Energy

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Energy

• Chapter 4

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The nature of energy

• Energy The ability to do work or cause change
• All energy involves either motion or position
• Where are we using energy right now?

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What are some types of energy?

• Thermal energy The total kinetic energy of
  particles that make up an object
• Chemical energy The energy of a compound changes
  as the atoms are rearranged to form new compounds.

• Electrical energy the energy of moving electrons
• Sound energy The energy of vibration
• Light energy The energy of vibration of
  electrically charged particles
• Nuclear energy the energy associated with
  changes in the nucleus of an atom

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Mechanical NRG

• Mechanical energy is the total amount of
  potential and kinetic energy in a system

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Kinetic energy

• Kinetic energy is energy in the form of motion.

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Potential energy is stored energy because of
position or shape
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Energy transfer
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How to calculate kinetic energy

• Kinetic energy ½ (mass x velocity 2) or
• KE ½ (mv2)
• Labeled as Joules
• Joule is expressed in N x m or
• 1 Joule 1 kg (m/s)2

• What is the kinetic energy of a 45 kg object
  moving at 13 m/sec?
• mass 45 kg velocity 13 m/sec
• KE ½ (mv2)
• So KE 1/2 (45 kg)(13 m/sec)2
• Solving the equation gives a kinetic energy value
  of 3802.5 J

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Calculate

• Determine the kinetic energy of a 1000-kg roller
  coaster car that is moving with a speed of 20.0
  m/s.
• KE (0.5) (1000 kg) (20 m/s)2
• KE 200 000 Joules

• If the roller coaster car in the above problem
  were moving with twice the speed, then what would
  be its new kinetic energy?
• KE 0.51000 kg(40 m/s)2
• KE 800 000 Joules
• As your speed doubles your kinetic energy
  quadruples.

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Gravitational Potential Energy

• Grav. Potential energy weight x height
• Or..
• PE w x h
• Elastic Potential energy energy stored by
  compressing or stretching something

• A 37 N object is lifted to a height of 3 meters. 
  What is the potential energy of this object?
• weight 37 N height 3 meters
• Solving the problem gives a potential energy
  value of 111 J.

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