Matter and Energy

1. Matter and Energy Continuing Heat Transfer • Heat Conduction • Convection • Radiation

2. Key Question: How does heat pass through different materials? Heat Conduction

3. Heat Transfer • There are three ways heat transfer works: conduction, convection, and radiation. • Heat flow depends on the temperature difference.

4. Thermal Equilibrium • Two bodies are in thermal equilibrium with each other when they have the same temperature. • In nature, heat alwaysflows from hot to cold until thermal equilibrium is reached.

5. Heat Conduction • Conduction is the transfer of heat through materials by the direct contact of solid matter. • Dense metals like copper and aluminum are very good thermal conductors.

6. Heat Conduction • A thermal insulator is a material that conducts heat poorly. • Heat flows very slowly through the plastic so that the temperature of your hand does not rise very much.

7. Heat Conduction • Styrofoam gets its insulating ability by trapping spaces of air in bubbles. • Solids usually are better heat conductors than liquids, and liquids are better conductors than gases.

8. Thermal Conductivity • The thermal conductivity of a material describes how well the material conducts heat.

9. Thermal Conductivity • Heat conduction in solids and liquids works by transferring energy through bonds between atoms or molecules.

10. Specific Heat • Have you ever stepped from a concrete sidewalk onto an asphalt street and noticed that the street was much warmer than the sidewalk? • If they are both receiving the same amount of sunlight then why would the asphalt be at a higher temperature? • Answer: specific heat

11. Specific Heat: the ability of a substance to absorb heat energy; how much heat is necessary to change a substance’s temp. • The concrete would have a higher specific heat than the asphalt because it takes more energy to raise its temperature • The higher the specific heat, the more heat (energy) it takes to raise its temperature

12. Which one has the higher specific heat?

13. Specific Heat • You can calculate the specific heat of a substance if you know the heat gained or lost, the mass, and the change in temperature Heat Gained Or Lost = (mass)(specific heat)(change in temp) Q=mcp T

14. I know….You’re excited about another formula!!!

15. Convection • Convection is the transfer of heat by the motion of liquids and gases. • Convection in a gas occurs because gas expands when heated. • Convection occurs because currents flow when hot gas rises and cool gas sink. • Convection in liquids also occurs because of differences in density.

16. Specific Heat of Water • Water has a high specific heat capacity; that means that it takes a long time to heat up/cool down • This is why lakes and oceans do not change temperature quickly and why the temperature near large bodies of water do not fluctuate much • People that live near the ocean have temperate weather-it doesn’t change much

17. Freezing Water • As it freezes, ice floats to the top of water, insulating the water below it. • This is why fish do not freeze in a pond or lake during the winter.

18. Lobster Anyone? • If you want a “happy” lobster for dinner, how do you cook him?

19. Key Question: Can moving matter carry thermal energy? Convection

20. Convection and Sea Breezes • On a smaller scale near coastlines, convection is responsible for sea breezes.

21. Why is it windy at the seaside?

22. Convection Currents • Much of the Earth’s climate is regulated by giant convection currents in the ocean.

23. Key Question: How does heat from the sun get to Earth? Radiation

24. Radiation is heat transfer with NO atoms! Radiation is the transfer of heat energy through electromagnetic waves. Radiation

25. The third method of heat transfer There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. How does heat energy get from the Sun to the Earth? RADIATION ?

27. Radiation transfers heat in all directions-even down. Convection currents always rise. Radiation requires NO contact. Convection and conduction require touching. Radiation can go through transparent materials (like glass) Radiation

28. All energy on earth comes originally from the sun. Space is a vacuum (no matter at all), so only radiation can travel through space to the earth. Vacuum: A region of space that contains no matter. Heat is transferred by radiation. Vacuum

29. White colors reflect heat radiation

30. Radiation Absorption Dark objects absorb more radiation; therefore they heat up AND cool off faster than light colored objects. Dull objects absorb more radiation than shiny objects.

31. Radiation questions Why are houses painted white in hot countries? White reflects heat radiation and keeps the house cooler. Why are shiny foil blankets wrapped around marathon runners at the end of a race? The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.

32. Radiant Heat • We do not see the thermal radiation because it occurs at infrared wavelengths invisible to the human eye. • Objects glow different colors at different temperatures.

33. Radiation travels in straight lines True/False Radiation can travel through a vacuum True/False Radiation requires particles to travel True/False Radiation travels at the speed of light True/False Radiation

34. Check your Understanding