Energy and Work

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Energy and Work
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Big Idea

• Energy and matter are conserved.

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What do you think?

• What do we mean when we say something has
  energy?
  
• What types of energy are there?

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Essential Questions

• What are energy and work and how are they
  related?
  
• What is mechanical energy?
• Under what circumstances is mechanical energy
  conserved?

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Energy

• The ability to cause change or do work.
• The stuff that makes things move

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Kinds of Energy

• Chemical
• Elastic
• Gravitational
• Nuclear

• Electromagnetic
• Thermal
• Kinetic

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Mechanical Energy

• Gravitational Potential Energy
• Stored energy

• Kinetic Energy
• Energy of motion

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Work

• Transfer of energy through motion
• Only force in the direction of motion does work.

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Power

• Rate of work done or energy expended
• Work or Energy per time

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Conservation of Energy

• The total amount of energy in the universe is a
  constant.
  
• Energy cannot be created or destroyed, only
  transferred or transformed.

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• Bud, a very large man of mass 130 kg, stands on a
  pogo stick. How much work is done as Bud
  compresses the spring of the pogo stick 0.05 m?

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• After finishing her homework, Susan pulls her 50
  kg body out of the living room chair and climbs
  up the 5.0 m high flight of stairs to her
  bedroom. How much work does Susan do in
  ascending the stairs?

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• In the previous example, Susan slowly ascends the
  stairs, taking 10 s to go from bottom to top.
  The next evening, in a rush to catch her favorite
  TV show, she runs up the stairs in 3.0 s. a) On
  which night does she do more work? B) On which
  night does she generate more power?

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• In a wild shot, Bo flings a pool ball of mass
  0.10 kg off a 0.68 m high pool table and the
  balls hits the floor with a speed of 6.0 m/s.
  How fast was the ball moving when it left the
  table? (Use the law of conservation of energy.)