unit 6 – lecture 1. review work = force * distance measured in joules [newton meters] this remains...
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Unit 6 – Lecture 1
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ReviewWork = Force * distance
measured in Joules [newton meters]this remains true using effort force
or resistance force
Power = Work / timemeasured in Joules per second
Mechanical Advantage = Force(out) / Force(in)
Efficiency = Work(out) / Work(in) * 100
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MachinesA Simple Machine accomplishes the work in
one motion.
A Compound Machine is made up of two or more simple machines. Most machines are compound machines.
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Simple MachinesThere are six types of simple machines:
LeverWheel-and-AxlePulleyInclined PlaneWedgeScrew
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Helpful NoteALL of the equations for the mechanical
advantage of different types of machines will be given to you for the test [which will take place tentatively on Monday, 2/8].
Ideal vs. Actual Mechanical EfficiencyIdeal = according to the equationActual = taking into account the efficiencyex: MA = 2 but machine only has a 94%
efficiency2 = the ideal MA2* .94 = actual efficiency. MA = 1.88
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LeverA Lever is comprised of:
a bar (straight or curved)a fixed point called the
fulcrum on which the bar pivots
Bar
Fulcrum
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LeverThe distance from where the effort force is
applied to the fulcrum is the Effort Arm of the lever.this is where your effort is done
Effort Arm
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LeverThe distance from the fulcrum to where the
resistance force is applied is the Resistance Arm.
Resistance Arm
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LeverThere are three classes of levers:
class is determined by where the location of the effort force, resistance force (load), and the fulcrum
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Lever1st class lever:
see-Saw (Teeter-Totter)prying up a lid by
pushing down on a barpairs: scissors, pliers,
hedgeclippers
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Lever2nd class lever:
doorwheelbarrow armspairs: shears,
nutcracker
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Lever3rd class lever:
NOTE: MA = < 1 effort increases to increase distance of
loadtweezers!anything you swing
bat, sword, stick, golf clubbrooms, rakes, mops
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MALeverThe MA of a lever is calculated as:
MALever = Effort Arm Resistance Arm
(again, both in units of length, so there are no
MA units)
The longer the effort arm, the more the MA[the better it is for you]recall: increase distance, less force
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PracticeWhat is the MA of a lever with an Effort Arm
of 6 m and a Resistance Arm of .3 m?
Which type of lever does not increase the force output of the machine?
If a lever has a MA of 9, and a force of 6 N is applied, how much force will the lever apply?
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Wheel-and-AxleWheel & Axle - a simple machine made of two
circles of different diameters that rotate together.The outer circle (wheel) is turned with less
force over a larger distance so that the inner circle (axle) turns with more force over a shorter distance.
Ex. Steering wheels, door knobs, faucet handles
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MAWheel&Axle
MA = radiusWheel
radiusAxle
Explains how to steer larger vehicles with less force
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PracticeWhat is the MA of a Wheel with a 50 cm
radius connected to an Axle with a 2.5 cm radius?
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PulleyPulley - a simple machine comprised of a
wheel with a rope or chain running around it.The MA of a pulley system is equal to the
number of ropes which support the object, because the weight is distributed.
MA = 1no
difference
MA = 2no
difference
MA = 3no
difference
MA = 4no
difference
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PulleyThere are two types of pulleys
Fixeddo not move,
merely redirect force
Moveableattached to the object
being pulled and multiply forcerises and falls with the object
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PulleyBlock and Tackle System - a multiple-pulley
system where large amounts of distance are converted into force.composed of a fixed pulley & a moveable
pulleyMA = number of supporting ropes
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PracticeWhat is the MA of this pulley system?
2
What is the effort force?[give in pounds of force]35 lbs
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PracticeWhat is the MA of this pulley system?
3
What is the effort force?[give in pounds of force]23.3 lbs
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PracticeWhat is the Force Output of this pulley
system?50 N