Simple Machines
Work or Not?
• What is work
and what is not?
• a teacher
lecturing to her
class
• a mouse pushing
a piece of
cheese with its
nose across the
floor
What is work?
• In science, the word work has a
different meaning than you may be
familiar with.
• The scientific definition of work is:
using a force to move an object a
distance (when both the force and the
motion of the object are in the same direction.)
Work or Not?
• Now, according to
the scientific
definition, what is
work and what is
not?
• a teacher lecturing to
her class
• a mouse pushing a
piece of cheese with
its nose across the
floor
What’s work?
• A scientist delivers a speech to an
audience of his peers.
• A body builder lifts 350 pounds above
his head.
• A mother carries her baby from room
to room.
• A father pushes a baby in a carriage.
• A woman carries a 20 kg grocery bag
to her car?
What’s work?
• A scientist delivers a speech to an
audience of his peers. No
• A body builder lifts 350 pounds above
his head. Yes
• A mother carries her baby from room
to room. No
• A father pushes a baby in a carriage. Yes
• A woman carries a 20 km grocery bag
to her car? No
• Your family is moving! You can’t leave your house
without your favorite rock from your rock garden!
(how would you make any friends without it to show off)
•
You have a slight problem… how can you get the
rock into the back of the truck without hurting
yourself?
Your Favorite Rock
(actual size)
You
Truck
• You could create a ramp or even a
pulley system to help you get your
prized rock in the back of the truck!
Your Favorite Rock
(actual size)
You
Truck
Simple Machines
• Have few or no moving
parts
• Make work easier
• Can be combined to create
complex machines
• Six simple machines:
Lever, Inclined Plane,
Wheel and Axle, Screw,
Wedge, Pulley
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Lever
Has three parts to it:
1) Fulcrum
2) the load
3) the effort
Trade off: must move
lever large distance
to move load small
distance
• There are 3 types of
levers
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LEVER
1st Class Lever
• The fulcrum is
located between
the effort and the
load
• Direction of force
always changes
• Examples are
scissors, pliers,
and crowbars
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First Class Lever
Fulcrum between effort and resistance.
2nd Class Lever
• The resistance is
located between
the fulcrum and
the effort
• Direction of force
does not change
• Examples include
bottle openers and
wheelbarrows
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Second Class Lever
Resistance between fulcrum and effort.
3rd Class Lever
• The effort is located
between the fulcrum
and the resistance
• Direction of force
does not change, but
a gain in speed
always happens
• Examples include
ice tongs, tweezers,
hammers, and
shovels
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Third Class Lever
Effort between resistance and fulcrum.
Input and Output Forces
• When you use a machine to do work,
you exert a force over some distance.
• For example, you exert a force on the
shovel when you use it to lift soil.
• The force you exert on the machine is
called the input force.
• The machine does work by exerting a
force over another distance, called
the output distance.
Mechanical Advantage
• To do these tasks without a machine would be
difficult.
• We know that a machine multiplies whatever
force put into it (so you can complete the task) :
- Using a screwdriver to turn a screw
- Twisting a nail with pliers
- Carrying a box up a ramp instead
of stairs
• The amount that the machine multiplies that
force is the mechanical advantage of the
machine
• Abbreviated MA
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Mechanical Advantage: Lever
Distance, effort - fulcrum
MA = Distance, load - fulcrum
• What is the MA for the
example?
•Distance from effort to
fulcrum: 10 feet
• Distance from load to
fulcrum: 5 feet
The answer is:
MA = 10/5 = 2
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Inclined Planes
• A slope or ramp that
goes from a lower to
higher level
• Makes work easier by
taking less force to
lift something a
certain distance
• Trade off: the
distance the load
must be moved would
be greater than
simply lifting it
straight up
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INCLINED PLANE
Mechanical Advantage: Inclined Plane
• The mechanical
advantage of an
inclined plane is the
length of the slope
divided by the height
of the plane, if effort is
applied parallel to the
slope
Length of Slope
MA =
Height of Plane
• Let’s say S = 15 feet,
H = 3 feet
So for our plane
MA = 15 feet/3 feet = 5
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Wheel and Axle
• A larger circular wheel
affixed to a smaller
rigid rod at its center
• Used to translate force
across horizontal
distances (like a car)
• Trade off: the wheel
must be rotated
through a greater
distance than the axle
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WHEEL AND AXLE
Mechanical Advantage: Wheel and Axle
Radius of Wheel
MA = Radius of Axle
So for our
wheel and
axle MA =
10”/2” = 5
2"
10"
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Screw
• An inclined
plane wrapped
around a rod or
cylinder
• Used to lift
materials or
bind things
together
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SCREW
Mechanical Advantage: Screw
Circumference of Screwdriver
MA =
Pitch of Screw
Diam.=1"
Circumference = ∏ x 1”
= 3.14”
Pitch = 1/10” = 0.1”
So for our screwdriver
MA =
3.14”/0.1” = 31.4
10 threads
per inch
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Wedge
• An inclined plane
on its side
• Used to cut or force
material apart
• Often used to split
lumber, hold cars
in place, or hold
materials together
(nails)
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WEDGE
Mechanical Advantage: Wedge
Length of Slope
MA =
Thickness of Widest End
2"
• So for our wedge,
MA = 6”/2” = 3
• They are one of
the least efficient
simple machines
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6"
Pulley
• A rope or chain free to
turn around a
suspended wheel
• By pulling down on the
rope, a load can be
lifted with less force
• Trade off: no real trade
off here; the secret is
that the pulley lets you
work with gravity so
you add the force of
your own weight to the
rope
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Mechanical Advantage: Pulley
• The Mechanical
Advantage of a pulley
is equal to the
number of ropes
supporting the pulley
• So for the pulley
system shown there
are 3 ropes
supporting the
bottom pulley
MA = 3
• This means that if
you pull with a force
of 20 pounds you will
lift an object weighing
60 pounds
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The trick is WORK
• Simple machines change the amount of
force needed, but they do not change the
amount of work done
• What is work?
