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Energy

Energy. I. Energy and Work (p.124-131) Energy Work Conservation of Energy. THERMAL. The ability to cause change. MECHANICAL. NUCLEAR. ELECTRICAL. CHEMICAL. joules (J). A. Energy. internal motion of particles. ENERGY. motion of objects. changes in the nucleus.

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Energy

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  1. Energy I. Energy and Work (p.124-131) Energy Work Conservation of Energy

  2. THERMAL The ability to cause change. MECHANICAL NUCLEAR ELECTRICAL CHEMICAL joules (J) A. Energy internal motion of particles ENERGY motion of objects changes in the nucleus motion of electric charges bonding of atoms

  3. Which has the most KE? • Which has the least KE? 80 km/h 50 km/h 80 km/h A. Energy • Kinetic Energy (KE) • energy in the form of motion • depends on mass and velocity 80 km/h truck 50 km/h motorcycle

  4. A. Energy • Potential Energy (PE) • stored energy • depends on position or configuration of an object • Which boulder has greater gravitational PE? • What other ways can an object store energy?

  5. B. Work • Work • transfer of energy through motion • force exerted through a distance W = Fd W: work (J) F: force (N) d: distance (m) 1 J = 1 N·m Distance must be in direction of force!

  6. W d F B. Work • Brett’s backpack weighs 30 N. How much work is done on the backpack when he lifts it 1.5 m from the floor to his back? GIVEN: F = 30 N d = 1.5 m W = ? WORK: W = F·d W = (30 N)(1.5 m) W = 45 J

  7. W d F B. Work • A dancer lifts a 40 kg ballerina 1.4 m in the air and walks forward 2.2 m. How much work is done on the ballerina during and after the lift? GIVEN: m = 40 kg d = 1.4 m - during d = 2.2 m - after W = ? WORK: W = F·d F = m·a F =(40kg)(9.8m/s2)=392 N W = (392 N)(1.4 m) W = 549 J during lift No work after lift. “d” is not in the direction of the force.

  8. C. Conservation of Energy • Law of Conservation of Energy • Energy may change forms, but it cannot be created or destroyed under ordinary conditions. • EX: • PE  KE • mechanical  thermal • chemical  thermal

  9. Kinetic and potential energy conversions • Describe the energy conversions in this picture: • At the top: • ¼ of the way down: • ½ way down: • ¾ down • At the bottom: • Is the sum of KE + PE a constant? All PE, no KE 3/4 PE, 1/4 KE 1/2 PE, 1/2 KE 1/4 PE, 3/4 KE No PE, All KE Yes! It’s always 10,000 J in this case.

  10. Where are PE and KE maximums in this picture? PE and KE Max PE no KE Max KE No PE Max PE No KE

  11. C. Conservation of Energy PE  KE View roller coaster animation.

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