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Chapter 14: Thermal Energy & Heat

Chapter 14: Thermal Energy & Heat. Introduction. Heat is the transfer of thermal energy. Topics of Discussion. Temperature and Thermal Energy (Section1) The Nature of Heat (Section 2) Thermal Energy and States of Matter (section 3) Uses of Heat (Section 4).

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Chapter 14: Thermal Energy & Heat

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  1. Chapter 14: Thermal Energy & Heat

  2. Introduction • Heat is the transfer of thermal energy.

  3. Topics of Discussion • Temperature and Thermal Energy (Section1) • The Nature of Heat (Section 2) • Thermal Energy and States of Matter (section 3) • Uses of Heat (Section 4)

  4. TEMPERATURE and THERMAL ENERGY(Section one) • Temperature is the measure of the average kinetic energy of the individual particles in an object. • Three common Temperature scales for measuring temperature • Fahrenheit • Celcius • Kelvin

  5. Fahrenheit • U.S. System • Water Freezes at 32o • Water Boils at 212o • 180 equal intervals between freezing and boiling called degrees Fahrenheit (oF) • Absolute zero is -460o

  6. Absolute Zero • Absolute zero is the lowest temperature possible. • At this temperature, no more energy can be removed from matter. • -460oF • -273oC • 0 K

  7. Celcius Scale • This system is used in most of the world. • Water Freezes at 0o • Water Boils at 100o • 100 equal intervals between freezing and boiling called degrees Celcius (oC) • Absolute zero is -273o

  8. Kelvin Scale • This system is used most in physical science. • The Kelvin scale is defined so that zero is absolute zero. • Units on the Kelvin scale are the same size as those in Celcius – called kelvins (K) • Water Freezes at 273o • Water Boils at 373o • Absolute zero is 0o

  9. Thermal Energy • Temperature is a measure of the average kinetic energy of the individual particles of matter. • Thermal energy is the total energy of all of the particles.

  10. The Nature of Heat(Section 2) • Heat is thermal energy moving from a warmer object to a cooler object. (Only = One way.) • Heat is transferred by: • Conduction, • Convection, and • Radiation.

  11. Conduction • Heat is transferred from one particle of matter to another without the movement of matter itself. • Ex: A pot heating on a stove. The fast moving (hot) particles of the element collide with the slow (cold) particles of the pot and energy is transferred.

  12. Convection • Heat is transferred by the movement of currents within a fluid (liquid or gas.) • Ex: Water heating in a pot on the stove. • Differing densities cause the water to flow in a convection current.

  13. Radiation • The transfer of energy by electromagnetic radiation. • Radiation does not require matter to transfer thermal energy. • Ex: Heat from the sun, heat lamp, and a microwave oven.

  14. Conductors and Insulators • Conductor –A material that conducts (transfers) heat well. • Ex: metal. • Insulator –A material that does not conduct heat well. • Ex: Wood, Glass and gasses.

  15. Specific Heat • Specific Heat –The amount of energy required to raise the temperature of one kilogram of a substance by 1 kelvin. • Δenergy =Mass X Specific heat X Δ temperature(Δ = change)

  16. Thermal Energy andStates of Matter(Section 3) • Three States of matter: • Solids • Liquids • Gases

  17. Solids • Ex: Ice cube & text book • Tightly packed particles • Particles in fixed position (vibrate) • Definite volume & shape

  18. Liquids • Ex: Water & Molten steel • Particles close together (further than solid) • Particles can move around • Definite volume, random shape

  19. Gases • Ex: Steam & air • Fast moving / far apart particles • Particles free to move • Random volume, random shape(Expand to fit space available)

  20. Changes of State • Change of state is the physical change from one state to another. • Matter will change from one state to another if thermal energy is absorbed or released. • Solid-Liquid • Liquid-Gas • Temperature = constant

  21. Solid – LiquidChanges of State • Melting • From solid to liquid • Thermal energy increases • Melting point = temperature at which a solid changes to liquid • Freezing • From liquid to solid • Thermal energy decreases • Freezing point = temperature at which a liquid changes to solid

  22. Liquid - GasChanges of State • Vaporization • From liquid to gas • Thermal energy increases • Boiling point = temperature at which a liquid changes to gas • Condensation • From gas to liquid • Thermal energy decreases

  23. Thermal Expansion • As thermal energy of a substance increases, its particles spread out and the substance expands. • Thermometers • Expanding liquid – Mercury or alcohol • Thermostats • Expanding bimetallic strips

  24. Uses of Heat(Section 4) • Heat Engines – convert thermal energy to mechanical energy • External Combustion Engines Fuel is burned outside the engine • Internal Combustion Engines Fuel is burned in cylinders inside the engine.

  25. Internal Combustion Engines • Gasoline and Diesel • Pistons move up and down (one stroke) to drive crankshaft • Two Stroke • Four- Stoke • Intake Stroke, Compression Stroke • Intake Stroke, Compression Stroke • Ignition • Power Stroke, and Exhaust Stroke

  26. Refrigerators • A refrigerator is a device that uses an outside energy source to transfer thermal energy from a cool area to a warm area.

  27. Key Terms

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