Chapter 12 Work and Machines

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					Chapter 12 Work and
     Machines
    Section 1 - What is work?
Work - The product of force and distance
 when a force is used to move an object.
  No work without motion

Work = Force x Distance
  work units - Joules (J)

Problems pg 376
                     Chapter 12
     Section 2 - Mechanical
    Advantage and Efficiency
Machine -
   A device that changes the amount of force exerted or
    the direction in which force is exerted.
   A device with which you can do work in a way that
    is easier or more effective.
A machine makes work easier by changing the
 amount of force you exert, the distance over
 which you exert your force, or the direction in
 which you exert your force.
                         Chapter 12
Overhead - input/output force pg.379
Increase force, decrease distance
Increase distance, decrease force
Mechanical advantage (MA) = output
 force/input force
Friction reduces mechanical advantage
Efficiency = output work/input work x 100%


                     Chapter 12
  Section 3 - Simple Machines
Six types of machines
  Inclined plane
  Wedge
  Screw
  Lever
  Wheel & axle
  Pulley

                    Chapter 12
             Inclined Plane
Less force exerted over longer distance




                      Chapter 12
                  Wedge
Less force exerted over longer distance




                      Chapter 12
                  Screw
Inclined plane wrapped around a cylinder
  Less force




                     Chapter 12
                   Lever
 Fulcum - the fixed point that a lever pivots around




                           Chapter 12
3 Types of Levers




          Chapter 12
          Wheel and Axle
Less force
 exerted
 over longer
 distance
  Doorknob




               Chapter 12
                 Pulley
Change amount and direction of input force




                       Chapter 12
   Section 4 - Machines in the
          human body
Lifting levers - most of the machines in
 your body are levers that consist of bones
 and muscles.
Overhead -pg.401 Levers in the body
Wedges - front teeth (incisors)
Break toothpick in fingers


                    Chapter 12
         Ch. 12 Vocabulary
work,                  wedge,
machine,               screw,
efficiency,            lever,
mechanical             fulcrum,
 advantage,             wheel and axle,
inclined plane,        pulley



                   Chapter 12

				
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posted:11/26/2011
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