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Thermal Energy

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  1. Thermal Energy Internal energy: total amount of the energy of the particles that compose matter

  2. What is the difference between heat, temperature and thermal energy? • Heat: the quantity of thermal energy transferred from a hotter to a colder object • Temperature: the measure of the average kinetic energy of the vibrating particles that compose an object • Thermal energy: the total amount of internal energy possessed by the particles that compose matter

  3. When matter gets warmer, the atoms or molecules in the matter move faster.

  4. All matter—solid, liquid, and gas—is composed of continually jiggling atoms or molecules, which have KE.

  5. 21.1Temperature The higher the temperature of a substance, the faster the motion of its molecules. This is also referred to as the Kinetic Theory— • all matter is made of atoms and molecules that are moving. • The higher the temperature, the faster the particles move. • Given the same temperature, heavier particles move slower than lighter particles.

  6. 21.1Temperature • Measure temperature by showing expansion and contraction of a liquid in a glass tube. • Three Scales (, Fahrenheit, Celsius and Kelvin) • Fahrenheit (32-212 F) • Celsius (0-100 C) • Kelvin is a universal scale with no upper limit. (0 K or absolute zero to …)

  7. 21.1Temperature This thermometer measures temperature on both Fahrenheit and Celsius scales. Puzzler K = C + 273 Which is hotter, 500 K or 500 C? 500 C, because 500 C is 773 K 273 K

  8. 21.1Temperature • Which has more thermal energy, a cup of boiling water or Lake Michigan in winter? Lake Michigan! The water molecules are moving faster in the boiling cup of water, but there are vastly more water molecules in Lake Michigan. Are the water molecules in an ice cube moving? Yes. Motion of molecules stops at absolute zero.

  9. 21.1Temperature What is the relationship between the temperature of a substance and the speed of its molecules? The higher the temperature of a substance, the faster is the motion of its molecules and the greater their average KE.

  10. Physics and Particles • Particle is a general term used to describe molecules, atoms and sub-atomic particles

  11. Matter is changing state solid Increasing Avg. KE Increasing Temp. Particle speed is increasing melting freezing liquid evaporation condensation gas

  12. 21.1Temperature Temperature and Kinetic Energy Temperature is related to the average kinetic energy of the atoms and molecules in a substance. The faster the molecules move, the ______________ the temperature and the _____________ the average kinetic energy and the __________ the particle speed. higher greater greater

  13. 21.2Heat • Heat is the quantity of thermal energy transferred from a hotter to a colder substance. • Heat always flows from a substance with a higher temperature to a substance with a lower temperature. • Heat flows only when there is a difference in temperature. • Heat units are calories or joules.

  14. hotter 21.2Heat Entropy! Flow from higher to lower energy state. Just as water will not flow uphill by itself, regardless of the relative amounts of water in the reservoirs, heat will not flow from a cooler substance into a hotter substance by itself. colder

  15. 21.2Heat What causes heat to flow? A difference in temperature between objects in thermal contact.

  16. 21.4Internal Energy When a substance takes in or gives off heat, its internal energy changes.

  17. 21.3Thermal Equilibrium What happens when a warmer substance comes in contact with a cooler substance? • Heat flows between two objects of different temperature until they have the same temperature. (2nd law of thermodynamics) • The loss of thermal energy from the warmer object equals the gain of thermal energy for the cooler object

  18. 21.8Thermal Expansion Most forms of matter—solids, liquids, and gases—expand when they are heated and contract when they are cooled.

  19. 21.8Thermal Expansion • When the temperature of a substance is increased, its molecules jiggle faster and normally tend to move farther apart. • This results in an expansion of the substance. • Gases generally expand or contract much more than liquids. • Liquids generally expand or contract more than solids.

  20. How does a thermometer work? The kinetic theory be used to explain expansion and contraction of materials when the temperature of the material changes. As the temperature rises, heat is transferred from the surroundings to the liquid inside the thermometer and the molecules that compose the liquid vibrate faster. This causes the liquid to expand and rise. As the temperature falls, heat is transferred away from the liquid inside to the surroundings and the molecules that compose this liquid slow down. This causes the liquid to contract.

  21. The liquid in the thermometer stops rising or falling when thermal equilibrium is reached (no more heat flow!) Air temperature = Liquid temperature

  22. 21.6Specific Heat Capacity • Do copper, clay and water have the same chemical composition? • No. Copper is composed of Cu atoms and water is composed of H2O molecules. Clay is a complex silicate. • The difference in chemical composition influences how copper, clay and water respond when heat is transferred.

  23. 21.6Specific Heat Capacity The specific heat capacity of a substance is the quantity of heat required to raise 1 g of a substance by 1 degree Celsius.

  24. 21.6Specific Heat Capacity A substance with a high specific heat capacity can absorb a large quantity of heat before it will raise in temperature (water has a high specific heat). A substance with a low specific heat requires relatively little heat to raise its temperature (copper has a low specific heat).

