# 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?
 Calculating the “ease” of a machine is
 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?_____________