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Lecture on Energy Energy: -what is it? -where does it come from? -where does it go? -how do you measure it? A. energy is “the ability to do work”: to change things: in terms of position or speed or temperature etc. B. so, work is related to energy: work = force x distance W= F x D C. power is also related to energy: rate (time) work is done: power = work time The energy-work-power triangle: Energy Power Work D. the unit for energy is the Joule (J), and for work too 1. 1 joule = 1 Newton x 1 meter: energy = force x distance (same as work!!) 2. so a joule is a function of the amount of force applied for a motion. Need motion to occur for energy to be used E. E = MC2: more mass = more energy F. energy is released in thermonuclear blasts, so energy and mass are related: different forms of the same thing G. four forms of energy: 1. mechanical: due to a motion or a position examples: both kinetic and potential energy 2. chemical: stored in the bonds between atoms: food, gasoline, battery acid 3. nuclear: stored in the nucleus of all atoms, due to both their strong and weak nuclear forces: the sun is a massive nuclear rxn, releasing many different types of energy: nuclear, heat, light etc 4. radiant: pure energy from the electromagnetic spectrum: -long waves: radio, micro -short waves: x-ray, gamma -in between waves: IR, light (roygbiv), ultra violet (uv) H. law of conservation of energy: energy is not created or destroyed, only transferred, often as heat: rub hands, feel brakes/tires, paper on fire I. energy sources for Earth: 1. sun is the biggest one for Earth/humans, so much so we fight wars over it: -fossil fuels: what are they, how produced? -photosynthesis: what is it, what does it produce -water cycle: what is it/what drives it? -wind energy: how is it produced? 2. atomic: nuclear? 3. geothermal: fission w/in Earth? J. two categories of energy 1. potential energy: stored energy a. by position: ? b. as matter: mass: E = MC2 c. formula: Ep= mgh m= mass, g= accel of gravity, h= height Ep= mgh work = force x distance force = mass x accel so, potential energy is the same as work!: work = force x distance A rock, having a mass of 15.3 kg, rests at the top of a cliff, 123, 000 cm above the ground. What is the potential energy of the rock? Show your work: 2. kinetic energy: energy of motion a. depends on the mass moving, and b. depends on the velocity c. formula: Ek = 1MV2 2 d. note: the faster (velocity) an object is, has a huge effect because it is squared!! (always square the velocity first: order of operations) Jean shoots a 0.251 kilogram arrow at a tree with a kinetic energy of 10.0 J. What is the velocity with which the arrow hits the tree? PE = 100%, KE = 0% PE & KE = 50% KE = 100%, PE = 0%