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Writing prompt – 10/13/06

Writing prompt – 10/13/06. IN COMPLETE SENTENCES: Write down the order of changes in energy that happens when plucking a guitar string. (longest chain of energy transfers gets candy!!!!). Energy and Work!!!. They’re pretty much the same thing…. Energy.

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Writing prompt – 10/13/06

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  1. Writing prompt – 10/13/06 IN COMPLETE SENTENCES: Write down the order of changes in energy that happens when plucking a guitar string. (longest chain of energy transfers gets candy!!!!)

  2. Energy and Work!!! They’re pretty much the same thing…

  3. Energy • Definition: The ability of some physical system to do work. The units of energy and work are Joules (J) • Some different types we named • Potential • Gravitational, Spring, Chemical, Nuclear, • Kinetic • Motion, Heat, Sound (Vibration)

  4. Mechanical Energy • The big types we’ll focus on are KINETIC, GRAVITATIONAL POTENTIAL, and SPRING POTENTIAL ENERGY • These can all be listed as types MECHANICAL ENERGY

  5. Gravitational Potential Energy • What changes how much potential energy you have? • Height • Mass • So how can you increase something’s potential energy? • Increase the mass or the height

  6. Gravitational Potential Energy • How do we calculate Gravitational potential energy? • This equation: PE = mgh • m=mass, h=height, g=9.81 m/s2 • g is the acceleration of gravity, it’s CONSTANT

  7. Gravitational Potential Energy • PE = mgh • So how much energy does a 5kg ball that is held at a height of 2 meters? • PE= mgh = 5 X 2 X 9.81=98.1 J

  8. Gravitational Potential Energy • PE = mgh • How about a 10kg ball at 1m high? • PE= mgh = 10 X 1 X 9.81=98.1 J

  9. Kinetic Energy • What changes how much kinetic energy you have? • Velocity • Mass • So how can you increase something’s potential energy? • Increase the mass or the velocity of it

  10. Kinetic Energy • How do we calculate Kinetic energy? • This equation: KE = 1/2mv2 • m=mass, v=velocity • NOTE: V squared does NOT equal V x 2!!! • V squared = V x V

  11. Kinetic Energy • Practice with KE = ½ mv2 • How much kinetic energy does a runner of 40 kg running at a speed of 5 m/s have? • KE = ½ mv2 = ½ x 40 x 52 = ½ x 40 x 25 = 500 J

  12. Kinetic Energy • Practice with KE = ½ mv2 • If a ball has 200J of energy and a mass of 4kg what is its VELOCITY? • KE = ½ mv2 so… 200 = ½ x 4 x v2 • so v = square root(200/2)

  13. Conservation of Energy • Energy CANNOT be created or destroyed, it can only be CHANGED!!! • So a ball held in the air has potential energy, what does it change into as it falls? • KINETIC!!!

  14. Conservation of Energy • If a ball has 10J of potential energy before it is dropped, how many joules of kinetic energy does it have at the bottom of its fall? • 10 joules!!! – the potential just turned into the kinetic

  15. Let’s see a demo • 4 different “roller coaster hills” • Which one is going faster at the bottom • Let’s vote and try it out

  16. So from the demo… • All the potential turned into kinetic • The speed at the bottom was the same regardless of how fast it got down there or the hill shape.

  17. Let’s try it out • Find energies of different objects and plot them on bar graphs.

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