  25. Substances with a low specific heat (e.g., metals) need very little heat to raise temperature • Good conductors, not good absorbers, do not hold onto heat well • Substances with a high specific heat need a large quantity of heat to raise temperature. • Poor conductors, good absorbers, store and hold onto heat well

  26. 21.6Specific Heat Capacity highest lowest

  27. 21.6Specific Heat Capacity think! Which has a higher specific heat capacity—water or sand? Explain.

  28. 21.6Specific Heat Capacity think! Which has a higher specific heat capacity—water or sand? Explain. Answer: Water has a greater heat capacity than sand. Water is much slower to warm in the hot sun and slower to cool at night. Sand’s low heat capacity, shown by how quickly it warms in the morning and how quickly it cools at night, affects local climates. Good conductors have a low specific heat capacity!

  29. 21.6Specific Heat Capacity A gram of water requires 1 calorie of energy to raise the temperature 1°C. It takes only about one eighth as much energy to raise the temperature of a gram of iron by the same amount. The capacity of a substance to store heat depends on its chemical composition.

  30. In winter -Heat loss from inside (warmer) to outside (colder) -Heating system must operate to transfer thermal energy from fuel to fluid to room to keep house warm In summer -Heat gain from outside (warmer) to inside (cooler) - Cooling system must operate to transfer incoming heat entering the house back to the outside Winter Vs. Summer Heat Flow

  31. Why do we need heating systems? • What do the green arrows represent? • How does this heat flow affect the temperature of the air inside the home? • Where does the energy come from that increases the temperature of the air inside the home?

  32. Explain why the heat flow for a home is different in the winter vs. the summer.

  33. 22.2Convection • Convection currents are produced by uneven heating. • During the day, the land is warmer than the air, and a sea breeze results.

  34. 22.2Convection • Convection currents are produced by uneven heating. • During the day, the land is warmer than the air, and a sea breeze results. • At night, the land is cooler than the water, so the air flows in the other direction.

  35. Generation of Sea Breezes Day Convection Air above the sea remains cooler and moves on land to replace the land air that rose Air above the land heats more rapidly and rises Sea breeze • Land • low specific heat • heat and cools rapidly • less resistant to temperature change • Sea • high specific heat • heats and cools slowly • more resistant to temperature change

  36. Generation of Sea Breezes Night Air above the ground is cooler than the air above the water and moves over the sea to replace the sea air that rose Air above the water is warmer than the air above the land and rises Land Breeze • Land • low specific heat • heat and cools rapidly • less resistant to temperature change • Sea • high specific heat • heats and cools slowly • more resistant to temperature change

  37. Generation of Sea Breezes

  38. 21.7The High Specific Heat Capacity of Water The property of water to resist changes in temperature improves the climate in many places.

  39. 21.7The High Specific Heat Capacity of Water Water has a high specific heat and is transparent, so it takes more energy to heat up than land does.

  40. Moderating Effect of Water • During the summer, surrounding air is cooled by the water and keeps the coast cooler than the intercontinental locations. • During the winter, the surrounding air is warmed by the water and keeps the coast warmer than the intercontinental locations.

  41. 21.7The High Specific Heat Capacity of Water Water’s capacity to store heat affects the global climate. Water stores and hold heat well because of its high specific heat. Gulf Stream brings warm water northeast from the Caribbean.

  42. The Gulf Stream (warm water from equator) meets The Labrador Current (cold water from polar region) Thermal Front Labrador Current Gulf Stream

  43. 21.7The High Specific Heat Capacity of Water Climate of Europe Look at a world globe and notice the high latitude of Europe. Both Europe and Canada get about the same amount of the sun’s energy per square kilometer.

  44. Marine Climate Continental Climate Cork Edmonton Same insolation angle, different climate due to proximity to water and the warming effect from the Gulf Stream http://www.sampleireland.com/weather-in-ireland-year-round.html

  45. The Gulf Stream brings warm winters to Ireland and the prevailing winds off the Atlantic carry with them rain. It means grass can grow almost all year round — creating the lush sweeping pastures of the Emerald Isle. Today they make up 93 percent of all farmland. No other country in Europe has quite as much grass as Ireland.

  46. 21.7The High Specific Heat Capacity of Water Climate of America • On the west coast, air moves from the Pacific Ocean to the land. • In winter, the water warms the air that moves over it and warms the western coastal regions of North America. • In summer, the water cools the air and the western coastal regions are cooled. The central interior of a large continent usually experiences extremes of temperature. Land, with a lower specific heat capacity, gets hot in summer but cools rapidly in winter.

  47. Reason for the Seasons 2 Changing Angle of Sunlight • The hemisphere tilted toward the Sun receives sunlight at higher angles than the hemisphere tilted away from the Sun. • Higher insolation angle means greater intensity of radiant energy (the sun shines more directly on a smaller area). Summer in Northern Hemisphere