Sections 9.7 and 9.8

1. Sections 9.7 and 9.8 • Specific Heat Capacity and Thermal Expansion

2. Objectives • By the end of today, you will be able to: • define and explain specific heat capacity • define and explain thermal expansion • PS - F-11, 15, and 17

3. 9.7 - Specific Heat Capacity • Different substances have different capacities for storing thermal energy. • When you heat a pot of water on a stove, it takes about 15 minutes to bring it to a boil • An equal amount of iron, it only takes about 2 minutes to raise it through the same temperature range • For silver, it would only take about a minute

4. 9.7 - Specific Heat Capacity • As you can see, different materials require different amounts of thermal energy to raise temperature. • This is because different materials absorb energy in different ways. • This is called an object’s specificheat capacity - • The specific heat capacity of any substance is defined as the quantity of heat required to change the temperature of a unit mass (g or kg) of the substance by 1 degree

5. 9.7 - Specific Heat Capacity • Consider the difference between touching an empty iron skillet that has been placed on a hot stove for one minute and touching the same skillet filled with water. • What would happen?

6. 9.7 - Specific Heat Capacity • You could safely place your hand in the water filled skillet even if it were on the stove for several minutes! • Why? • Water has a very high specific heat capacity, and therefore, it requires much more thermal energy (heat) to change its temperature!

7. 9.7 Specific Heat Capacity • Because of water’s high specific heat, it absorbs large amounts of heat for small changes in temperature. It also takes longer to cool. • In fact, this property of water changes the world’s climate. • Areas that are near, or are surrounded by, water have much smaller ranges in temperature • The water warms, or cools, the air as it blows over it, which, then, blows onto the land, thus affecting the temperature.

8. 9.8 - Thermal Expansion • What is happening to the molecules in a hot substance? • They are moving faster and moving farther apart. • The result of this is called thermal expansion.

9. 9.8 - Thermal Expansion • Most substances expand when heated and contract when cooled. • Liquids expand more than solids with increases in temperature. • These changes aren’t always noticeable ...

10. 9.8 - Thermal Expansion • . . . . But sometimes they are!

11. 9.8 - Thermal Expansion • Telephone wires are longer and sag more on hot summer days • Railroad Tracks can expand and buckle in the summer. • Pouring hot water over the lid of a jar that is difficult to open.

12. 9.8 - Thermal Expansion • Thermal expansion must be taken into account when building structures and devices. • Like the expansion joints on a bridge

13. 9.8 - Thermal Expansion • Water behaves a little differently than most substances. • Water initially (between 0° C and 4° C) expands when cooled and contracts when heated. • (This is due to the crystal structure of ice)

14. 9.8 - Thermal Expansion

15. Vocabulary Quiz Terms • thermal energy, temperature, absolute zero, heat, joule, calorie, thermodynamics, specific heat capacity, thermal expansion