Lecture 3 why do is energy use so inefficient Why do we have so much wasted energy It s because of the laws of physics thermal energy the random motion of atoms molecules not ordered motion we can add thermal energy to matter in various ways by releasing internal potential energy often burning usually chemical moving heat through convection moving hot masses conduction atomic colli sions or radiation we emit thermal radiation can be seen with infrared detection if it s a cold winter day and you re in an unheated cabin you will feel warmer standing in front of a full length mirror because the mirror reflects your own thermal ra diation back at you so you lose heat more slowly Thermal energy results in several different kinds of motion 1 2 3 kinetic energy KE 1 2mv 2 rotation energy vibration energy temp is proportional to average kinetic energy temp is not affected by rotation or vibration of atoms or molecules if we add thermal energy temp rises remove thermal energy temp drops ex cept in cases like dihydrogen oxide water thermal expansion if temp increases material expands and the distance be tween atoms or molecules gets larger St George Island Bridge 4 mi long difference of 10 ft between its hottest and coldest temps thermal expansion joints like laced fin gers can slide open or closed to account for thermal expansion cracking concrete caused by thermal expansion grooves in a sidewalk are put there so crack happens in the groove and isn t noticeable New Orleans levees broke because the expansion joints were too weak to with stand the flood which part of a welding flame is the hottest the blue part emission and absorption are affected by the surface of the object Emission if the surface is shiny or white it emits poorly and stays hotter if the surface is dark or black it emits fast and gets cooler faster Absorption if the surface is shiny or white it reflects a lot and absorbs little stays cooler if the surface is dark or black its absorbs a lot and reflects little gets hotter Sea Breezes in the day the shore is hotter and the ocean is cooler cool breezes come off the ocean toward us pushed by warm breezes going out to cooler air at sea at night shore is cooler and ocean air is warmer warm ocean air migrates to cooler land air our cool breeze migrates out to warm sea air light bulbs are made of a Tungsten double spiral filament and power wires
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