• Work equals force times distance
• W=Fxd
• By increasing the distance, you can
decrease the force and still do the same
amount of work
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Eduardo is helping his family
move out of their old house.
Help him decide which task
would be easier, and then help
him figure out what simple
machine makes the job easier.
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Eduardo has to move some heavy
boxes into the moving truck.
A
B
He would use an Inclined Plane
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Eduardo has to move a heavy
box a long distance.
A
B
He would use a cart with wheels and axles.
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Eduardo needs to tear off a
piece of packing tape.
A
B
He would use a scissors or wedges.
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Eduardo needs to move a heavy box
to his room on the fourth floor.
A
B
He would use a pulley
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Eduardo needs to help his
father move the refrigerator.
A
B
He would use a lever
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Eduardo needs to help his father change
a flat tire on the moving truck.
A
B
He would use a jack that uses a screw.
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Rube Goldberg Machines
• Rube Goldberg machines are
examples of complex
machines.
• All complex machines are
made up of combinations of
simple machines.
• Rube Goldberg machines are
usually a complicated
combination of simple
machines to accomplish a
simple task.
• By studying the components of
Rube Goldberg machines, we
learn more about simple
machines
Safety Device for Walking on Icy Pavements
When you slip on ice, your foot kicks paddle (A),
lowering finger (B), snapping turtle (C) extends neck
to bite finger, opening ice tongs (D) and dropping pillow (E),
thus allowing you to fall on something soft.
Sources
COSI.org. 2006. Simple Machines. Accessed 3 February 2006.
http://www.cosi.org/onlineExhibits/simpMach/sm1.html
Jones, Larry. January 2006. Science by Jones: Levers. Accessed 2
February 2006.
http://www.sciencebyjones.com/secondclasslevers.htm
Mikids.com. 2006. Simple Machines. Accessed 2 February 2006.
http://www.mikids.com/Smachines.htm
Professor Beaker’s Learning Labs. August 2004. Simple Machines:
inclined planes. Accessed 2 February 2006.
http://www.professorbeaker.com/planefact.html
Wikepedia. Accessed 3 February 2006.
http://en.wikipedia.org/wiki/Mechanicaladvantage
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Image Sources
<http://etc.usf.edu/clipart>
<http://www.oz.net/~peragine/doorknob.jpg>
<http://www.theteachersguide.com/clipart/scissors.gif>
<http://www.weprintcolor.com/stockimages/construction/images/Bl
ack%20metal%20crowbar.jpg>
<http://67.19.222.106/military/graphics/flagpole.jpg>
<http://www.morris.umn.edu/UMMimages/public/images/campus_mi
sc/flagpole.jpg>
<http://www.phillips-screw.com/images/homeMain.jpg>
<http://mws.mcallen.isd.tenet.edu/mchi/ipc/ch15htm/images15/Scr
ew.jpg>
<http://www.discountramps.com/handi-van_ramp.gif>
http://staff.harrisonburg.k12.va.us/~mwampole/1resources/simple-machines/flag-pole.jpg
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Images Sources (cont.)
<http://www.physics.uwaterloo.ca/demo/bikewheelgy
ro.html>
<http://www.piratescave.co.uk/about_us.htm>
<http://staff.harrisonburg.k12.va.us/~mwampole/1resources/simple-machines/handicap-ramp.html>
<http://library.thinkquest.org/J002079F/wedge.htm
>
<http://www.idahoptv.org/dialogue4kids/season7/sim
plemachines/facts.html>
<http://www.scienceclarified.com/Io-Ma/MachinesSimple.html>
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