Thermal Energy & Heat

Temperature

Temperature measure of the

average KE (motion) of the particles

Going from Celsius to Fahrenheit

oF = 9/5 (oC) + 32

Convert 37 oC to oF.oF = 9/5oC + 32oF = 9/5(37oC) + 32

= 66.6 + 32

= 98.6oF

Going from Fahrenheit to Celsius

oC = 5/9 (oF – 32)

Convert 68oF to oCoC = 5/9(oF – 32)oC = 5/9(68 – 32)

= 5/9(36)

= 20 oC

Thermal Energy

Thermal Energy the total energy of the particles in

a material (KE + PE) KE - movement of particles PE - forces within or between particles due to position

depends on temperature, mass, and type of substance

Thermal Energy

Which beaker of water has more thermal energy? B - same temperature, more mass

200 mL

80ºC

A400 mL

80ºC

B

Heat Transfer

Heat thermal energy that flows from

a warmer material to a cooler material

Heat is... measured in joules (J) a transfer of energy

Heat TransferWhy does A feel hot and B feel cold?

80ºC

A

10ºC

B

Heat flows from A to your hand = hot. Heat flows from your hand to B = cold.

Heat Transfer Heat is always

transferred from hot to cold.

Insulators slow the transfer of heat due to air pockets.

Conductors easily allow the transfer of heat, like metals.

Heat is transferred by radiation, conduction, and convection.

Radiation Transfer of heat

through electromagnetic radiation (light from stars or light bulbs).

Transferred in all directions.

No contact required! Dark or dull objects

absorb more than light or shiny objects do.

How does heat get from one place to another?

1. Radiation

2. Conduction

3. Convection

Conduction

Heat is transferred due to objects touching each other or through collisions.

Occurs best in solids. Heat continues to be

transferred until both objects reach the same temperature, called a thermal equilibrium.

Heat Transfer

Insulators slow the transfer of heat due to air pockets.

Conductors easily allow the transfer of heat, like metals.

Aluminum at 25 C Compressed foam at 25 C

Skin at 37 C Skin at 37 C

Feels “cold” Feels “warm”

Aluminum at 25 C Compressed foam at 25 C

Ice at 0 C Ice at 0 C

Question???

Nick bought a bowl of soup in Styrofoam cup. He noticed that the metal spoon handle sticking out of the soup became too hot to touch, but he could hold the cup in his hand comfortably. Explain why the Styrofoam cup and spoon did not feel the same.

How did you do?

You should CORRECTLY use the following concepts: Molecules, Heat/Energy Transfer, Conductor, Insulator

The warmer molecules in the soup transfer heat energy to the spoon. The spoon is made of metal, a conductor, which allows the heat to move easily to your hand. The Styrofoam is an insulator, so the heat does not transfer to your hand easily.

Radiation vs. Conduction

1. Energy that travels as waves through space between things

2. Direct contact not necessary

3. From the Sun and light

4. Can travel through empty space

1. Energy that travels through contact of things

2. Contact is necessary

3. From faster moving molecules

4. Can’t travel through empty space

Conduction in aluminum

Hot WaterMetal bar

Conduction in aluminum

Hot WaterMetal bar

Conduction in steel

Hot WaterMetal bar

Conduction

Conduction is when energy transfers from one place to another by direct contact

Differential conduction is when energy transfers at different rates depending upon the material it is passing through

Steel

Aluminum

Styrofoam

Marble

Wood

Conduction in styrofoam

Hot WaterStyrofoam Block

Differential conduction can explain these two mysteries

about the “Amazing Melting Ice Blocks”

1. Why does one block feel cold and one feel warm when they are the same temperature?

2. Why does the block that feels cold so much better at melting the ice than the “warm” block?

Convection

Transfer of heat through a liquid or gas through moving currents, called convection currents.

The cause of wind and weather.

The movement of a substance that is caused by differences in temperature and density.

EXAMPLES: wind boiling water

NATURE WANTS

EVERYTHING TO BALANCE ! !

Convection