Transcript Simple Machines

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Sound
Simple Machines
Force
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Goals
What do I
need to know?
Analyze the simple machines qualitatively and quantitatively in
terms of force, distance, work and mechanical advantage
Be able to calculate mechanical advantage
Be able to calculate amount of work done by a simple machine
Explain the different types of simple machines.
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Work
Transfer of Energy from one place to another.
Applying a force over a certain distance.
Calculating Work:
Work= Force x distance
W = f x d
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6 types of simple machines
Wedge
Screw
Simple
Machines
Wheel
and
Axle
Lever
Inclined
Plane
Pulley
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What is a machine?
A device that makes work easier.
You still do the same amt of work —it’s just easier!
What is a simple machine?
-a machine that does work with only one
movement.
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A machine can make work easier in two
ways:
1. Multiply the force you apply.
A Car Jack
2. Change the direction
Blinds
of the force.
7.1
Mechanical Advantage
Number of times the
machine multiplies the
effort force
(The force you apply to it)
IMA
IMA
7.1
Ideal vs Actual Mechanical Advantage
IMA
IMA
WHAT ACTUALLY happened!!
Why is this different from IMA?
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Watch for this in all Simple machines:
Machines are a “give
and take relationship.”
If you get your force
multiplied, then you
must go a greater
distance.
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Types of Machines
A lever is a
bar that is
free to
pivot, or
turn about a
fixed point.
Levers
How can we
use levers?
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Levers
Fulcrum
Resistance
Distance
Effort
Distance
LOAD
Effort Arm
Effort Force
Resistance Arm
Resistance Force
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Levers
There are three types of Levers
Based on the position of the
fulcrum
Levers
1st Class: Crowbars, pliers, scissors, seesaw
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The fulcrum is between the resistance force
and the effort force.
The closer the fulcrum to the resistance
force, the more the lever multiplies the
force.
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Levers
•Wheelbarrow
•Nutcrackers
•Crowbar (forcing two
objects apart)
•The handle of a pair
of nail clippers
2nd Class: The resistance force is
between the effort force and the
fulcrum.
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Levers
3rd Class: the effort force is
between the resistance force and
the fulcrum.
•Garden Hoe
•Your arm
•Catapult
• Fishing rod
•Tongs (double lever) (where hinged at one
end)
Mechanical Advantage of Levers
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3 Ways
5/5=1
Effort arm
Resistance arm
10/5=2
20/5=4
As the length of the effort arm increases, the MA of the lever
increases.
Mechanical Advantage of Levers
You can also use the Mechanical Advantage
Formulas:
IMA
AMA
Ideal MA
Actual MA
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REVIEW
Position of Fulcrum
MA of Levers
Problems
1. To pull apart two pieces of wood, you apply a force of 50
N to a lever. The lever then applies a force of 640 N to the
wood. What is the mechanical advantage of the lever?
2. A lever and fulcrum are used to raise a heavy rock, which
has a weight of 350 N. If the lever has a mechanical
advantage of 9, what must the input force on the lever be
in order to just begin lifting the rock?
3. A construction worker uses a board and log as a lever to
lift a heavy rock. If the input arm is 6 meters long and the
output arm is 1.2 meters long, what is the mechanical
advantage of the lever?
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Efficiency of a Machine
A measure (%) of how
much work
put
into a machine is
actually changed to
useful work put out by
90 J .
100 J
the machine.
NEVER OVER 100%
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Ideal machine
According To “The Law of Conservation
of Energy” Can this exist?
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Pulleys
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• What is a pulley?
Pulleys
– A pulley is a grooved wheel with a rope or chain
running along the groove.
• What can a pulley be used for?
1.Multiply the effort
force
2.change the direction
of the force
Pulleys
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Two types of Pulleys:
1. Fixed pulley
–
–
A pulley that is attached to something
Only changes the direction
of the force
–
The pulley is free to move
2. Movable pulley
***Block and Tackle***
Combination of both types of pulleys
Mechanical Advantage of Pulleys
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10 N
resistance
Force
Effort
Force
10 N
Mechanical Advantage of Pulleys
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Mechanical Advantage of Pulleys
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Mechanical Advantage of Pulleys
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Inclined Plane
A sloping surface that that reduces the amount of force required to
raise and object.
Resistance Distance (h)
Effort Distance (l)
Mechanical Advantage of Inclined Planes
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Resistance Distance (h)
Effort Distance (l)
Mechanical Advantage of Inclined Planes
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31.a
Wheel and Axle
• Consisting of two wheels of different sizes that rotate together
• The effort force is applied to the larger wheel
31.b
Ideal Mechanical Advantage = Radius of wheel
Of wheel and axle
Radius of axle
The effort
force is
applied to
the larger
wheel
Gears are wheels with teeth.
31.c
• One day you made a mousetrap cars.
The car has the following measurements for
their wheels: the radius axle (the small
wheel) measured only 1 cm. The radius of
the larger wheel (the one that touched the
pavement) measured a whopping 10cm. What
was the mechanical advantage of these
wheels?
IMA = 10
Ideal Mechanical Advantage = Radius of wheel
Of wheel and axel
Radius of axel
This means with each turn of the axle,
you get 10 times the distance. Those
big wheels really help!
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Screw
• An inclined plane wrapped around a cylinder
• The inclined plane lets the screw slide into the
wood.
Examples: Bolt, Spiral Staircase
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Wedge
• An inclined plane with one or
two sloping sides.
• Changes the direction of the
Examples: Axe, Zipper, Knife
effort force.
Effort
Force
Resistance force
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Rube Goldburg
Keep You From Forgetting To Mail Your Wife's Letter
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Simplified Pencil Sharpener
CLIP
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A lever is used to lift a box. The
mechanical advantage of the lever is
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A 25
B 10
C5
D4
It took only 200 N of
force to lift a 1000N
50 cm
object, therefore the
machine multiplied
10 cm
the force 5 times!
OR
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What is the amount of useful work output of a 25%
efficient bicycle if the amount of work input is 88 Nm?
A 2200 N-m
B 113 N-m
C 63 N-m
D 22 N-m
.25 =
Wout
88 J
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Which of the following is an example of
a compound machine?
A bicycle
B crowbar
C doorknob
D ramp