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Unit 6 – Lecture 1
EquationsWork = 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) (or… Force (resistance) / Force (effort))
Efficiency = Work(out) / Work(in) * 100
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.
Simple MachinesThere are six types of simple machines:
LeverWheel-and-AxlePulleyInclined PlaneWedgeScrew
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
LeverA Lever is comprised of:
a bar (straight or curved)a fixed point called the
fulcrum on which the bar pivots
Bar
Fulcrum
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
LeverThe distance from the fulcrum to where the
resistance force is applied is the Resistance Arm.
Resistance Arm
LeverThere are three classes of levers:
class is determined by location of the Fulcrum, Resistance Force, and Effort Force
(F) (R) (E)
1st Class Lever1st class lever:
fulcrum in middle
see-Saw (Teeter-Totter)pairs: scissors, pliers,
hedgeclippers
1st Class Lever
Lever2nd class lever:
load / resistance in middle
doorwheelbarrow armspairs: shears,
nutcracker
2nd Class Lever
Lever
3rd Class Lever
ReviewWhat was the equation relating FORCE to
MA?
MALeverThe MA of a lever is calculated as:
MALever = Effort Arm Length Resistance Arm Length
(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
PracticeWhat is the MA of a lever with an Effort Arm
of 6 m and a Resistance Arm of .3 m?20
Which type of lever does not increase the force output of the machine?third class
If a lever has a MA of 9, and a force of 6 N is applied, how much force will the lever apply?MA = Force of Resistance / Force of Effort 9 = FR / 6 = 54 N
PracticeWhat type of lever is each of the following?
PracticeWhat type of lever is each of the following?
claw hammer [prying a nail out]nut crackerhuman armplierstongs / tweezerswheel barrow
Answers
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
MAWheel&Axle
MA = radiusWheel
radiusAxle
Explains how to steer larger vehicles with less force
PracticeWhat is the MA of a Wheel with a 50 cm
radius connected to an Axle with a 2.5 cm radius?MA = radius(wheel) / radius(axle)= 50 / 2.5 = 20
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 = 1 MA = 2 MA = 3 MA = 4
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
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
PracticeWhat is the MA of this pulley system?
2
What is the effort force?[give in pounds of force]35 lbs
PracticeWhat is the MA of this pulley system?
3
What is the effort force?[give in pounds of force]23.3 lbs
PracticeWhat is the Force Output of this pulley
system?50 N
HomeworkComplete
Types of Levers w/s on page 4
If finishing early…1) begin page 5 Simple Machines Matching2) review vocabulary [due tomorrow – ch 5]