Mechanical Advantage _ Efficiency by qingyunliuliu

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									Mechanical Advantage &
      Efficiency
      WORK, WORK, WORK!
 A “Work” Fundamental: A person CANNOT
  get out of doing work…one can only
  sacrifice force for distance or vice versa
     (Reminder: Work = Force x Distance)
 Work input = Work output = Kinetic Energy
  F x D (input) = F x D (output) = ½ mv2
         F=5
         D=2
                    F = 10      KE = 10 J
                    D=1
              Simple Machines
   Work can be re-distributed by simple machines,
    of which there are 6:




                                       WHEEL & AXLE
          Compound Machines
 Any combination of simple machines is
  called a compound machine.
 Example: Can opener
    – Wedge (teeth)
    – Wheel & axle (crank)
    – Lever (handle)
How many machines can you count?
         Mechanical Advantage
 Calculating the “ease” of a machine is
  called the Mechanical Advantage (MA).
 The higher the mechanical advantage
  number, the less force is needed.
    – Example: an MA of 2 means that it is 2x
      easier to do, or ½ the force is needed.
                                  IMA
   Ideal Mechanical Advantage (IMA): The theoretical
    MA if NO friction was involved.

IMA for a pulley is the #           IMA for a lever is calculated by…
of strings DIRECTLY
supporting the object…              Effort Distance           2
                                                          =
                                    Resistance Distance       1



                        IMA = 2                       ED=2
                                        RD=1
                                 AMA
   Actual Mechanical Advantage (AMA) is the REAL
    advantage, and is less than IMA because of
    friction.


      AMA = Resistance Force (RF)   =   force by machine
             Effort Force (EF)          force by you


AMA is always less than IMA…why? FRICTION is
the culprit!
                 Efficiency
 Efficiency: The percentage of work input
  that gets directly transferred to work
  output. (the rest is lost mainly to friction)
 100% efficiency only occurs theoretically
  or “ideally” (hence IMA)
                          Efficiency
   Calculate efficiency 3 different ways:
    1) (Actual) AMA x 100 = _____ %
       (Ideal) IMA
    2) Work (Output) x 100 = ______%
       Work (Input)
    3)   Resistance Force x Resistance Distance   x 100 = ___%
              Effort Force x Effort Distance
          RF x RD
          EF X ED
                         Assignment
1. RF = 6000 N          EF= 4000N                MA=________________

2. RD = 40 m            ED= 1200 m               MA=________________

3. Using a lever to move a boulder, Ben applies 256 newtons of force and
    moves the lever 12.0 meters. The weight of the boulder is 540 newtons.
    If the boulder is moved 0.20 meters, what is the percent efficiency of
    the lever?

4. It took 150 N of force for Andy to lift a box weighing 2350 N with a
    pulley.
What is the mechanical advantage of the pulley?_____________
Was this an ideal or actual mechanical advantage? ______________

5. John wants to lift a box weighing 82 N up on to a shelf that is 1.2 m
    high . If he does this task in 16 seconds, how much power will be
    needed?

								
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