Transcript SimpleMachines ppt

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Week#10, 2011-12
Students’
Objectives
ESSENTIAL
QUESTIONS,
quotations, &
vocabulary
Announcements,
Questions???,
Review
Teacher presents.
Students do.
Homework ►
 SCIENCE JOURNAL, WEEK #10, Tuesday, Nov. 1
Obj. 6.02 Analyze simple machines
 EQ: What is a simple machine?
 Quotation: “The sleeping fox catches no poultry.”—
Benjamin Franklin
 New Procedure—Binder Up can replace hand. Use it
today.
 Class work assignment in journal? YES
 Frayer diagrams—instructions for simple machines
 CWiJ—Make Frayer Diagrams for 5 machines (Use the
information provided. Follow instructions—two diagrams
per page)
 Revise journal. Box final answer to EQ.
Copy first, then
respond.
Today
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PROCEDURES
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What is this for?
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Can you do this instead?
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If you do this
instead of this
you can continue your work
while you wait for me.
Do this today and at other
times when you must wait.
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,
•Got it?
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• Share information at your table.
• Create your own Frayer diagrams in your own
journal.
• 2 Frayer diagrams per page.
• USE THE RESOURCES AT YOUR TABLE to
find out more, and to help you if you get stuck.
• (e.g. Your resources tell all you need to know to
start learning about mechanical advantage.)
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Copy this template for a Frayer diagram.
Topic
by your name
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FIRST ASSIGNMENT
Use the notes provided to make n Frayer diagrams to tell about any n of
the following topics.
n = ___
•Inclined Plane
•Wheel and Axle
•Wedge
•Pulley
•Screw
•Fixed Pulley
•Lever
•Movable Pulley
•1st Class Lever
•Block and Tackle
•2nd
Class Lever
•3rd Class Lever
•Simple Machines in Your
Body
•Compound Machines
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Make a Frayer Diagram
Inclined Plane
• A flat, sloped surface
• aka: ramp
• How it works: allows you to exert your input force over a
longer distance, thus decreasing input force
• Input force – force with which you push or pull the object
• Output force – force that you would have needed to just lift
the object
• MA = length of incline/height of incline
• The longer the incline, the less input force you need
• fD Fd
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Make a Frayer Diagram
Wedge
• A device that is thick at one end and tapers to a thin edge at
the other end
• One or two inclined planes put together
• Most often used to cut things
• How it works: you move the wedge toward the object, input
force pushes wedge into object and the output force is the
wedge exerting force on the object (e.g. chopping wood)
• MA = length of wedge/width of wedge
• The longer and thinner the wedge, the greater its MA
• fD  Fd
• Examples: hand-held pencil sharpener, shovel blade, knife
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Make a Frayer Diagram
Screw
• An inclined plane wrapped around a cylinder (spiral forms
threads of screw)
• How it works: twist a screw into wood (input force), the
threads increase the distance over which the input force
acts, the threads exert an output force on the object,
friction holds the screw in place
• Input force is decreased by the threads
• MA = length around threads/length of screw
• The closer together the threads, the greater the MA
• fD  Fd
• Examples: bolts, light bulbs, jar lids, some pumps
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Make a Frayer Diagram
Lever
• A rigid bar that is free to pivot, or rotate, on a fixed point
(fulcrum)
• How it works: you exert an input force on one part of the
bar and the other part of the bar exerts an output force on
an object (opening a paint can)
• MA = input arm length/output arm length
• Input arm length – distance from fulcrum to input force
• Output arm length – distance from fulcrum to output force
• Levers can increase/decrease your input force and
decrease/increase the output distance
• Classes of levers – according to the location of the fulcrum
relative to input and output forces
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Make a Frayer Diagram
– First class lever
• Changes direction of input force
• f and d stay same if fulcrum is in center
• Can decrease input force if fulcrum is closer to
output force (e.g. paint-can opener)
• Can increase input force if fulcrum is farther
from output force
• Ex: paint-can opener, scissors (2), pliers (2),
seesaw
• fD  Fd
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Make a Frayer Diagram
– Second class lever
• Does not change the direction of the input
force
• Increases output force
• Ex: wheelbarrow, door, nutcrackers (2),
bottle openers
– (Wheelbarrow also has a wheel and axle.)
• fD  Fd
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Make a Frayer Diagram
– Third class lever
• Does not change the direction of the input
force
• Increases output distance
• lever is attached to fulcrum
• Ex: hockey stick, fishing pole, baseball bat,
catapult
• Fd  fD
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Make a Frayer Diagram
Wheel and Axle
• Simple machine made of two circular or cylindrical objects fastened
together that rotate about a common axis
• Object with larger radius  wheel
• Object with smaller radius  axle
• How it works: apply input force to wheel, axle rotates and exerts output
force
• Increases force, but you must exert your force over a larger distance
• fD  Fd
• Ex: doorknob, steering wheel, screwdriver
• Reverse:
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Apply input force to axle (Fd  fD)
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Ex: transportation vehicles (cars, bicycles)
• MA = radius of wheel/radius of axle
• The greater the difference between the wheel and axle, the greater (or if
reverse situation, lesser) the MA
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Make a Frayer Diagram
Pulley
• A simple machine made of a grooved wheel
with a rope or cable wrapped around it
• How it works: you pull on one end of the rope
(input force), the other end of the rope pulls on
the object (output force)
• Can decrease amount of input force needed (fD
 Fd)
• Can change the direction of input force (d and f
stay same)
• Types of pulleys
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Make a Frayer Diagram
– Fixed Pulley
• Pulley is attached to a structure (pulley does
not move)
• Only changes the direction of the force
• F and D do not change
• MA = 1
• Ex: flagpole, weightlifting machine
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Make a Frayer Diagram
– Movable Pulley
• Pulley is attached to the object you want to
move (pulley moves along rope/cable with
the object)
• Decreases input force needed (fD  Fd)
• MA = number of supporting strands
• Ex: pulleys on sailboats
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Make a Frayer Diagram
– Block and Tackle
• Combines fixed and movable pulleys
• Decreases input force needed (fD  Fd)
• MA = number of supporting strands
• Ex: construction crane
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Make a Frayer Diagram
Simple Machines in the Body
• Most are levers made of bones and muscle
• Muscles pull on bones (input force), joint is
fulcrum, output force is used for doing work
like lifting your hand
• Wedges – your teeth and fingernails
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Make a Frayer Diagram
Compound Machines
• A machine that utilizes two or more simple
machines
• MA = product of MAs of individual simple
machine parts
• Most machines are compound, e.g. apple
peeler, pencil sharpener, bicycle, wheelbarrow,
tweezers, scissors
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