WORK

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Chapter 13

• WORK ENERGY

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TN Standards

• CLE 3202.4.3 Demonstrate the relationship among
  work, power, and machines
• CLE 3202.2.6 Investigate the Law of
  Conservation of Energy

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Bellwork

• What is Work?

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Work, Power, and Machines

• Work is conducted only when an applied ( net )
  force results in the change in position of an
  object
• Work is measured in Joules ( J )
• 1 Joule 1 N x 1m
• Work is calculated by multiplying force and
  distance ( over which the force is applied )
• W F x d

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Work, Power, and Machines

• Power is the amount of work conducted over a
  certain time interval
• P W / ?t
• Power is measured in Watts

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Work, Power, and Machines

• Machines help to do work by changing the size of
  an input force, the direction of a force, or both
• Different forces can do the same amount of work
• Figure 3 ( a box lifted vs a box pushed up a ramp
  )

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Simple Machines

• The six types of simple machines are
• Simple lever
• Wheel and axle
• Pulley
• Simple inclined plane
• Wedge
• Screw

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Compound Machines

• A combination of any of those six simple machines
• Example SCISSORS
• Combination of lever and wedge

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Mechanical Advantage / Efficiency

•  

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Bellwork

• What is Energy?

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What is Energy?

• Energy is a property of an object due to its
  motion or its position
• When work is done, energy is transferred or
  transformed from one system to another
• Carry a tennis ball up in the stadium
• You add potential energy to it by carrying it up

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What is Energy?

• Energy is measured also in Joules ( J )
• Potential energy energy of position
• PE hmg
• h is height g is gravity m is mass
• Height is relative
• Kinetic Energy energy of motion
• KE ( ½ ) mv2
• m is mass v is velocity

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Other Forms of Energy

• Mechanical energy
• Non-mechanical energy
• ( atomic level )
• Chemical reactions involves chemical energy ( a
  form of potential energy )
• Sun gets energy from nuclear reactions
• Electrical energy ( stored in electric fields )

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Conservation of Energy

• Energy easily changes from one form to another (
  battery )
• PE can become KE ( tennis ball dropped from the
  top of stadium )
• Vice-versa ( projectile shot / reaches max height
  )
• Law of Conservation of Energy?
• ( neither created nor destroyed )

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Roller Coaster Example
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Thermodynamics

• For any system, the net change in energy equals
  the energy transferred as work and heat
• Efficiency ( how much energy/work you get out of
  a machine or process compared to how much is put
  in )
• Internal Combustion Engine