1. Sec. 3 Temperature & Thermal Energy
Ch. 9 Energy
Sec. 3
Temperature & Thermal Energy

2. Reminder…
molecules are constantly in motion & thus, have kinetic energy
not all molecules move at the same speed

3. Expansion and Contraction
Almost all substances…
expand when heated
b/c molecules speed up & move apart
contract when cooled
b/c molecules slow down & move closer
Depends on 2 main things:
amount of temp. change
more temp. change = more expansion/contraction
state of the material
liquids expand/contract more than solids

4. Temperature
temperature - average kinetic energy of all molecules in a substance
molecules w/ faster motion = more kinetic energy = higher temp.

5. Measuring Temperature
thermometer - device used to measure temp.
measures expansion of a liquid in a tube
2 Common Temp. Scales:
Fahrenheit - used in U.S. and Canada - water freezes at 32° & boils at 212°
Celsius - used outside North America - water freezes at 0° & boils at 100°  
Note: 1 Celsius degree is bigger than 1 Fahrenheit degree (thus 50° C is warmer than 50° F)

6. Converting Fahrenheit and Celsius
°F to °C °𝑪= 𝟓 𝟗 (°𝑭−𝟑𝟐) °C to °F °𝑭= 𝟗 𝟓 °𝑪+𝟑𝟐

7. Kelvin 𝑲= °𝑪+𝟐𝟕𝟑 °𝑪=𝑲−𝟐𝟕𝟑 Converting Celsius & Kelvin…
Kelvin - another temp. scale where the lowest possible temp. is 0 K (absolute zero) – only used in science labs
Converting Celsius & Kelvin…
°C to K
𝑲= °𝑪+𝟐𝟕𝟑
K to °C
°𝑪=𝑲−𝟐𝟕𝟑

8. Thermal Energy
thermal energy - the TOTAL kinetic energy all molecules in an object
more molecules = more thermal energy
moves from warmer to cooler objects
dependent on size (b/c it’s a total)

9. Temperature & Thermal Energy
temp. & thermal energy are different!
temp. is based on AVERAGE kinetic energy
thermal energy is based on TOTAL kinetic energy
EXAMPLE
2 glasses of milk have the same temp. - when both glasses are poured into a pitcher the temp. stays the same BUT the thermal energy increases b/c there are more molecules