Chapter 10_ Work_ Energy_ and Simple Machines

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					Chapter 10: Work, Energy, and
      Simple Machines
                     Work
• No it’s not your job!
• Work is the product of force and the distance an
  object moves in the direction of force
• Scalar quantity- no direction
• Measured in Joules
• A JOULE is 1 newton of force times one meter of
  movement
• The object must MOVE or there is no work, only
  force
                       Work
• Work only occurs if the force and
  displacement are in the same direction
• Increasing the force or the displacement,
  increases the work done on an object
• FORMULA FOR WORK
     • W = Fd
     • Work = Force times displacement
• Example problem #1
• Practice problems #1-3
  Work and the direction of force
• Force must be exerted in the direction of
  motion for work to be done
• If the force is perpendicular to the motion- NO
  WORK IS DONE!!!
• The object that exerts the force does the work
       Work and angles of force
• What happens when the force is at an angle
  to the motion?
  – Use the amount of force acting on the direction of
    motion
  – Use the formula W = Fd(cos) to determine the
    amount of force in the direction of motion
  – If the work is negative- the object is doing work on
    another object
  – If the work is positive- work is being done on the
    object
       Work and angles of force
• The effect of doing work is the transfer of
  energy from one object to another
• Work is the mechanical transfer of energy
  Steps for solving work problems
1. Carefully check the forces acting on the
   object
       –   You may use vector diagrams to do this
2. Determine the displacement and any angle
   between the force and the direction of
   motion
3. Check the sign (+ or -) by determining the
   direction energy is transferred
       –   If the sign is positive energy has increased
       –   If the sign is negative energy has decreased
                  Practice
• Example problem #2
• Practice problems #5-7
                            Power
• Work does not consider time
• Work to move a stack of 10 objects 1m is the same
  whether you move each object in 2 seconds or 10
  seconds.
• POWER is the rate work is done-
      • more power is required to move the stack of 10 objects in 2
        seconds than is required to move the same stack in 10 seconds
• Power is work done divided by the time it takes to do
  the work
      • P = W/t
      • Measured in watts or kilowatts
      • 1 watt = 1 joule per second
                  Practice
• Example #3
• Practice problems 9-11

• Lab- Page 204
Simple Machines

				
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posted:5/13/2014
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