1. Heat Transfer Objectives: Heat Transfer Phase Change Relative Humidity
Thermal Expansion

2. Heat Transfer Mixing (requires air or other mixing particles)
Convection
Examples: warming soup on stove top
Conduction
Direct Contact
Examples: tip of a needle over flame
Radiation
No substance required
Examples: warming soup in the microwave oven, heat coming from the sun

3. Newton’s Law of Cooling
The larger the temperature difference, the faster the cooling/warming up.
Question: In a cold winter day, you put out a bucket full of water. Which one would freeze faster: a bucket full of
(a) Hot water (b) cold water (c) the same

4. Changes of State Q1. What is the melting point for ice?
Q2. What is the condensation point for water vapor?
Vapor

5. Evaporation and Condensation
Saturation
When evaporation and condensation reach equilibrium
The warmer the air, the more water molecules can contain
Question: You come out of the shower you notice the bathroom mirror becomes quickly fogged up. What happened?
The fraction of water molecules in air relative to the maximum possible water molecules in air at a given T
Relative Humidy

6. Thermal Expansion As temperature rises, dimensions expand
Railroad tracks, Bridge metal rods
Linear
Volume
Gasoline inside tank
Q9. As you heat a rectangular plate, what happens to its dimensions?
Q10. If the plate has a hole, what happens to the dimensions of the hole?

7. Thermal Expansion As temperature rises, dimensions expand
When stringing telephone lines between poles in the summer, it is advisable to allow the lines to
sag.
be taut.
be close to the ground.
allow ample space for birds.

8. Anomalous Behavior of Water
Expands or contracts?
Ice melting
contracts
Icy water warming up ( 0 – 4 C)
contracts
Water warming up (4 C and above)
expands
Question. At what temperature is water most dense?
Question. What is the temperature of seawater at the bottom of the ocean?

9. Puzzles P6. Frozen food will warm up faster in a hot or cooler room?
P7. You fill you glass of water to the brim with water at 1C. You let it warm up to 4C. What will happen to the water?
It will spill over the cup
There will be room to add more water
Nothing will change
P3. Can you heat up a bowl of soup on a hot stove in the International Space Station?
P4. On a hot summer day, you walk into a cooled room and your glasses become fogged up. Why?
P5. In the winter, you can “see” your breath. Why can you not see in in the summer?