1. HEAT TRANSFER

2. Heat Transfer Heat always moves from a warmer place to a cooler place.
Hot objects in a cooler room will cool to room temperature.
Cold objects in a warmer room will heat up to room temperature.
Heat Transfer

3. Heat energy travels from hotter places towards cooler places
Heat energy travels from hotter places towards cooler places. There are 3 ways that heat can travel: Conduction Convection Radiation
HEAT TRANSFER

4. HEAT TRANSFER

5. Conduction is the transfer of heat energy from atom to atom by physical contact.
It occurs mostly in solids.
CONDUCTION

6. CONDUCTION

7. Conduction – transfer of thermal energy by collisions with NO overall transfer of matter
Particles vibrate and pass energy to nearby particles, like bumper cars hitting each other
Works best in solids, as the particles are touching.
Thermal conductors – conduct thermal energy well
Ex: Metals
Thermal insulators – do NOT conduct thermal energy well
Ex: Air and other gases
CONDUCTION

8. Conduction in solids is like a bucket brigade
Conduction in solids is like a bucket brigade. Particles (people) stay in one place, but the energy (water) is transferred from one position to the next.
CONDUCTION

9. Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often. In most solids, conduction occurs as particles vibrate in place and push on each other. In metals, conduction is faster because some of the metal’s electrons are free to move about.
Conduction

10. Thermal Conductors A material that conducts thermal energy well.
Example 1: A wire rack on a
grill can burn you because the metal conducts thermal energy so quickly.
Example 2: Pots and pans often are made of copper or aluminum because these are good conductors.
Thermal Conductors

11. A thermal conductor doesn't have to be hot!
Why does a tile floor feel colder than a wooden floor? Both floors are at room temperature. But the tile feels colder because it is a better conductor and transfers thermal energy rapidly away from your skin.
A thermal conductor doesn't have to be hot!

12. Why does metal feel colder than wood, if they are both at the same temperature?
Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

13. Thermal Insulator Example 1: Wood heats up slowly because it is
A thermal insulator conducts thermal energy poorly
Example 1:
Wood heats up slowly because it is
a poor conductor of thermal energy;
therefore a good insulator.
Example 2:
Air found in between panes of a
double-paned window insulates
the house in winter/keeps heat out in
summer
Thermal Insulator

14. Examples 3 & 4:
Wool
Styrofoam cups
Both use trapped air to SLOW DOWN conduction

15. Convection is the transfer of heat energy by the movement of the atoms themselves. It occurs in fluids (gases and liquids).
CONVECTION

16. Convection The transfer of thermal energy when particles of a fluid move from one place to another.
When fluids heat up they expand, and thus become less dense.
Fluids less dense than surroundings rise.
Fluids more dense than surroundings sink.
Convection

17. The particles spread out and become less dense.
Convection
What happens to the particles in a liquid or a gas when you heat them? Liquids and gases are called fluids
The particles spread out and become less dense. .
This causes expansion and fluid movement.

18. Water movement Convection current Cooler water sinks Hot water rises
Cools at the surface
Convection current
Cooler water sinks
Hot water rises

19. Convection is like people (particles) carrying water (energy) to the fire. There is movement of the particles AND of the heat.
Convection

20. CONVECTION CURRENTS

21. CONVECTION CURRENT

22. Convection – transfer of thermal energy when particles of a fluid MOVE from one place to another.
Particles transfer thermal energy from hot to cold.
When fluids heat up they expand, and thus become less dense.
Fluids less dense than surroundings rise.
Fluids more dense than surroundings sink.
CONVECTION

23. The third method of heat transfer
There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection.
How does heat energy get from the Sun to the Earth?
RADIATION ?

24. RADIATION Radiation is the transfer of heat energy by waves.
NO atoms, molecules or matter are needed for radiation heat transfer.
Heat can be
transferred
through the
vacuum of outer
space.
RADIATION

25. Radiation moves across space without being carried on particles (no buckets). It’s like a fire hose squirting water (energy).
RADIATION

26. Radiation – transfer of energy by electromagnetic waves moving through space
No matter required – can pass through a VACUUM (Space!)
All objects radiate energy, as all objects have some heat (nothing is at 0 °K!)
Radiation is often called radiant heat.
What do you think happens to the rate of radiation as an object’s temperature increases?
RADIATION

27. Radiation experiment
Four containers were filled with warm water. Which container would have the warmest water after ten minutes?
Shiny metal
Dull metal
Dull black
Shiny black
The shiny metal container would be the warmest after ten minutes because its shiny surface reflects heat back into the container so less is lost. The dull black container would be the coolest because it is the best at radiating heat.

28. Absorption experiment
Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes?
Shiny metal
Dull metal
Dull black
Shiny black
The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation.
dull black
radiation
shiny metal
absorbing

29. RADIANT ENERGY What can objects “do” with radiant energy?
Absorb it – when radiation is absorbed
thermal energy increases (dark surfaces)
2. Reflect it – bounce it back (shiny things)
3. Transmit it – let it though (windows in a
greenhouse)
RADIANT ENERGY

30. RADIATION HEATS THE EARTH

31. RADIATION

32. Body heat is thermal energy radiated in the infrared portion of the spectrum
RADIATION

33. Popcorn- How can we cook it?
1) Radiation→ put popcorn bag in microwave
2) Convection → put popcorn in air popper
3) Conduction → put popcorn and
oil in a pan on
the stove