1. Chapter 22: Heat Transfer
All about thermal energy moving – heat flow – how does it work?

2. Too Hot to Handle Thermal Energy Transferred in 3 ways Conduction
Convection
Radiation
Ask them if they know the 3 ways first…

3. Conducting Business Conduction
Heat transferred through CONTACT – atoms of one material crash into atoms of other material
Conductors are good at it
Insulators are bad at it
What is heat? What is temperature? Conduction is atoms crashing – momentum being transferred
Do desk example – touch metal, touch top
Show Hewitt videos – air is insulator and walking on hot coals
Styrofoam, down jackets, house insulation, double pane windows, metal vs. plastic windows, vacuum bottles

4. Convection Convection Transfer of energy through fluids
Not so much energy transfer as matter transfer
Archimedes’ principle applied
Convection currents produce winds
Show Eureka Video – Show example on the board – lake wind examples – boiling water example – Sun example
Works in all fluids!

5. Full of Cold Air Air is cooler at higher altitudes
Less pressure so: gases are able to expand
Lower density = less kinetic energy = lower temperature
Air is very low altitudes
This is why it is cold at higher altitudes – cold in Denver, on Everest, warm in Death valley & Jordan Valley
Death Valley

6. You’re So Radiant Forms of radiant energy
Microwaves UV IR
Radio
Visible
Gamma
Heat transfer from sun is radiation
Energy transmitted via radiation is radiant energy
Doesn’t have to be touching, doesn’t need air or fluid – only way energy can enter from outside the planet

7. Riding the Waves Good absorbers = Good Emitters
Low temperature emit long wavelengths
High temperature emit short wavelengths
We absorb IR waves (heat lamp)
Remember Movie at start of semester – this is black body radiation!!! Only depends on temperature
Heat lamp – absorb & emit IR waves

8. Radiant Energy Absorbing and Reflecting are opposites
Light colors reflect:
radiant energy
All wavelengths
Dark colors absorb:
Silver coffee & drink pitchers, black clothing, white clothing
Coffee/Cream NTQ

9. Newton’s Cool R~∆T Newton’s law of cooling
Rate of cooling for an object is proportional to the difference in temperature
True for heating also
Very hot things cool faster than just warm things – More energy is transferred per bigger difference

10. Keeping Warm Greenhouse effect
Radiant energy entering is greater than Radiant energy leaving
Works like this…

11. How a Green House Works Greenhouse effect
Short waves from sun pass through glass & are absorbed inside the green house
Long waves emitted by greenhouse & plants are absorbed & remitted inward by the glass
You may never have been in a green house – but same thing happens with cars and houses. – keeps green house hot, eventually enough heat rise to allow escape by conduction, radiation

12. The Earth as a Greenhouse
Sun is very hot; sends short waves of energy to Earth
Sun waves pass through atmosphere
Earth is cooler; sends out longer waves
Water vapor and CO2 prevent terrestrial radiation from leaving