1. Heat and heat transfer

2. Temperature (T) Absolute zero Freezing of water Boiling of water
-Measures how hot something is
Measurement of average (translational) kinetic energy
NOT total kinetic energy (2 different size volumes of water)
degrees Celsius or degrees Centigrade or °C
Fahrenheit scale
Kelvin Scale
Absolute zero
Freezing of water
Boiling of water
-273 °C
0 °C
100 °C
-460 °F
32 °F
212 °F
0 °K
273 °K
373 °K

3. Heat (Q) Objects DO NOT have heat Heat is a transfer of thermal energy
Heat is NOT temperature! They are not interchangeable!
Heat is like work…
Work is the transfer/changing of mechanical energy
Heat flows from hot objects to cold objects
Just like how water flows, it goes from high to low

4. Thermal Equilibrium
When two objects are in thermal contact, they will exchange heat from the hot object to the cold object until they reach thermal equilibrium.
- Until they are the same temperature
A thermometer reaches thermal equilibrium with the material it is in.

5. Thermal Expansion Materials expand when heated and shrink when cooled
- there are a few exceptions: Water

6. Transfer of heat
When heat is transferred, it is pulled from hotter objects into colder objects. NEVER THE OTHER WAY AROUND! Alton Brown’s Explanation of the transfer of heat and thermoses
Conduction
Convection
Radiation

7. Insulators Vs. Conductors
Which of the following are good conductors:
Aluminium
Glass
Copper
Iron
Polythene
Cardboard
Nickel
Paper
Chocolate
Steel.

8. Good
Aluminium
Copper
Iron
Nickel
Steel
Bad
Glass
Polythene
Cardboard
Paper
Chocolate

9. Insulator is the special posh sciencey name for a poor conductor.
For the following objects, state whether you would want them to be made out of a good conductor, or a good insulator:
The bottom of a saucepan
The handle of a saucepan
A duvet/quilt
An ice cream tub

10. Good conductors
Bottom of a saucepan
Good Insulators
Saucepan handle
Duvet/quilt
Ice cream tub

11. Conduction

12. Conduction Heat transfers along an object metals have high conduction
Stir your hot soup with a metal spoon
Pretty soon you need a pot holder because the end of the spoon you are holding gets hot
This is heat transfer by conduction
Energy travels up the spoon from the end in the hot soup to the end in your hand
Heat transfers along an object
metals have high conduction
Heating through touch/ contact

13. Conduction
Metals have some electrons that are very loosely bound to the atoms in the material These electrons can move easily and can rapidly pick up additional kinetic energy Metals are good conductors Wood and plastic don’t have loosely bound electrons, so they are poor conductors

14. So…
When you eat a popsicle, why does the stick feel warmer than the popsicle part if they were both in the freezer together?

15. Convection Hot air rises because… It is less dense than cold air Why?
When something is heated the particles move around more and spread out.
Why does cold gas and liquid fall?
When it cools the particles move around less, move closer together, and therefore become more dense.

16. Convection Convection A phenomenon in fluids
Instead of having energy moved by successive collisions of electrons, atoms and molecules, the fluid itself is set into motion called a current
These moving fluid currents are convection

17. Convection
When the radiator heats the air, it becomes less dense and rises
Cool air moves in to replace the air that rose
This generates the air flow
So radiators don’t need a fan to stir the air and to distribute heat throughout a room
The rising air cools until its density matches that of the surrounding air

18. Convection
We take advantage of the cooling that occurs during an expansion
We make refrigerators and air conditioners operate by forcing gas under pressure through a small hole and expanding it into an empty space

19. Convection
Explains why breezes come from the ocean in the day and from the land at night

20. Radiation

21. Radiation Radiation Energy carried by electromagnetic waves
Light, microwaves, radio waves, x-rays
Wavelength is related to vibration frequency

22. Radiation
Every object is emitting electromagnetic waves regardless of temperature
Things we can see from their own radiation are very hot to have energy emitted in the visible region of the spectrum
Most things emit primarily in the infrared
Night vision goggles, etc.

23. Radiation Interior of a car on a sunny day
Sunlight comes in as visible light
Seats and interior are much cooler so they radiate in the infrared instead of visible
Glass in the windows blocks infrared so energy can’t get out
Car interior heats up!

24. Radiation A good absorber reflects very little energy
Think about dark pavement
A poor absorber reflects a lot of energy
Think about snow that doesn’t melt in sunshine even though 1400 watts/meter2 are hitting it

25. The diagram below represents a saucepan on a hot plate.
The saucepan is partially filled with water and the hot plate is turned on. After some time, the air at point X above the pan becomes hot.
a. Explain how heat is transferred from the hot plate to the base of the saucepan.
b. Explain how heat is transferred from the base of the saucepan to all of the water in the saucepan.
c. Explain how heat is transferred from the hot water to the air at point X.

26. The diagram below represents a home heating system.
a. Give an example of where heat convection occurs in this system.
b. Give an example of where heat radiation occurs in this system.
c. What purpose do the ceiling fans serve in helping to heat the home?
d. Explain why pipes carrying hot water run along the floors of the rooms instead of the ceilings.

27. Change of Phase
When heat is added to, or taken away from a substance, the temperature of the substance will either increase or decrease.
However, when a substance changes phase (like when water boils or freezes), heat is need to change the properties of the substance.
When this happens, the temperature of the substance will not change, but the substance will change phase.

28. Change of Phase
This is known as the latent heat
80 cal/g
540 cal/g

29. Change of Phase Evaporation from liquid to gas at a surface
requires energy (heat) to vaporize a liquid
Absorbs heat
Condensation
from gas to liquid
gives off heat
fog and clouds are condensed water vapor
Boiling is a special case of evaporation
takes place below the surface
100 °C for water at atmospheric pressure
temperature of solid
and liquid are the same
540 cal/g to evaporated water
Called Heat of vaporization

30. Change of Phase Freezing from liquid to solid
losses energy (heat) to freeze a liquid
Melting
From solid to liquid
Requires heat to melt a solid
Absorbs heat
temperature remains constant
80 cal/g of heat lost to freeze water
Called Heat of fusion

31. Change of Phase Sublimation Deposition from solid to gas
snow can turn to gas directly in winter
Think of dry ice
Deposition
from gas to solid
Water vapor can turn into snow flakes
through deposition

32. Latent Heat
Latent Heat: The amount of heat required to change the phase of a material.
Dictated by either the Heat of vaporization or the Heat of Fusion
Heat of vaporizations- the heat required to change between liquid and gas (in either direction)
Heat of fusion- the heat required to change between solid and liquid (in either direction)
The temperature of an object doesn’t change when it is changing phase, that heat energy actually goes to changing the phase.