Simple Machines
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There are 6 basic simple machines.
Simple machine do not decrease the amount of work we must
do, they make the work easier by decreasing the amount of force
we must apply.
WInput = WOutput
• Hence, Finput dinput = Foutput doutput
• Notice that cos(θ) has been omitted since the direction of
motion and force is 0.
• Also, notice that all of these may have different names
such as effort, load or resistance.
d
F
Fd 
• Remember in all these cases the Winput = Woutput
• Thus the man above applies a small force (FI) over a
big distance (dI) while the rock moves upward with
big force (FO) over a small distance (dO).
Mechanical Advantage
• Is the amount a machine amplifies an applied force.
• Hence, a you would only need to apply 50 N of force to
a machine with MA = 2 in order to lift 100 N.
• Ideal mechanical advantage (IMA) is the advantage
gained by a 100 % efficient machine (i.e. no friction).
• MA can always be determined by dividing the Foutput by
the Finput (however, certain simple machines have other
ways of determining this value).
Levers
• 3 types:
– Class 1 – Fulcrum is between
the effort and the load
(scissors, crowbar).
– Class 2 – Load is between the
fulcrum and the effort
(wheelbarrow, bottle opener).
– Class 3 – Effort is between
the fulcrum and the load
(tweezers, your arm).
• Another way of determining the MA of a lever is
to divide the effort length by the resistance length.
Problem 1:
(a) A lever used to lift a heavy box has an input arm of 4 meters and an output arm
of 0.8 meters. What is the mechanical advantage of the lever?
(b) If you pushed down with 20 N of force over a distance of 0.80 m how much
work did you accomplish?
(c) How high was the box raised?
(d) What is the mass of the box?
Problem 2:
A broom with an input arm length of 0.4 meters has a mechanical advantage of 0.5.
What is the length of the output arm?
Pulley
• Is really just a glorified lever!
• MA is determined by counting the number of supporting
strands (subtract one if the strand just changes the direction of
the applied force).
• Be careful with change of force direction strand!
• In each of these pulley systems find:
• the MA
• the effort force
• the amount of rope that must be pulled to raise the load 0.50 m
Inclined Plane/Ramp
• The output work of the load is the vertical distance traveled or mgh.
• The MA can be determined by dividing the length of the ramp by its
vertical height.
Practice Problems
• A 5 meter ramp lifts objects to a height of 0.75 meters. What is the
mechanical advantage of the ramp?
– How much work would be required to bring a 10 kg object to the
top of this ramp?
– What would be the input force required to use this ramp?
• Gina wheels her wheelchair up a ramp using a force of 80 N. If the
ramp has a mechanical advantage of 7, what is the output force?
• A mover uses a ramp to pull a 1000 N cart up to the floor of his truck
(0.8 m high). If it takes a force of 200 N to pull the cart, what is the
length of the ramp?
Image Sources
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http://capocci.pbworks.com/w/page/22877939/Simple%20Machines
http://www.science-class.net/Notes/Notes_simple_machines_7th.htm
http://campus.murraystate.edu/academic/faculty/tderting/atlases2009/runyon/Whatle
ver.html
http://etc.usf.edu/clipart/35900/35944/lever_35944.htm
http://www.pbs.org/wgbh/nova/teachers/activities/27po_sle2phar.html
http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/lever.html
http://en.wikipedia.org/wiki/Mechanical_advantage_device
http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/lever.html
http://www.schoolphysics.co.uk/age1114/Mechanics/Forces%20in%20motion/text/Pulleys_/index.html
http://www.phy.ilstu.edu/pte/489.01content/simple_machines/simple_machines.html
http://road-to-psle.blogspot.com/2008/10/simple-machines-incline-plane.html