Thermal Energy
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Transcript of Thermal Energy
Thermal Energy
• Temperature– THE AVERAGE KINETIC ENERGY OF AN OBJECT.
• Average motion energy
• Thermal Energy– THE TOTAL KINETIC + POTENTIAL ENERGY IN AN
OBJECT.• Energy of stored bonds + motion
• Temperature Reference Points
• Freezing Point of Water– 0 °C or 32°F
• Boiling Point of Water– 100°C or 212°F
0 100 Temperature (°C)
212
32
Tem
pera
ture
(°F)
Temperature ConversionsTK = Temperature in KelvinTC = Temperature in °CTF = Temperature in °F
Temperature Conversions
HEAT TRANSFER
1. Which object has the greatest temperature?
2. Which object has the greatest average kinetic energy?
3. Which object has the greatest total kinetic energy?
4. Which object has the greatest Thermal Energy?
5. Which object, left on its own, in outer space, has the greatest heat?
6. Which object, connected to the table, has the greatest heat transfer?
A. 97°C50 mL
B. 7°C1 L
C.-2°C
1000 kL
D.None of these
Heat• HEAT = THERMAL ENERGY THAT IS
TRANSFERRED FROM ONE OBJECT TO ANOTHER.
• HEAT ALWAYS FLOWS FROM THE HIGHER TEMPERATURE TO THE LOWER TEMPERATURE
• Touch the leg of your chair and the leg of your desk. Which one is colder?
Pizza Capacity
• Think and Explain? When I throw my pizza into the microwave to
warm it up, it isn’t the same temperature throughout. Why?
Heat Capacity
• All substances will change temperature as they gain thermal energy.
• HEAT CAPACITY = THE AMOUNT OF TEMPERATURE CHANGE TO A HEATED OBJECT DEPENDS ON THE OBJECT AND THE MASS.
Modes of Heat Transfer
• The three methods of Heat Transfer
– CONDUCTION
– CONVECTION
– RADIATION
Conduction
• CONDUCTION = THERMAL ENERGY TRANSFERRED BY THE COLLOSIONS OF PARTICLES
• CONDUCTION REQUIRES CONTACT
– It is an exchange of energy between atoms and electrons by collisions
– Less energetic particles gain energy during collisions with more energetic particles.
MaterialsListed are common materials. Better conductors have a higher thermal conductivity
Demo -
POOR CONDUCTOR = GOOD INSULATOR
Conduction Examples• Why is the tile cold
and the carpet feel warm?
• Because the tile is a better conductor and it has a greater heat capacity
Convection• What is convection?
• THERMAL ENERGY TRANSFERRED BY A CURRENT OF FLUID
• REQUIRES A FLUID(Gas/Liquid)
– When the movement results from differences in density, it is called natural convection
– When the movement is forced by a fan or a pump, it is called forced convection
Convection Heating• An example of
natural convection
• Explain what is happening
• Water Temp Demo
Convection Current Example• What is the forced
convection?
• What is the natural convection?
Weather – due to natural convection
Radiation
• RADIATION = THERMAL ENERGY TRANSFERRED BY ELECTROMAGNETIC WAVES
• RADIATION DOES NOT REQUIRE CONTACT
• All objects radiate (give off) energy continuously in the form of electromagnetic waves due to thermal vibrations of the molecules
Thermal Expansion
• When an object is heated, it’s particles speed up and spread apart, making the object expand.
• Demo -
• Uses: Cavities, Bridges, Sidewalks Lines• Downsides - potholes
Radiation example
• No physical contact is necessary• The electromagnetic waves carry the energy• The heat transfer cannot be accounted for by
conduction or convection (thru space)
States of Matter
Picture Volume Shape Kinetic Energy
Inter-molecular
Force
Gas
Liquid
Solid
Phase SummaryPicture Definite
VolumeDefinite Shape
Kinetic Energy
Inter-molecular
Force
Gas No NoHigh
Sometimes bounce off
one another
None
Liquid Yes NoMedium
Roll, Bounce off one another
Weak
Solid Yes YesLow
Shake back and Forth
Strong
States of Matter Notes
• These are found online at • http://prezi.com/_2quyv8zpnzq/notes-states-
of-matter/
• (Look at these or you’ll be sorry).
