Chapter 21 Thermal Energy

1. Chapter 21 Thermal Energy

2. Section 1 Temperature and Thermal Energy • Temperature is…. • How much heat something has or does not have. • Measure of the average amount of kinetic energy in the molecules of a substance • Kinetic energy = movement = heat • The higher the temp. the faster the molecules move.

3. Thermal Energy • The sum of the kinetic and potential energy in molecules • Kinetic = energy of motion • Potential = energy stored in bonds • Increases when: • Number of bonds or molecules increase • Motion of molecules increase • Space decreases

4. Thermal Expansion • Almost all substance will expand when heated and contract when cooled. • Why? • Gases expand more than liquids and liquids expand more than solids. • Marshmallow in microwave

5. Temperature scales • Celsius • Fahrenheit • Kelvin

6. Conversions • Fahrenheit to Celsius • (° F – 32) * 5/9 • Celsius to Fahrenheit • (° C * 9/5) + 32 • Celsius to Kelvin • K = ° C + 273

7. Homework – convert! • Fahrenheit to Celsius: • 32 • 212 • 80 • 55 • 72 • Celsius to Fahrenheit: • 0 • 100 • 14 • 27 • 33 • Convert to Kelvin: • 0c • 100c • 44c • 72F • 11F

9. Complete the flow chart.

10. Homework • Convert 31° F to Kelvin • Convert 250 K to Celsius. • Convert 320 K to Fahrenheit.

11. Section 2 Heat • Kinetic energy that is transferred from the molecules of one object to another. • + =

12. 3 ways heat is transferred • Conduction • Heat transfer by direct contact • Kinetic energy of molecules transfers from moving particles to slower moving particles • Hot chocolate on your tongue • Ice cube in your hand • Egg in a skillet.

13. Radiation • Heat is transferred electromagnetic waves • Waves carry energy • How the sun heats the earth. • Heat you feel from a camp fire. • How food is heated in a microWAVE.

14. Convection • Heat is transferred by molecules moving from one area to another in a gas or liquid • When boiling water for Mac and Cheese. • Turn stove on and burner transfers heat to pot through conduction. • Heat transfers from pot to first water molecules through conduction. • Water molecules on the bottom that have heat move to the top and the entire pot of water is heated by convection. • Macaroni is heated through conduction.

15. Natural Convection • Swimming pools and lakes. • Warmer water is always on top. • Wind • Created by cool dense air pushing it’s way toward warmer less dense air. • Why the ocean is a great place to fly a kite.

16. Thermal conductors • Any material that easily transfers heat. • Can you name a few? • Metals • Gold • Copper • Iron • Titanium

17. Thermal insulators • A material that heat does not flow easily. • Used to handle hot objects or insulate houses and buildings. • Wood • Fiberglass • Plastic • Rubber • Air

18. Thermal Absorption • Different materials absorb heat at different rates. • On a hot summer day would you rather stand barefoot for an hour on a paved parking lot surface or on the grass? • Parking lot absorbs and retains heat.

19. Thermal pollution • The increase in the overall temperature of a body of water due to warm water inflow. • Plants and factories that sit on the banks of a river use the water to cool their machines and then release the warmed water back into the natural environment. • Effects = • warm water can retain less oxygen than cool water. Aquatic life needs oxygen.

20. Assignment. 10 pts. • Find an article on thermal pollution caused by human activity. • Write a short paragraph explaining the impacts on the environment and how we as humans could fix the problem. • Design an energy efficient house. Label all areas where radiation, conduction, and convection will take place. Make sure to put a (+) beside those areas that are good for energy use and a (-) beside areas where the heat transfer is bad.