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

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

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

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

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)

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

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

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)

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