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Energy

Energy. What is it?. What is it?. Here are some examples:. Definition. Energy is the ability to cause change Two types of energy Kinetic Potential. Kinetic. Energy in the form of motion Running Throwing Flying How much kinetic energy depends on what? Mass and Velocity

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Energy

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  1. Energy What is it?

  2. What is it? • Here are some examples:

  3. Definition • Energy is the ability to cause change • Two types of energy • Kinetic • Potential

  4. Kinetic • Energy in the form of motion • Running • Throwing • Flying • How much kinetic energy depends on what? • Mass and Velocity • Question: What has more kinetic energy: a truck traveling at 100 km/hr or a motorcycle traveling at 100 km/hr • How about a truck traveling at 100 km/hr or a truck traveling at 80 km/hr

  5. Potential Energy • Stored Energy • Students sitting in their seats • A bullet in a gun • Battery • Potential energy changes into kinetic energy

  6. Work • Transfer of energy through motion • In order for work to take place, a force must be exerted through distance • Calculating Work: • Work = Force x Distance or W = F x D

  7. Units • Work is expressed in Newton-meters (N x m) Or Joules (j) Named after British Scientist James Prescott Joule

  8. Example • A student’s full backpack weighs 30 N. She lifts it from the floor to a shelf 1.5 m high. How much work is done on the pack full of books? • W = F x D • F= 30 N • D = 1.5 m • W = ? • W= 30N x 1.5 m • W = 45 N x m or 45 J

  9. Try This One • A carpenter lifts a 4.5 kg beam 1.2 meters. How much work is done on the beam? • What do you know? • Distance = 1.2 m • Force = ? You must calculate force • F = M x A M = 4.5 kg A = ? • A = gravity = 9.8 m/s2 • F = 4.5 kg x 9.8 m/s2 F = 44.1 N • W = 44.1N x 1.2 m W = 52.92 J

  10. Another Example • A man pushes a lawnmower with a force of 500 N for 200 m. How much work is this if the force of friction acting on the lawnmower is 150 N? • W = F x D • F = 500 N + 150 N • D = 200 m • W = 650 N X 200 m • W = 130000 Joules

  11. One more example • Cheerleader A is holding up cheerleader B. Cheerleader B is exerting a force a 80 N on cheerleader A. If cheerleader A walks forward 2 meters while holding cheerleader B, how much work has cheerleader A done? • No work!!!! Why? • Because work was not done over a distance • W = F x D • W = 80 N x 0 m • W = 0 N x m or 0 Joules

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