Thermal Energy. Chapter 6 2 Transferring Thermal Energy

Transcription

1 Thermal Energy Chapter 6 2 Transferring Thermal Energy

2 Objectives Compare and contrast conduction, convection, and radiation. Compare and contrast conductors and insulators. CLE Examine the applications and effects of heat energy.

3 Heat Transfer Heat flows from hot to cold. If you hold something cold, heat flows from hand to object. If you hold something hot, heat flows from object to hand

4 A. Conduction Conduction transfer of thermal E through matter by direct contact of particles. (particle to particle). Particles collide with each other.

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6 Cont. 1.Kinetic energy is transferred as particles collide. 2.Solids, particularly metals, are good heat conductors.

7 Conduction Heating of metal pan- Particles in handle of pan move slowly Fast moving particles from the bottom bump into slower particles and speed them up Occurs until all particles move the same speed 3. Conduction works best in solids- especially metals- because particles are close together. Metals- good conductors-because electrons move easily & transfer KE to nearby particles

8 Conduction Conduction occurs in all states of matter.

9 B. Convection The transfer of heat energy by the movement of heated particles in a fluid is called convection.

10 1. Fluids can be a gas or liquid any material that flows.

11 Cont. 2. Convection currents transfer heat from warmer to cooler parts of a fluid. 3. Convection is the transfer of heat by bulk movement, (a group of particles moving from one place to another.)

12 4. The heated particles move from one location to another, bringing their energy with them

13 Convection Hot water rises, cools, and falls. Heated air rises, cools, and falls.

14 Convection

15 Convection-results in changes in density As particles move faster, they get farther apart Fluid expands as temperature increases Larger volume = less density Less density results in the rise of the warmer fluid

16 Lava Lamp- Cool oil = dense = sits on the bottom Warmer oil = less dense than alcohol & rises As it rises, it loses energy through conduction Causes decrease in density = sinking

17 Oil is warm, so it rises Convection current Oil starts to lose heat and falls Conduction occurs when heat is transfered from the warm metal to the oil Radiant energy is produced by the light bulb causing the metal to warm

18 C. Radiation Radiation energy transfer by electromagnetic waves.

19 Radiation 1. Radiant energy passes through the SPACE BETWEEN particles, and is therefore, more easily passed through gases. 2. Examples include: heating your hands by a campfire, the sun heating the earth.

20 C. Radiation 3. Radiation does NOT need a state of matter to flow through.

21 4. Transfer of heat to the earth occurs through radiation. The waves travel through space even without matter

22 Radiation 5. When radiation strikes a material, some energy is absorbed, some is reflected, and some may be transmitted through the material.

23 6. Dark colors absorb radiant energy. Light colors reflect radiant energy

24 Cont. 7. Heat transfer by radiation is faster in a gas than in a liquid or solid. 8. All heat created by a light source is radiant energy.

25 Thermal energy transfer

26 Radiant Energy Energy transfer by radiation When radiation strikes Radiation a substance: Some energy is absorbed some is reflected some is transmitted through the material Amount of energy that is absorbed, reflected and transmitted depends on: Type of material Dark absorb more energy than light

27 D. How do living things control the flow of heat? Most living things control the flow of heat by using special features such as fur, blubber, or scales.

28 E. What are insulators? Insulator material that does not let heat flow through it easily.

29 Cont. 1.Gases such as air usually make better insulators than liquids or solids.

30 Cont. 2. A vacuum layer in a thermos is a good insulator because it contains almost no matter to allow conduction or convection to occur.

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32 Discussion Question 2 What state of matter generally makes a good heat conductor? Heat insulator?

33 Answer Solids generally conduct heat better than liquids or gases. Gases usually make better insulators than liquids or solids.

34 Pop QUIZ: 1. This is the transfer of heat by particles bringing their energy from one location to another. 2. This type of transfer occurs more easily through gases. 3. This is the type of heat transfer that occurs in liquids. 4. This is the transfer of heat by particles colliding with one another 5. This is the transfer of heat energy by electromagnetic waves. 6. This is the type of heat transfer that occurs in solids.

35 Objectives Compare and contrast the transfer of thermal energy by conduction, convection, and radiation. Compare and contrast conductors and insulators. CLE Examine the applications and effects of heat energy.