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### ENERGY AND POWER

THERMODYNAMICS

MOMENTUM

MOMENTUM P = mv

FORCE F = ma = mv/t

IMPULSE Ft = mv = P (Momentum)

MOMENTUM IS ALWAYS CONSERVED

There has been the same amount of Momentum in the

Universe since the Big Bang. Momentum lost in a collision

Goes into heat, which is increased momentum of the individual

Molecules within the heated object.

ENERGY

ENERGY IS THE ABILITY TO DO WORK.

WORK IS THE APPLICATION OF A FORCE

OVER A DISTANCE: IT IS ENERGY USED UP

KINETIC ENERGY (energy at work)

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

POTENTIAL ENERGY (available for work)

TOTAL ENERGY=KE + PE = CONSTANT

FORMS OF ENERGY

POTENTIAL

KINETIC

All the rest are versions of the above

HEAT (CAN BE MECHANICAL)

CHEMICAL

LIGHT

ELECTRICAL

NUCLEAR

POWER

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

POWER IS MEASURED IN WATTS

WORK PER UNIT TIME JOULES/SECOND

FORCE 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 ENERGY

REMAINS A CONSTANT.

ENERGY CAN NEITHER BE CREATED

NOR 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

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

Radiation decreases by the square of the distance

Intensity = Io/d2

1- 100

2- 25 = 1/4

3- 11.1= 1/9

4- 6.25= 1/16

5- 4 = 1/25

6- 2.78 = 1/36

100

*

50

*

*

*

*

*

1

3

4

5

6

2

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

- 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 CONSTANT

E1-E2=HEAT INPUT - WORK DONE

(You can’t win)

SECOND LAW: HEAT FLOWS FROM HOT TO COOLER

(You can’t break even)

ENTROPY ALWAYS INCREASES

EVERYTHING 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

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