Thermal Energy
Transfer and absorption
Thermodynamics
Thermodynamics-study of heat
transformations into other forms of
energy
Heat
Fire dissipates heat
Does not absorb heat
Heat always flows from a hotter to cooler
Heat flowing from hotter to cooler
Grease fire
http://www.gocolumbiamo.com/Fire/Educat
ional/stovefires.php
http://www.teachertube.com/view_video.ph
p?viewkey=d76c5ec1acefe6d433b6
http://www.teachertube.com/view_video.ph
p?viewkey=e0da400d9b98c254b9fc
Thermal Energy
Thermal Energy- total energy of the molecules
Temperature- related to average energy per
molecule
Thermal Energy and Temperature
Temperature-quantifies the average kinetic
energy of the particles in an object
The warmer an object the more kinetic energy it
has.
KEavg=KEt/(number of particles)
Thermal Energy- proportional to the number
of particles
Equilibrium and Thermometry
Hot = particles move faster = more thermal energy
Conduction-transfer of kinetic energy when particles collide
energy transferred from a warmer object to a colder object
How much energy is in an object at 0 Kelvin (absolute zero)?
“Scientists put a light wave on hold”
http://www.msnbc.msn.com/id/3077366/
Equilibrium and Thermometry
Thermal Equilibrium- the state in which the
rate of energy flow between two objects is
equal and the objects are at the same
temperature
Same temperature
Temperature Scales
CelsiusThe zero point is the freezing point of water
The 100 point is the boiling point of water
Kelvin
The zero point is where all thermal energy has been
removed. No lower possible temperature, No
motion in the atoms. Absolute Zero
0 K =- 273.15 C
Tc + 273 = TK
Temperature Scales
Fahrenheit
The zero point is determined by a frigorific mixture
of ice, water, and ammonium chloride (a salt). The
mixture automatically stabilizes its temperature at
0 °F
The second point is the 32 degree found by putting
the thermometer in still water as ice is just forming
on the surface.
The third point, the 96 degree, was the level of the
liquid in the thermometer when held in the mouth
or under the armpit. (Has been since adjusted to
98.6)
Three Temperature Scales
Three Temperature Scales
Heat
And how it transferred
Heat
Heat-energy that always flows from the
hotter object to the cooler object.
“Left to itself heat never flows from a colder object
to a hotter object.”
Variable ‘Q’ denotes heat
Q is in joules or J
Flow of Thermal Energy
Conduction
Convection
Radiation
Conduction
Heat is transferred (conducted) through
particles that are in direct contact with
each other.
Convection
The motion of fluid in a liquid or gas caused by
temperature differences
Hotter fluids/gases rise.
Cooler fluids/gases sink.
“Real power from nothing but hot air”
http://www.guardian.co.uk/environment/2002/aug/19/energy.renewableenergy
Radiation
The transfer of energy by electromagnetic
waves
Does not require contact
Travels at 3x10^8 m/s
Nuclear Test Site, Ground Zero
Specific Heat
The amount of energy that must be added to
a material to raise the temperature of a
unit mass by one temperature unit.
Heat Transfer
Q = mC∆T = mC(Tf –Ti)
Q = heat
m = mass
C = specific heat
T = temperature
Temperature intervals for Kelvin and Celsius
are the same, (i.e. ∆T is the same)
Ex 1, pg318
3-5 , pg 319
Conservation of Energy
The total energy in an isolated, closed system never changes.
EA + EB = constant
1)E  q  mC T
2) mAC A TA  mB CB TB  0
mAC ATA  mB CBTB
3)T f 
mAC A  mB CB
Ex 2, pg321
6-7, pg321
Homework
Pg 322
# 10, 12, 16, 17
Pg 336
#37, 39, 50, 52, 53, 57
Changes of State and the Laws of
Thermodynamics
Change in state changes structure and the
way in which atoms store thermal energy
States of matter
Solid
Liquid
Gas
Plasma
Change-of-State
Changes of State
Melting Point
Heat of Fusion
Q=mHf
Boiling Point
Heat of Vaporization
Q=mHv
Condensation Point
Freezing Point
Heat = Q in Joules J
Thermal energy
Increase thermal energy
Increases particle speed
Causes more freedom of movement
Change-of-State
All thermal energy added goes to
overcome the forces holding the
particles together.
The temperature does not increase
Melting
Boiling
The First Law of Thermal Dynamics
Change in thermal energy is equal to the heat
added minus the work done
∆U=Q-W
Where
∆U is the change in thermal energy
Q is the heat added
W is the work done
Efficiency
W/QH
How your refrigerator works
The Second Law of Thermal Dynamics
Natural processes go in a direction that
maintains of increases the total entropy of
the universe.
Things get more disordered over time,
assuming time is going forward.
The Animate and the Inanimate
(available on class website)
Read Pg 4-8,42
Explain what it means
One page write-up
Entropy
Entropy – the measure of disorder in a system
Change in Entropy – is equal to the heat
added divided by the temperature in
kelvins
∆S=Q/T
The measure of unavailability of useful
energy
Temperature and Thermal Energy
Describe thermal energy and compare it to
potential and kinetic energies.
Distinguish between temperature and
thermal energy
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Elements
www.animationfactory.com