materials that conduct heat well.well.

InsulatorsInsulators are materials that do not conduct are materials that do not conduct

heat well.heat well.

Thermal Thermal EquilibriumEquilibrium: when objects : when objects reach the same temperature as each reach the same temperature as each other.other.

Ex: ice water left on cabinet for 2 hours heats to room temp.Ex: ice water left on cabinet for 2 hours heats to room temp.