Energy,%20Work,%20and%20Transfer%20of%20Energy

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Energy, Work, and Transfer of Energy

• Physical Science Chapter 12

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Potential Energy

• The stored energy an object has because of the
  position or condition.
• The energy that has not been released yet
• EX stretching a rubber band (elastic PE)
• EX an apple on a tree (gravitational PE)

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Calculating PE

• PE (mass)(gravity)(height)
• Gravity 9.8m/s2
• Calculate the PE of a 20 kg object that is
  sitting on a shelf 5 meters above the ground.
• PE (20)(9.8)(5)
• PE 980 Joules

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Kinetic Energy

• The energy of a moving object
• KE depends on mass and speed
• Ex A small increase in speed produces a large
  increase in KE
• EX once the apple falls from the tree it is
  doing work or releasing energy

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Calculating KE

• KE .5(mass)(velocity2)
• What is the KE of a 44kg cheetah running at 31
  m/s?
• KE .5(44)(312)
• KE 21,000 Joules

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Transfer of Energy
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Transfer of Energy
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Conservation of Energy

• Energy cannot be created or destroyed
• Energy will change forms but never disappears
• Energy can be exchanged out of the system as
  friction, heat (thermal energy), or sound.

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Work

• The transfer of energy caused by a force that
  makes the object move.
• In order for work to be done, there must be
  motion of the object.
• EX If you try to lift the front of a caryou
  will apply a large force, but if the car does not
  move you have not done work on the car.

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Work Equation

• Work Force Distance
• Measured in Joules
• Example A father lifts his daughter repeatedly
  into the air. How much work does he do with each
  lift, assuming he lifts her 2.0 meters and exerts
  an average force of 190 N?
• F 190 N d 2.0m
• W Fd
• W 190 N 2.0 m 380 Joules

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Energy and Work

• Whenever work is done, energy is transferred to
  another system
• Energy is the ability to do work
• Unit for Energy - Joule

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Practical Examples of Energy Transfers
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