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

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

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.

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

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

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

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

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

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 ).

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

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

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

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

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

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

Example

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