Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Important forms of energy How energy can be transformed and transferred Definition of work Concepts of kinetic, potential, and thermal energy The law of conservation of energy Elastic collisions Chapter 10 Energy Topics: Sample question: When flexible poles became available for pole vaulting, athletes were able to clear much higher bars. How can we explain this using energy concepts? Slide 10-1

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 10-3

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 10-4

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Forms of Energy Mechanical Energy Thermal Energy Other forms include Slide 10-12

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Basic Energy Model Slide 10-13

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy Transformations Kinetic energy K = energy of motion Potential energy U = energy of position Thermal energy E th = energy associated with temperature System energy E = K + U + E th + E chem +... Energy can be transformed within the system without loss. Energy is a property of a system. Slide 10-14

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Some Energy Transformations E chem  U g K  E th E chem  U g U s  K  U g Slide 10-15

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy Transfers These change the energy of the system. Interactions with the environment. Work is the mechanical transfer of energy to or from a system via pushes and pulls. Slide 10-20

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy Transfers: Work W  KW  E th W  U s Slide 10-21

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Law of Conservation of Energy Slide 10-23

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Basic Equation K f  U f   E th  K i  U i +  E sys A few things to note:  E sys can be positive (Energy in) or negative (Energy out) We are, for now, ignoring heat. Thermal energy is…special. When energy changes to thermal energy, this change is irreversible. Slide 10-24

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy Model Types of Energy Kinetic Energy KE = 1/2 mv 2 Potential Energy: Gravitational Potential Energy PE g = mgy Spring Potential Energy Pe s = 1/2 k  L 2 Conservation of Energy (Closed System) Visualizations: Energy Bar Charts

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Checking Understanding A skier is moving down a slope at a constant speed. What energy transformation is taking place? Slide A. E K => E g B. E g => E th C. E s => E g D. E g => E K E. E K => E th

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. A skier is moving down a slope at a constant speed. What energy transformation is taking place? B. Slide Answer

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy Bar Charts for a swinging pendulum Slide 10-7 Demonstration: Smash the Professor - Part 2

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 10-7 Examples of Energy Bar Charts & solving Energy Problems

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy Bar Charts and Energy Transformations For the following questions, start by drawing energy bar graphs and identifying energy transformations. Then answer the question. 1.A block slides down a frictionless ramp of height h. It reaches velocity v at the bottom. To reach a velocity of 2v, the block would need to slide down a ramp of height A h B. 2 h C. 3 h D. 4 h E. 6 h Slide 10-23

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy Bar Charts and Energy Transformations For the following questions, start by drawing energy bar graphs and identifying energy transformations. Then answer the question. 2.A block is shot up a frictionless 40 degree slope with initial veloctiy v. It reaches height h before sliding back down. The same block is shot with the same velocity up a frictionless 20 degree slope. On this slope, the block reaches height A. 2 h B. h C. 1/2 h D. Greater than h, but I connot predict an exact value. E. Less than h, but I can't predict an exact value Slide 10-23

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy Bar Charts and Energy Transformations For the following questions, start by drawing energy bar graphs and identifying energy transformations. Then answer the question. 3.Two balls, one twice as heavy as the other, are dropped from the roof of a building. Just before hitting the ground, the heavier ball has _________ the kinetic energy of the lighter ball. A. one-half B. the same amount as C. twice D. four times Slide 10-23

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Conceptual Example Problem A car sits at rest at the top of a hill. A small push sends it rolling down a hill. After its height has dropped by 5.0 m, it is moving at a good clip. Write down the equation for conservation of energy, noting the choice of system, the initial and final states, and what energy transformation has taken place. Slide 10-25

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Example: Roller Coaster Demonstration: which ball reaches the end of the track first A. The one in front B. The one in back C. Neither, they both reach the end of the track at the same time Using Conservation of Energy to find the speed of a roller coaster Slide 10-23