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Chapter 10 Section 4. CONTROLLING HEAT. 10.4 Controlling Heat. Thermal Conduction. Thermal Conduction – the process by which energy is transferred as heat through a material between two points at different temperatures. T E
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Chapter 10 Section 4 CONTROLLING HEAT
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.
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
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.
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)
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
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-dash or 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.