ENERGY AND POWER

THERMODYNAMICS

MOMENTUM

MOMENTUM P = mv

FORCE F = ma = mv/t

IMPULSE Ft = mv = P (Momentum)

MOMENTUM IS ALWAYS CONSERVEDThere has been the same amount of Momentum in the Universe since the Big Bang. Momentum lost in a collisionGoes into heat, which is increased momentum of the individualMolecules within the heated object.

ENERGY

KINETIC ENERGY (energy at work)

KE = 1/2 M V2 W = F x d

POTENTIAL ENERGY (available for work)

ENERGY IS THE ABILITY TO DO WORK.WORK IS THE APPLICATION OF A FORCE OVER A DISTANCE: IT IS ENERGY USED UP

TOTAL ENERGY=KE + PE = CONSTANT

FORMS OF ENERGY

POTENTIALKINETIC

All the rest are versions of the aboveHEAT (CAN BE MECHANICAL)CHEMICALLIGHTELECTRICALNUCLEAR

WORK

WORK IS FORCE OVER A DISTANCE

NEWTON-METREJOULE

POWERPOWER IS A MEASURE OF HOW FAST WORK CAN BE DONE P = W/t

POWER IS MEASURED IN WATTSWORK PER UNIT TIME

JOULES/SECONDFORCE TIMES SPEED (FxV)

NEWTON-METER PER SECOND

P = W/t = Fd/t = Fv

CONSERVATION OF ENERGY

ENERGY IS MANIFEST IN MANY FORMS, BUT ALTHOUGH WE CAN CONVERT ENERGY FROM ONE FORM TO THE OTHER, IN A CLOSED SYSTEM, THE TOTAL ENERGYREMAINS A CONSTANT.

ENERGY CAN NEITHER BE CREATEDNOR DESTROYED

ENERGY

IF POWER IS STRENGTH, ENERGY IS ENDURANCE

ENERGY is POWER X TIME E = Pt = Fdt/t = Fd = WORK

UNIT OF ENERGY =WATT-SECOND=JOULE=NEWTON-METER

HEAT TRANSFER

CONDUCTION

CONVECTION

RADIATION

EVAPORATION

STEPHAN-BOLTZMANN LAW

E(radiation) = a constant x T4

KIRCHHOFF’S LAW: GOOD ABSORBERS ARE ALSO GOOD EMITTERS

BLACK BODY = A PERFECT EMITTER

WIEN’S LAW

Lamda (max) = C/T

The peak wavelength of the emitted radiation is

inversely proportional to the absolute temperature

INVERSE SQUARE LAW

Intensity = Io/d2

100

50

1 2 3 4 5 6

*

** * * *

1- 1002- 25 = 1/43- 11.1= 1/94- 6.25= 1/165- 4 = 1/256- 2.78 = 1/36

Radiation decreases by the square of the distance

NUCLEAR ENERGY

E = MC2

FISSION: BREAKING A NUCLEUS APART

FUSION: FORCING TWO NUCEII TOGETHER

HEAT

• One calorie is the amount of heat to raise one gram of water, one degree Celsius.

• Specific Heat: Each material needs a certain amount of heat to raise its temp one degree; usually less than one calorie.

• One calorie is equivalent to 4.19 joules, enough energy to raise one gram of matter 428 metres higher.

THERMAL EXPANSION

• Heat causes the atoms or molecules of any material to “jiggle”.

• When jiggling they need more room, so the volume increases with temperature (normally).

• Water is an exception: with the temp going down between 4 deg and 0 degrees, water will expand, and on freezing will increase volume by 9%.

• Ice has a density of 0.92; thus it floats.• The lowest levels of a pond freeze last, if at all.

CHANGES OF STATE

• EVAPORATION

• CONDENSATION

• BOILING – HEAT OF VAPORIZATION

540 CALORIES

CHANGES OF STATE

• MELTING

• FREEZING –

• HEAT OF FUSION 80 CALORIES

• SUBLIMATION

THERMODYNAMICS

• HEAT FLOWING IS THERMAL ENERGY

• WORK CAN PRODUCE HEAT –

• HEAT CAN PRODUCE WORK

THERMODYNAMICS

FIRST LAW: ENERGY IS CONSTANTE1-E2=HEAT INPUT - WORK DONE(You can’t win)

SECOND LAW: HEAT FLOWS FROM HOT TO COOLER(You can’t break even)

ENTROPY ALWAYS INCREASESEVERYTHING TENDS TO GET MORE DISORDERED(You can’t get out of the game!)

THIRD LAW: AT ABSOLUTE ZERO, ALL MOTION CEASES

THERMODYNAMICS

• FIRST LAW:

• TOTAL HEAT = CHANGE IN INTERNAL ENERGY + WORK OUTPUT

• CHANGE IN ENERGY = HEAT IN – WORK DONE

THERMODYNAMICS

• SECOND LAW

• HEAT FLOWS FROM HOT TO COOLER

• EFFICIENCY IS WORK/HEAT INPUT

• PERFECT EFF. = (Thot –Tcold)

Thot

ENTROPY

• SECOND LAW:

• ENTROPY ALWAYS INCREASES

• ENTROPY IS A MEASURE OF DISORDER

THERMODYNAMICS

• THIRD LAW:

• AT ABSOLUTE ZERO ALL ORDER AND MOTION CEASE