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Potential and Kinetic Energy Energy: is the ability to do work

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Kinetic Energy = the energy an object possesses because of its motion The amount of Kinetic energy is dependent on the mass of the object in motion and it’s velocity.

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VELOCITY Velocity = distance ÷ time Distance = meters Time = seconds

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Calculating kinetic energy If we know the mass of an object and its velocity we can determine the amount of kinetic energy possessed by using the following formula: kinetic energy = 1/2 (mass of object)(velocity of object) 2 or KE = 1/2 mv 2 or KE = 0.5mv 2 The SI unit for kinetic energy is the Joule (J). A Joule is kg m 2 /s 2

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A bicycle with a mass of 14 kg traveling at a velocity of 3.0 m/s east has how much kinetic energy? KE = 0.5mv 2 = 0.5(14 kg)(3.0 m/s) 2 = 0.5(14 kg)(9.0 m 2 /s 2 ) =63 kg x m 2 /s 2 = 63 J

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A 1200 kg automobile is traveling at a velocity of 100 m/s northwest. What is the kinetic energy of the automobile? KE = 0.5 mv 2 = 0.5(1200kg)(100 m/s) 2 = 0.5(1200 kg)(10 4 m 2 /s 2 ) = 6 x 10 6 kg m 2 /s 2 = 6 x 10 6 J

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Potential Energy The energy of position The amount of energy contained in an object at rest

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Determining Potential Energy By its position and its weight (mass X gravity) PE = (mass)(gravity)(height) = mgh where m is mass in kg g is the force of gravity = 9.8 m/s 2 h is the height The SI unit that represents potential energy is the Joule (J) (kg m 2 /s 2 ).

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Examine an example of potential energy A flower pot with a mass of 15 kg is sitting on a window sill 15 meters above the ground. How much potential energy does the flower pot contain? PE = (mass)(gravity)(height) = (15 kg)(9.8 m/s 2 )(15 m) = 2205 kg m 2 /s 2 = 2205 J = 2.2 x 10 3 J

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Examine an example of potential energy If the flower pot is lowered to a window sill that is 10. m from the ground. Does this change the potential energy of the flower pot? PE = (mass)(gravity)(height) = (15 kg)(9.8 m/s 2 )(10. m) = 1470 kg m 2 / = 1470 J = 1.5 x 10 3 J

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Potential or Kinetic Energy? Moving car Tree branch Bent car fender Balloon filled with air Balloon squirting around room Person inside a moving car

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What type of energy does the space shuttle have at lift off?

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Conversion of Potential to Kinetic Energy In this picture both kinds of energy are evident. Can you point them out?

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The water at the top has potential energy When water falls to a lower level, the potential energy is converted to kinetic energy.

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Example

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