Energy

Energy sources Electrical energy Magnetic energy –Today we know it’s “electromagnetic” combined. Solar power (energy from light) Energy from chemical bonds –Food, coal, natural gas, biomass, incineration, etc. Energy stored in nucleus of atoms (Nuclear) And…

Los Angeles Dept. of Water & Power sources of energy (Power Content Label) Source Biomass/ waste 1% Geothermal 1%<1% 1% Hydroelectric 13%11%9%11% Solar <1% 0% Wind <1%1% 0% Coal 47%48%53%50% Natural gas 30% 26%24% Nuclear 8%10%

Southern California Edison Sources of energy (Power Content Label) Source Biomass/ waste 2% Geothermal 9% 11% Hydroelectric 7%6%4% Solar 1% Wind 3% 4% Coal 7% 14% Natural gas 51%54%44% Nuclear 20%17%20%

Energy quantities we’ll discuss in Physics 2A Energy from forcing things to move –WORK = …. Energy in moving things (Hydroelectric, wind) –KINETIC ENERGY: KE = … Energy stored by gravity (Hydroelectric, water towers) –GRAVITATIONAL POTENTIAL ENERGY. PE g = … Energy stored in stretched things –ELASTIC POTENTIAL ENERGY (SPRING P.E.) PE s = … Heat (geothermal) – CHAPTER 9… Q = …

Units of energy Calories (food we eat) calories (physics unit – heat. 1 Cal = 1000 cal) Joules (J) – most often used by physicists Kilowatt-hour (kW-hr) = Joules B.t.u. – British thermal unit Thermals – 100,000 BTUs

Can kinetic energy be negative? 1.Yes 2.No

Can spring potential energy be negative? 1.Yes 2.No

Fundamental relationships & definitions Energy is the ability to cause change (damage) We’ll focus on Mechanical Energy, which includes: KE + PE g + PE s. We’ll ignore non-mechanical energies, such as nuclear, chemical, and “internal” (atomic kinetic). Fundamental relationship: the energy of a system only changes if outside influences act on the system.  ME =  W ext + Q ext + light ext. We’ll ignore last two terms for now.

Is  KE = ½ m (v f – v i ) 2 1.False 2.True