Chapter 5 Work & Machines

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					    Chapter 5 Work & Machines
I. Work
   A. What is work?
      1. Work is the transfer of energy that occurs when a force
         makes an object move.
      2. There are two conditions that have to be satisfied for
         work to be done on an object:
        a. the applied force must make the object move
        b. the movement mist be in the same direction as the
           applied force
 B. Work and Energy
    1. When work is done, a transfer of energy always occurs.
    2. Energy is the ability to cause change or to do work.
    3. Energy is always transferred from the object that is
       doing the work to the object on which the work is done.
    4. The amount of work done depends on the amount of
       force exerted and the distance over which the force is
       applied.
Work Equation: W=Fd
          work (joules)= applied force (Newtons) X distance (meters)
C. Power
  1. Power is the amount of work done in one second/the
     rate at which work is done or energy transferred.
  2. When work is done, power can be calculated from the
     equation: Power=work/time
     P (in watts)=W (in joules)/t (in seconds)
  3. When energy is transferred, power can be calculated
     from the equation: Power=energy transferred/time
     P (in watts)=E (in joules)/t (in seconds)
II. Using Machine
   A. What is a machine?
      1. A machine is a device that makes doing work easier.
      2. Machines can make work easier by
        a. increasing the force that can be applied to an object
        b. increasing the distance over which a force can be
           applied
        c. changing the direction of an applied force
   B. The Work Done by Machine
      1. Two forces are involved when a machine is used to do
         work.
        a. you exert a force on the machine (input force)
        b. the machine exerts a force on the object (output force)
2. Two kinds of work need to be considered when you use
   a machine:
  a. the work done by you on the machine (input work)
  b. the work done by the machine (output work)
3. Because energy is always conserved, Wout is never
   greater than Win.
4. The machine does not transfer all of the energy it
   receives to the object, some of the energy changes to
   heat due to friction therefore Wout is always smaller than
   Win
5. For an ideal machine, input work=output work
C. Mechanical Advantage
  1. Mechanical advantage is the ratio of the output force to
     the input force
  2. Mechanical Advantage Equation:
     MA= Fout/Fin
  3. The mechanical advantage of a machine without friction
     is called the ideal mechanical advantage, or IMA.
  4. IMA is calculated by dividing the input distance by the
     output distance
D. Efficiency
  1. Efficiency is a measure of how much of the work input into a
     machine is changed into useful output work by the machine
  2. A machine with high efficiency produces less heat from friction so
    more of the input work is changed to useful output work,
3. Calculating Efficiency
   efficiency= Wout/Win x 100
4. Efficiency of an ideal machine would be 100%,
   whereas the efficiency of a real machine would be less
   than 100% because friction causes the output work to
   always be less than the input work.
5. Machines can be made more efficient by reducing
   friction. This is done by adding a lubricant.
6. A lubricant (oil or grease) fills in the gaps between the
  surfaces enabling the surfaces to slide past each other
  more easily.
III. Simple Machines
     1. A simple machine is a machine that doe work with only one
         movement of the machine.
  A. Types of Simple Machine (6 types)
       a. lever-a bar that is free to pivot or turn around a fixed point
       b. pulley-is a grooved wheel with a rope, chain, or cable running along the
          groove
       c. wheel & axle-is a simple machine consisting of a shaft or axle attached to
           the center of a large wheel, so that the wheel and axle rotate together
       d. inclined plane- sloping surface such as a ramp that reduces the amount of
           force required to do work
       e. screw-an inclined plane wrapped in a spiral around a cylindrical post
       f. wedge-an inclined plane with one or two sloping sides
A. Levers
   1. The fixed point the lever pivots on is called the fulcrum.
   2. There are (3) classes of levers. The difference among
      the (3) classes of levers depend on the locations of the
      fulcrum, the input force, and the output force
3. First-Class Lever The fulcrum is between the input force and the
   output force
4. Second-Class Lever The output force is between the fulcrum and
   the input force; output force is always greater than the input force
5. Third-Class Lever The input force is between the fulcrum and the
   output force; the output force is always less than the input force
   6. The ideal mechanical advantage , or IMA, can be
      calculated for any machine by dividing the input
      distance by the output distance. IMA=Lin (m) / Lout (m)
B. Pulleys
   1. Different types of pulleys
    a. A fixed pulley is attached to something that does not
       move, such as a ceiling or wall
    b. A movable pulley is a pulley in which one end of the
       rope is fixed and the wheel is free to move
    c. The block and tackle a system of pulleys consisting of
       fixed and movable pulleys
C. Wheel & Axle
  1. In wheel and axle, the input force is applied to the
     wheel and the output force is exerted by the axle
  2. Calculating ideal mechanical advantage of Wheel and
     Axle: IMA=rw (radius of wheel)/ra (radius of axle)
  3. IMA can be increased by increasing the radius of the
     wheel.
  4. Gears are a type of wheel and axle with the wheel
     having teeth around the rim; When the teeth of two
     gears interlock, turning one gear causes the other
     gear to turn.
   5. If the input force is applied to the larger gear, and it
      rotates clockwise, the smaller gear rotates
      counterclockwise.
D. Inclined Planes
   1. Calculating mechanical advantage of an inclined plane
      IMA= length of slope (m)/height of slope (m)
   2. The IMA of an inclined plane for a given height is
       increased by making the plane longer.
E. The Screw
   1. Input force is applied by turning the screw; IMA of a
      screw is related to the spacing of the threads
    4. IMA of a screw is larger if the threads are closer
       together; if the IMA is larger, more turns are needed to
       drive it into some material
E. The Wedge
   1. A wedge is also a simple machine where the inclined
      plane moves thru an object or material
F. Compound Machines
   1. Two or more simple machines that operate together

				
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