Transcript Burlwood - Douglas County
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.
KE avg =KE t /(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
Celsius The 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 T c + 273 = T K
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 = m C∆T = m C(T f –T i ) 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.
E A + E B = constant
Ex 2, pg321 6-7, pg321 1)
q
2)
m C
A A
3)
T
f
A
m C T
A A A
m C
A A
m C
B B
B
m C T
B
m C
B B B B
0
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= Q= m m H f Boiling Point Heat of Vaporization Hv 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 Boiling Melting
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/Q H
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
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