Transcript Simple Machines

Simple Machines
5.2
SIMPLE MACHINES: ease load, changing
either magnitude or direction of a force
WORK input<WORK output
FORCE exerted<FORCE machine
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LEVER
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Simple Lever
Pulley
Wheel and axle
INCLINED PLANE
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Simple Inclined Plane
Wedge
Screw
The Lever Family!
EXAMPLES
 Claw hammer
 Crowbar
 See-saw
A bar that is free to pivot or turn at a
fixed point.
-Fixed point=Fulcrum
-Input Arm=Distance from the fulcrum to where the
input force is.
-Output Arm=distance from the fulcrum to the output
force.
Three classes
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1st class lever: Claw hammer, the fulcrum
is located in the middle of the arm.
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2nd class lever: The fulcrum is located at
the end of the arm, output force is b/t
input force and fulcrum: A wheelbarrow.
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3rd class lever: The fulcrum is located at
an end of the arm, the input force is
applied b/t the output force and fulcrum.
Pulleys
Pulleys are modified levers.
 Fixed Pulley-change direction of the input
force
 Movable Pulley- increase input force.
 Axel = Fulcrum
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Depending on the number and
arrangement of pulleys, the mechanical
advantage is different.
 Fr=Fe Mechanical Advantage =1 w/ 1
fixed pulley
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Block and Tackle-System w/ fixed and
movable.
Wheel and Axle
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Axle in the center of the wheel
Inclined planes
Inclined planes
- multiply and redirect forces.
 Wedge
- is a modified inclined plane
 Screw
- is an inclined plane wrapped around a
cylinder.
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Compound Machines
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Two or more simple machines
Using Machines
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Increase Force
Change Direction
Make Work Easy
INPUT FORCE-Force applied to the machine
 OUTPUT FORCE-Applied by the machine
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Mechanical Advantage= Ratio Output Force/Input
Force

Fresistance/Feffort
Ideal Mechanical Advantage (IMA)=equal to the
displacement of the effort force divided by the
displacement of the load.
Fr/Fe=de/dr
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Efficiency (%) = Output Work/Input Work x
100%
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MA/IMA x100
Practice Problem:
1.) You examine the rear wheel on your bicycle. It has a radius of
35.6 cm and has a gear with a radius of 4 cm. When the chain is
pulled with a force of 155 N, the wheel rim moves 14 cm. The
efficiency of this part of the bicycle is 95%.
 A. What is the IMA of the wheel and gear: 4 cm/35.6 cm=0.112
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B. What is the MA of the wheel and gear: e=ma/IMAx 100
MA=e/100 xIMA
(95/100) 0.112= 0.106
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C. What is the resistance force: MA=Fr/fe Fr=Max Fe
0.106(155)=16.4
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D. How far was the chain pulled to move the rim 14 cm:
IMA=de/dr
de=IMA x dr
0.112(14)=1.57 cm
2. A sledgehammer is use dto drive a wedge into a log to split
it. When the wedge is driven 0.2 m into the log, the log is
separated a distance of 5 cm. A force of 17000 N is
needed to split the log and the sledgehammer exerts a
force of 11000.
a.
What is the IMA of the wedge?
(4)
a.
What is the MA of the wedge?
(1.5)
a.
Efficiency?
(38%)
Impulse
Average force times time
 F=ma….
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Ns
Momentum
Mass times velocity
 Kg m/s
 Vector
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Impulse Momentum Theorem
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Impulse is the change in p
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CONSERVATION OF MOMENTUM:
pi=pf
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