HEAT TRANSFER SC Standard 6-5.5

Tuesday, January 4, 2011 Complete planner Get out a sheet of paper and entitle HEAT TRANSFER NOTES…complete header & Entry # 10 Copy TABLE on WHITEBOARD

RADIATION - thermal energy that is transferred in the form of (electromagnetic) rays or waves and can occur in solids, liquids, or gases.

Radiation (cont.) All objects emit radiation, but hot objects emit more than cool objects. The hotter the object, the more radiation it emits.

Radiation (cont.) There is NO TOUCHING of the object, you can feel the thermal energy without touching it. (emit means gives off) example: energy from the sun by rays or heat from a fire.

CONDUCTION -the direct transfer of thermal energy that occurs when molecules bump into one another when two substances are touching. When fast moving molecules (warmer object) bump into slower moving molecules (cooler object) it transfers some of it’s energy..

Conduction (cont.) The closer together the molecules in a substance are, the more effectively they can conduct heat.

Conduction (cont.) It works well in solids such as metals where the molecules are closer together (because they only have to move a short distance to bump into each other), but not as well in gases or liquids. Thermal energy ALWAYS travels from HOT to COLD! example: hot sand/pavement transferring to your feet when you walk on it, or ice melting in your hand

CONVECTION the transfer of thermal energy by the flow of gases or liquids. In gas and liquids, molecules can move much more easily than they can in a solid, as a result, the more energetic molecules can travel from one place to another, and carry their energy along with them.

Convection (cont.) example: pot of water boiling (because the molecules are farther apart in the warm water, this water is less dense than the cooler water. As a result, the warm water rises and is replaced at the bottom of the pot by cooler water.) or water in a bath tub, preheating an oven.

Heat Transfer QUIZ 1.Microwaving method 2.Warmth from a fire 3.Accidentally touching a hot light bulb 4.Sunbathing on the beach 5.Noodles boiling in a pot 6.“Nuking” your hot chocolate 7.Burning your finger as you remove it from the microwave 8.Air popping method 9.A pot sitting on a HOT stovetop eye 10.Jiffy Pop method

Condensed Heat Transfer Notes RADIATION - electromagnetic rays or waves - solids, liquids or gases - solids, liquids or gases - EMIT (to give off) - EMIT (to give off) - NO TOUCHING - NO TOUCHING EX: sun’s rays, campfire, microwave popcorn method EX: sun’s rays, campfire, microwave popcorn method

Condensed Notes (cont.) CONDUCTION - direct transfer of heat - direct transfer of heat - TOUCHING or direct contact - TOUCHING or direct contact - faster molecules = warmer temperatures - faster molecules = warmer temperatures slower molecules = cooler temperatures slower molecules = cooler temperatures - TRANSFERS HOT TO COLD - TRANSFERS HOT TO COLD - Solids = more molecules = best conductors - Solids = more molecules = best conductors EX: walking across hot pavement / sand EX: walking across hot pavement / sand touching a HOT stovetop eye touching a HOT stovetop eye Jiffy Pop popcorn Jiffy Pop popcorn

Condensed Notes (cont.) CONVECTION - gases & liquids - gases & liquids - MOVEMENT to transfer heat - MOVEMENT to transfer heat - warm air rises, cool air is lower - warm air rises, cool air is lower EX: preheating an oven EX: preheating an oven cooking noodles in boiling water cooking noodles in boiling water Air Pop popcorn Air Pop popcorn