Deposition = Frost
Condensation
Amorphous
Definite Shape
No Definite Shape
Fluid
Molecules in motion
Vaporziation
Melti
ng
CrystallineFre
ezing
Definite Volume
No Definite Volume
Least Kinetic energy
Medium Kinetic energy
Property of Viscosity Highest Kinetic Energy
Sublimation = Dry Ice
Phase Change Graphs
0 1 2 3 4 5 Thermal Energy
150
100
50
0
Tem
pera
ture
(°C)
Thermal Energy and Phase Changes
Freezing
Liqui
d
Gas
Condensation
Melting
Solid
Vaporization
Phase Change Process (S & L)• Melting – THERMAL ENERGY IS USED TO BREAK BONDS
– The bonds that hold molecules in vibrating lattice structure are breaking.
–The Intermolecular Forces Lessen
• Freezing – THERMAL ENERGY IS USED TO CREATE BONDS AND HOLD MOLECULES IN PLACE– The bonds that will hold molecules in position are forming–The Intermolecular Forces Increase
–Melting Point – THE TEMPERATURE AT WHICH AN OBJECT EITHER MELTS OR FREEZES.
Evaporation = Escape• Brant’s Maximum Security Penitentiary for
Incarcerated Dress Code Violators and Others.• If the highest IQ’s escape, what happens to
the average Penitentiary IQ.– Up– Down– Same
VAPORIZATION (L – G)
• EVAPORATION – A CHANGE IN PHASE FROM LIQUID TO GAS AT THE SURFACE.– This cools the remaining liquid!
• BOILING – A CHANGE IN PHASE FROME LIQUID TO GAS BELOW THE SURFACE.– This cools the remaining liquid!
• Boiling Point – THE TEMPERATURE THAT AN OBJECT VAPORIZES OR CONDENSES.
Condensation (G L)• CONDENSATION – A CHANGE OF PHASE FROM GAS TO
LIQUID.
• This is a WARMING PROCESS for the liquid.
• Gas molecules strike surface of liquid and give up so much energy that they can’t stay in gaseous phase
• ExamplesDroplets forming on mirrorDroplets on glass of water
Condensation = Captured• The smart kids sneak out of a convocation in
the gym and join the prison of ISS. What happens to the average IQ of the prison?– Up– Down– Same
Phase Changes with the Gizmo
• The differences with this type of graph, and the basic phase change graph is that the time is the x-axis instead of changing thermal energy.
• Hint: In these graphs Mr. Nuetzel had an initial setup, then didn’t change any of the settings after starting it.
Phase Change GizmoWith this setup, what will happen to the temp. graph?
Phase Change GizmoWith this setup, what will happen to the temp. graph?
Phase Change GizmoWith this setup, what will happen to the temp. graph?
Phase Change GizmoWith this setup, what will happen to the temp. graph?
What’s the difference between these two graphs?
What’s the difference between these two graphs?
Phase Change GizmoWith this setup, what will happen to the temp. graph?
Interpreting Graphs
• Hint – Mr. Nuetzel didn’t keep the RATE of heat transfer constant in these graphs.
What is happening in this graph?
What is happening in this graph?
What is the difference in these graphs?
What is happening in this graph?
What is happening in this graph?
What is happening in this graph?
Acting Out Phase Changes
• Get in a group of 8-12 students. You will have 2 minutes to decide how you want to act out one of the phase changes that H2O can go through with either an addition or subtraction of thermal energy.
• Demonstrate your skit to the class.
Review Discussion Questions
• Explain in detail and use the thermal energy vocabulary.
• When I throw my pizza into the microwave to warm it up, it isn’t the same temperature throughout. Why?
• How is the house heated?
• How does a thermometer work?