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Chapter 4

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  1. Chapter 4 Energy

  2. First, Review…. • http://ed.ted.com/lessons/how-does-work-work-peter-bohacek

  3. What is energy? Energy is the ability to cause change Energy is NOT matter – no mass, no volume Energy is: heat, electricity, chemical reactants

  4. Kinetic Energy • Energy of an object in motion • Includes the mass and speed of the object m X v2

  5. Practice • A baseball with a mass of 0.15 kg is moving at a speed of 40 m/s. What is the baseball’s kinetic energy?

  6. Potential Energy • Potential energy is stored in an object. • An object’s potential to do work

  7. How is energy stored? • Elastic potential energy – stored by something that can stretch or compress • Rubber band • Slinky • slingshot

  8. How is energy stored? • Chemical Potential Energy – energy stored in chemical bonds • Food • A match • gasoline

  9. How is energy stored? • Gravitational Potential Energy (GPE)– energy of an object due to it’s position above the Earth • An apple on a tree • A roller coaster at the top of a hill • A projectile at the top of it’s curve • Anything that’s about to fall • GPE changes as an object is higher in the air

  10. How does a roller coaster work? • http://www.youtube.com/watch?v=-dpBVtAbKJU

  11. Gravitational Potential Energy • GPE: gravitational potential energy • m: mass • g: acceleration due to gravity (9.8 m/s2) • h: height

  12. Practice 2. A rock climber is 200m above the ground and has a GPE of 117,600 J. What is the rock climber’s mass?

  13. Section 2 – Conservation of Energy The law of conservation of energy- • Energy can change from one form to another but the total amount of energy never changes • Energy in = Energy out

  14. What forms does energy take? • Electrical energy – transferred through the flow of electrons through a conductor • Chemical energy – transferred by forming or breaking molecular bonds • Mechanical Energy – transferred between potential & kinetic energy • Radiant energy – transferred via electromagnetic waves (light, heat, sound..)

  15. What types of energy transformations occur around us? • Electrical to Radiant – electricity transforms to radiant heat and light energy in a lamp • Other examples: • __________________ • __________________ • __________________

  16. What types of energy transformations occur around us? • Chemical to mechanical – fuel combustion converts chemical energy to kinetic energy when a car moves Other examples: • ___________________ • ___________________ • ___________________

  17. Conversions Between Kinetic and Potential Energy • All work involves conversions between potential and kinetic energy Mechanical energy = potential energy + kinetic energy

  18. Falling Objects mv2 mv2

  19. Converting Mass to Energy Mass is converted to energy in nuclear fusion and nuclear fission • Nuclear Fission – atoms are broken apart to release energy • Example: nuclear power plants • Nuclear Fusion – atoms combine to release energy • Example: the sun

  20. Atomic Bomb – Hiroshima & Nagasaki, Japan 1945

  21. Converting mass to energy • Just how small is an atom? • Inside a nuclear reactor core