1. Heat Transfer
I Like it Hot!!

2. (Room temperature is about 25 Degrees C)
Question
Q: If a cup of hot chocolate and an ice cube were left on the table in this room what would happen their temperature? Why?
A: The cup of hot chocolate will cool until it reaches “room temperature.”
A: The ice cube will melt and then the liquid will warm to “room temperature.”
(Room temperature is about 25 Degrees C)

3. Heat Transfer The cooler air warms up and the mug cools down
Heat always moves from a warmer place to a cooler place.
So:
Hot objects in a cooler room will cool to room temperature.
Heat Energy
Heated liquid/air
The cooler air warms up and the mug cools down
Cooler air
The air outside the mug is cooler
than the air inside the mug. So the heated air
moves out of the mug into the cooler air

4. All solids (ice) melt when they gain enough heat energy
Heat Transfer
Heat always moves from a warmer place to a cooler place. So:
Cold objects in a warmer room will heat up to room temperature.
Heat Energy
All solids (ice) melt when they
gain enough heat energy

5. Conduction: (Touch) Movement through direct contact
Heat Transfer Methods
Heat moves from one place to another by
Conduction: (Touch) Movement through direct contact
Convection: (Fluid) Circular motion of heated fluid material
Radiation: (Light) Light waves through a medium or vacuum

6. Heat Transfer through Touch
Conduction
Heat Transfer through Touch

7. Ever touched a hot pan handle? How did it feel?
How did the heat from the flame transfer to your hand?

8. Conduction
When you heat a metal strip at one end, the heat travels to the other end.
So it’s no wonder that you can hold metal
over a flame without it burning your hand for
a few seconds, but after that…OUCH!!!
Metal Bar
Watch as the atoms closest to the
flame gain more energy first and
the energy simply spreads out
Heat Energy
It takes a little time, but the Heat
Energy spreads out and the
metal gets “hotter”
As you heat the metal, the atoms vibrate faster, these vibrations make the adjacent atoms vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat.
Demo: “Human Conduction!”
Demo: “Butter Melting”

9. Why Metals heat up so fast?
In addition to atom vibrations, the electrons for metal atoms can “drift”; are free to move around within the metal.
= electron
When the metal is heated, the electrons gain kinetic energy and transfer it throughout the metal.
Heat
Energy
“Insulators”, such as wood and plastic, do not have drifting electrons which is why they do not conduct heat as well as metals.

10. Heat Transfer through Fluids
Convection
Heat Transfer through Fluids

11. Density Re-Cap
Did the number of atoms change in the Balloon? Why?

12. Convection
Cooler, more dense, fluids sink through warmer, less dense fluids.
In effect warmer liquids and gases rise up.
Cooler liquids and gases sink.
Demo: Red, White & Blue Water

13. Convection: Water movement
That’s why its Called a “Convection Current!”
Convection: Water movement
Hot water rises
Warms back up again.
Hot water rises back up
Cools at the surface
Cooler water sinks
Heat source
Demo: Oil & Thyme

15. Where is the freezer compartment put in a fridge?
Cold air sinks
Where is the freezer compartment put in a fridge?
Freezer compartment
It is warmer at the bottom, so this warmer air rises and a convection current is set up.
It is put at the top, because cool air sinks, so it cools the food on the way down.

16. Why is it windy at the seaside?
And we get convection currents of air!
So it moves sideways towards the shore and we feel this motion as a breeze
When the cool air reaches the surface of the water, there is nowhere else for it to go
As the cool breeze reaches the land, it heats up, and rises as well!

17. The third method of heat transfer
How does heat energy get from the Sun to the Earth?
There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. ?
RADIATION=The transfer of heat through electro-magnetic waves!
Also Known as “Light!”

18. Electromagnetic +/- +/-
Energy from the motion of a moving charged particle in the atoms disturbs the electromagnetic fields which effects other charged particles in other atoms.
Electromagnetic Fields
Radiation
+/-
+/-
Work = Force x Distance

19. Radiation help keep our planet warm

20. There is a lot of energy in Solar Radiation

21. Human Uses for Radiation:
You can also use radiation to get warm on a camping trip!

22. Human Uses for Radiation:
You can also use radiation to warm up our food!

23. Radiation questions Q: Why are houses painted white in hot countries?
A: White reflects heat radiation and keeps the house cooler.
Q: Why are shiny foil blankets wrapped around marathon runners at the end of a race?
A: The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.