Download 14.3 Mechanical Advantage - mrsjanssensclasses

14.3 Mechanical Advantage
and Efficiency
Key Concepts:
1. How does the actual mechanical advantage of a machine compare
to its ideal mechanical advantage?
2. Why is the efficiency of a machine always less than 100%?
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I. Mechanical Advantage
A. Number of times that a machine
increases the input force.
1. Actual mechanical advantage
(AMA) = Output force
Input force
2. Example: Inclined plane
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I. Mechanical Advantage
B. Ideal Mechanical Advantage (AMA)
1. The mechanical advantage in the
absence of friction.
2. Actual mechanical advantage is
always less than the ideal
mechanical advantage.
3. Ideal mechanical advantage =
Input distance
Output distance
https://bvg8science.wikispaces.com/file/view/hammer.jpg/418962594/hammer.jpg
I. Mechanical Advantage
C. Practice Problems
1. A pulley is used to raise a heavy crate. The pulley is such that
an input force of 223 N is needed to provide an output force
of 1784 N. What is the actual mechanical advantage of this
pulley?
http://leos-bridge.org/pulley/gallery/images/compound-pulley.png
I. Mechanical Advantage
2. To pull a weed out of a garden, you can apply a force of 50 N to
the shovel. The shovel applies a force of 600 N to the weed.
What is the actual mechanical advantage of the shovel?
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I. Mechanical Advantage
3. Suppose you need to remove a nail from a board by using a claw
hammer. If the effort length for a claw hammer is 11.0 cm and
the resistance length is 2.0 cm. What is the ideal mechanical
advantage?
http://www.finehomebuilding.com/CMS/uploadedimages/Images/Homebuilding/slideshows/removing-nails_lgsq.jpg
I. Mechanical Advantage
4. A mover uses a ramp to load a crate of nails onto a truck. The
crate, which must be lifted 1.4 m from the street to the bed of
the truck, is pushed along the length of the ramp. If the ramp is
4.6 m long and friction between the ramp and crate can be
ignored, what is the ideal mechanical advantage of the ramp?
http://www.ohio.edu/people/williar4/html/haped/nasa/simpmach/inclp2.gif
II. Efficiency
A. The work output of machine is always less than the work input
due to friction.
B. To measure efficiency of a machine, compare the work output to
work input.
Efficiency = Work output x 100
Work input
II. Efficiency
C. Practice Problems
1. What is the efficiency of a cyclist who expends 900J of work to his
bike for it to produce 76 J of useful work?
II. Efficiency
2. What is the efficiency of a tractor that has a work output of 300J
and a work input of 400 J?
http://www.picgifs.com/graphics/t/tractor/graphics-tractor-044409.gif
II. Efficiency
3. If a steam engine does 500 J of useful work, how much work is
needed to be put in if the efficiency rating of 18%?
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14.4 Simple Machines
Key Concepts:
1. What are the six types of
simple machines?
2. What determine the
mechanical advantage of
the six types of simple
machines?
http://a1.typepad.com/6a015434a267c6970c01b7c731ec29970b-800wi
1. Levers
A. A lever is a rigid bar that is free to move around a fixed point.
B. The fixed point the bar rotates around is the fulcrum.
C. The input arm of a lever is the distance between the input force
and the fulcrum.
D. The output arm is the distance between the output force and the
fulcrum.
http://vhmsscience.weebly.com/uploads/1/2/7/6/12762866/3006320_orig.jpg
1. Levers
E. 1st Class Levers
1. The fulcrum is always
located between the
input force and the output
force.
2. Depending on the fulcrum
position, the mechanical
advantage can be greater
than 1, equal to 1, or less
than 1.
1. Levers
F. 2nd Class Levers
1. The output force is located
between the input force
and the fulcrum.
2. The input distance is larger
than the output distance.
3. The mechanical advantage
is always greater than 1.
1. Levers
G. 3rd Class Levers
1. The input force is located
between the fulcrum and
the output force.
2. The output distance over
which it exerts the force is
larger than the input
distance.
3. The mechanical advantage is
always less than 1.
2. Wheel and Axle
A. Consists of two disks or cylinders,
each one with a different radius.
B. The outer disk is the wheel and the
inner cylinder is the axle.
C. To calculate the IMA, divide the
radius (or diameter) where the
input force is exerted by the
radius (or diameter) where the
output force is exerted.
http://www.buzzle.com/img/articleImages/271899-3617-39.jpg
3. Inclined Plane
A. Slanted surface along which a
force moves an object to a
different elevation.
B. The distance traveled is the
input distance.
C. The change in height of the
ramp is its output distance.
D. The mechanical advantage is
greater than 1.
E. The IMA is the distance along
the inclined plane divided by its
change in height.
https://bvg8science.wikispaces.com/file/view/In%20out%20distance%20ramp%20pic.PNG/419704002/530x227/In%20out%20
distance%20ramp%20pic.PNG
4. Wedge
A. V-shaped object whose sides
are two inclined planes
sloped toward each other.
B A wedge has a mechanical
advantage greater than 1.
http://www.buzzle.com/img/articleImages/604804-1154-11.jpg
5. Screw
A. An inclined plane wrapped
around a cylinder.
B. Screws with threads that are
closer together have a
greater ideal mechanical
advantage.
C. A screw has a mechanical
advantage greater than 1.
6. Pulleys
A. Consists of a rope that fits into
a groove in a wheel.
B. Pulleys produce an output
force that is different in
size, direction, or both,
from that of the input
force.
C. The mechanical advantage of a
pulley can be equal to or
greater than 1.
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6. Pulleys
D. The IMA is equal to the
number of rope sections
supporting the load being
lifted.
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14.4 Assignment
Page 434 #1-9 all
Read Lab: Pulleys