Transcript Heat & Energy

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
WORK
WORK IS FORCE OVER A DISTANCE
NEWTON-METRE
JOULE
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
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
Radiation decreases by the square of the distance
Intensity =
Io/d2
100
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50
123456-
100
25 = 1/4
11.1= 1/9
6.25= 1/16
4 = 1/25
2.78 = 1/36
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2
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4
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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 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