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Energy Chapter 11 p.285 - 301 11.1 – Forms of energy Energy is defined as the ability to do work. • Heat energy (movement of molecules) ▫ It is the sum of the kinetic energy of an object's molecules. • Electrical energy (movement of electrons) ▫ That is kinetic energy. The voltage in an electrical circuit is the potential energy that can start electrons moving. Electrical forces cause the movement to occur. • Chemical energy (potential energy until the chemical reaction puts atoms and molecules in motion) ▫ Heat energy (KE) is often the result of a chemical reaction. • Light energy (movement of waves and/or light particles called photons) ▫ It is usually formed when atoms gain so much kinetic energy from being heated that they give off radiation. This is often from electrons jumping orbits and emitting moving photons. • Nuclear energy (internal forces in the nucleus) ▫ When that potential energy is released, the result is kinetic energy in the form of rapidly moving particles, heat and radiation. Kinetic vs Potential • There are many different forms of energy, but the two main types are kinetic (energy of motion) and potential (energy of position) • KE = ½ m v2 • PE = m g h (h is height, in meters) • All previous forms of energy can be separated or defined by potential and kinetic energy. Practice • P.287 #1-3 • P.291 #4-8 • 11.1 section review #10-13 11.2 Conservation of Energy • In a closed, isolated system energy can be neither created nor destroyed. • Energy of a system = PE + KE KE = PE • Read on p.294 about roller coasters, skiing, and pendulums • Practice p.297 #15-18 Elastic collisions • Super-elastic ▫ Kinetic energy is larger after the collision Ex. an explosion • Elastic ▫ Kinetic energy is conserved Ex. atomic or nuclear particles with similar charges, magnets with similar poles facing each other, SuperBall (like ‘Flubber’). Ball bearings, a well inflated basketball, or any ball that bounces some is mostly elastic, but not completely. Inelastic collisions • Inelastic ▫ Kinetic energy is smaller after the collision Ex. An under-inflated basketball, or any ball that doesn't bounce much • Completely inelastic ▫ Kinetic energy is smaller, and the objects stick together, after the collision. Ex. A block of soft clay dropped onto a hard floor, A bad car accident where the cars stick together, Two train cars collide and stick together. Energy vs Momentum • MOMENTUM IS ALWAYS CONSERVED • Energy is only conserved in an elastic collision. • When working problems, if the collision is inelastic, SOLVE USING MOMENTUM. ▫ If energy is not conserved, there will be less energy after the collision than before. • If the collision is elastic, you may use kinetic energy to solve. Practice • P.300 #19-21 • 11.2 Section review #24-28 Assignment • Complete the second section of your Work, Power, and Energy worksheet ▫ (Kinetic Energy and Potential Energy; #1-29) Chapter Reviews • Chapter 10 review ▫ P.278-282 (#34-70 even, 79-85 all) Extra credit: #89-93 • Chapter 11 review ▫ P.306-309 (#30, 33-41 all, 54-82 even) • Due by the end of class Thursday 3/17 • Test will be Monday 3/21