Controlling Heat

1. Chapter 10 Section 4 Controlling Heat

2. 10.4 Controlling Heat

3. Thermal Conduction • Thermal Conduction – the process by which energy is transferred as heat through a material between two points at different temperatures. • T  E • Vibrating atoms jostle their less energetic neighbors and transfer some of their energy in the process.

4. Thermal conductors are substances that rapidly transfer thermal energy. • In general, metals • Thermal insulators are substances that slowly transfer thermal energy. • Cork, cardboard, fiberglass, gases

6. Convection and Radiation also Transfer Energy • Convection involves the displacement of hot matter in the form of a fluid by cool matter. • Natural: associated with the combined effects of pressure differences, conduction, and buoyancy. • Forced • Radiation involves the absorption or loss of electromagnetic radiation usu. in the form of infrared.

7. Examples: Natural Convection

8. Clothing and Climate • Human body: 37.0°C (98.6°F) • In extreme cold environments, person can become hypothermic. • 32.2°C (90.0°F), lose consciousness • Fatal at 25.6°C (78.0°F)

9. Insulating materials retain energy for cold climates • Air is an efficient insulator. • Inupiat Eskimo • Average Arctic air temperatures: 10°C (50°F) to −37°C (−35°F) • Traditional parka (atigi) made of caribou skin

10. Evaporation aids energy transfer in hot climates • Arabian Desert temperatures are often in excess of 38°C (100°F) • Heat exhaustion or heat stroke if body temperature gets too high. • Bedouin cloths • Dish-dashor dish-dasha • Kefiyah, and the mandil and a hatta Because of the high specific heat capacity and latent heat of vaporization for water, evaporation removes a good deal of energy from the skin and air, thus causing the skin to cool.