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 slowlyThermal energy results in several different kinds of motion:1) kinetic energy (KE = 1/2mv^2)2) rotation energy3) vibration energy- temp is proportional to average kinetic energy, temp is not affected by rotation orvibration 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, stayscooler; 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
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