1. Energy Transfer as Heat

2. S8P2 d. Describe how heat can be transferred through matter by collisions of atoms (conduction) or through space (radiation). In a liquid or gas, currents will facilitate the transfer of heat (convection).

3. Background
All forms of matter, whether solid, liquid, or gas, are composed of atoms or molecules in constant motion
Because of this constant motion, all atoms have thermal (heat) energy
Whenever a substance is heated, the atoms move faster and faster
When a substance is cooled, the atoms move slower and slower
The “average motion” of the atoms that we sense is what we call temperature
Temperature and heat ARE NOT technically the same thing
Temperature is the average motion of atoms and molecules; heat is the energy that flows due to temperature differences

4. Lesson Essential Question:
How is energy transferred as heat?

5. The transfer of energy between the particles of two objects due to a temperature difference between the two objects is called heat.

6. The transfer of energy always takes place from a substance at a higher temperature to a substance at a lower temperature
Temperature is an indicator of the particles’ average kinetic energy; therefore, you can use it to predict which way energy will be transferred
The greater the difference in the temperatures of two objects, the more energy that will transfer as heat

7. Energy can be transferred as heat in three ways:
Conduction
Convection
Radiation

8. Conduction

9. Conduction
Conduction is the transfer of energy that occurs when molecules bump into one another (heat transfer from one atom to another within a substance).

10. Solid at Different Temperatures
Conduction
Molecules are always in motion, but molecules in warmer objects move faster than molecules in cooler objects.
Solid at Different Temperatures

11. Conduction
When objects are in contact, energy is transferred from warmer objects to cooler objects.

12. Conduction
Example of conduction: A spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon
Conduction is most effective in solids, but it can happen in fluids. Gases and liquids are generally poor conductors of heat because their molecules are farther apart than are the molecules in solids. Therefore, neighboring molecules in a gas or in a liquid are less affected by the increased motions of heated molecules, and consequently heat is not conducted rapidly.

13. Conduction
When you heat a metal strip at one end, the heat travels to the other end.
As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this?
Conduction

14. Conduction
Why does the lady in the pink dress drop her roasting stick when the lady in the blue dress does not?

15. When heat is conducted, it is led from the heat source by traveling along a physical object. The young woman in the pink dress was using a straightened out coat hanger wire to cook her marshmallow. Metal is a good conductor of heat. The heat from the fire traveled along the thick metal wire. The wire got so hot that the girl had to let go of it. The young girl in the blue dress is using a wooden rod to hold her marshmallow. Wood does not conduct heat well. The wood in her hand is still cool and the marshmallows are almost done!

16. Conduction
Any material through which energy can be easily transferred as heat is called a conductor
What determines how well a substance conducts is whether it is a gas, liquid, or solid
Gases are extremely poor conductors because their particles are far apart
Liquids conduct better than gases, but they are still not very effective conductors
Some solids, like rubber and wood, conduct energy about as well as liquids
Metals such as copper and silver conduct heat transfer very well
Some solids conduct better than others
In general, metals are better conductors than nonmetals

17. Conduction
A material that is a poor conductor that is used to reduce or stop energy is called an insulator
Ex. Wood

18. Conductivity Chart

19. Convection

20. Convection
Convection is the transfer of heat by the flow of material. Convection circulates heat.

21. Convection Heat moves with the fluid
Warmer portions are less dense and therefore rise; cooler portions fall because they are denser. When the atoms at the top cool down, they become more dense and fall and vice versa for the warmer atoms. Hence a continuous cycle
The cycle of a heated fluid that rises and then cools and falls is called a convection current

22. Fluid movement
Cooler, more d____, fluids sink through w_____, less dense fluids.
ense
armer
In effect warmer liquids and gases r___ up.
ise
Cooler liquids and gases s___.
ink

23. Convection occurs mostly in gas or liquid.

24. Convection

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

26. Radiation

27. Radiation
Radiation is energy that is transferred in the form of rays or electromagnetic waves. This includes infrared radiation, visible light, and ultraviolet rays.

28. Radiation What happens in space?
There are no solids touching the sun for conduction to occur
There are no fluids in space for convection to occur
Therefore, heat travels by radiation

29. Conduction, Convection, and Radiation together distribute the Sun’s heat throughout the Earth