Chapter 3 Section 3

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Chapter 3 Section 3

• Simple Machines

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I. Simple Machines

• A. There are six basic kinds of simple machines
• Lever
• Wheel and Axle
• Inclined Plane
• Wedge
• Screw
• Pulley

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II. Levers

• Lever rigid bar that is free to pivot or rotate
  on a fixed point.
• Fulcrum fixed point that a lever pivots
• How It works increases force, or increase
  distance
• can sometimes changes direction of your input
  force
• B. Ideal Mechanical Advantage Distance fulcrum
  to input force
• Distance fulcrum to output force
• Remember Ideal Represents a frictionless
  environment

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II. Levers

• C. 3 Classes of Levers- differ in position of
  fulcrum, input force, and output force
• 1) First Class Lever- Always changes direction
  of the input force
• If fulcrum closer to the output force, then
  output force increases
• If fulcrum is closer to the input force, then
  lever increases distance
• Examples Scissors, Pliers, Seesaws, Paint can
  opener

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II. Levers
Example of 1st Class Lever
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II. Levers

• 2) Second-Class Levers These levers increase
  force, but do not change the direction of the
  input force.
• Fulcrum at far end of lever with output force
  somewhere between input force and fulcrum
• Examples Doors, Nutcrackers, Old Pop Bottle
  Openers (didnt twist off)

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II. Levers

• Example of 2nd Class Lever

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II. Levers

• 3) Third-Class Levers These levers increase
  distance, but do not change the direction of the
  input force.
• Fulcrum at far end of lever with input force
  somewhere between output force and fulcrum
• Examples Fishing poles, shovels, hockey stick,
  rake
• Third-class levers have an ideal mechanical
  advantage of less than 1.
• What does this mean???

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II. Levers

• Example of 3rd Class Lever

Who rakes leaves in clothes this nice???
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II. Levers
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II. Levers

• 4) Levers of the Body
• neck 1st class
• foot 2nd class
• arm 3rd class

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III. Wheel and Axle

• Wheel and Axle is an axle attached to the center
  of a wheel and both rotate together
• Wheel- circular object with larger radius
• Axle- circular object with smaller radius

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III. Wheel and Axle

• B. How it works wheel and axle increases your
  output force when input force is applied to wheel
• 1) However you must exert your force over a long
  distance
• 2) What if input force is applied to axle?
• Ex Car Axle vs. Screwdriver
• C. Ideal Mechanical Advantage Radius of Wheel
• Radius of Axle

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IV. Inclined Plane

• Incline Plane - flat, sloped surface
• Enables you to exert your input force over a
  longer input distance
• The input force used to push or pull an object
• 2) As a result, the input force needed is less
  than the output force
• The output force is what you would need to lift
  the object without the inclined plane.

Inclined Plane
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IV. Incline Plane

• B. Mechanical Advantage- number of times machine
  increases force
• 1) Ideal Mechanical Advantage Length of incline
• Height of incline
• 2) The longer the incline, the less input force
  you need to push or pull an object

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• Moving a sofa is easier using a ramp. Using a
  ramp only requires a 100-N force to move the
  500-N sofa. Because of friction, no ramp operates
  at its ideal mechanical advantage.

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V. Wedge

• A. Wedge device that is thick at one end and
  thin at the other a type of inclined plane
• 1) Sometimes incline planes placed back to back
  (double headed axe)
• 2) Instead of moving an object along the inclined
  plane, with a wedge, you move the inclined plane
  itself.

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V. Wedge

• 3) Examples Zippers, Axe, cheese grater
• B. Ideal Mechanical Advantage Length of wedge
• Width of wedge
• 1) The longer and thinner a wedge is, the
  greater its mechanical advantage.

Where is the wedge?
Width of wedge
Length of wedge
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VI. Screws

• A. Screw can be thought of as an inclined plane
  wrapped around a cylinder
• Screw thread- forms spiral inclined plane of
  screw
• Input force- When you twist a screw
• Threads- inclined plane to increase the distance
  over which you exert the input force
• Output force- exerted by threads pulling the
  screw inward

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IV. Screws

• B. Ideal Mechanical Advantage- Length Around
  Threads
• Length of Screw
• C. Examples of Screws Bolts, Light Bulbs, Jar
  Lids
• Lids- your small input force is greatly increased
  because of the screw threads

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VII. Pulley

• Pulley made of a grooved wheel with a rope or
  cable wrapped around it
• B. How it Works change direction and/or
  increase output force.
• 1) Input Force- Your pull on one end of rope
• 2) Output Force- At the other end of the rope,
  pulling directly up on the object

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VII. Pulley

• C. Ideal Mechanical Advantage- equal to the
  number of sections of rope that support the
  object
• D. Types of Pulleys 2 basic types of pulleys
• 1) Fixed Pulley pulley attached to a structure
• Ex. Flagpole
• 2) Movable Pulley A pulley attached to the
  object you wish to move
• Ex Construction Crane
• 3) Block and Tackle- fixed pulley and movable
  pulley system combined

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VII. Pulley

• E. Fixed Pulley No change in output force, but
  does change force direction

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VII. Pulley

• F. Movable Pulley Increases the amount of
  output force, it does not change the direction of
  the force

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VII. Pulley

• G. Block and Tackle- Multiplies output force, and
  can sometimes change direction of output force
• Ideal Mechanical Advantage is equal to the
  number of rope sections supporting the object

Compare input force direction with output force
direction with each block and tackle. What is
the mechanical advantage of each block and tackle?
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VIII. Compound Machine

• Compound Machine Is a machine that utilizes two
  or more simple machines.
• Example A gear is a wheel and axle with teeth
  around the wheel
• Two or more gears working together form a
  compound machine.

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VIII. Compound Machine

• B. Ideal Mechanical Advantage IMA of a compound
  machine is the product (multiply) of the
  individual IMAs of the simple machines that make
  it up.

What are the simple machines that make up this
apple peeler?
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VIII. Compound Machine

• Compound Machine Efficiency
• Calculated by multiplying the efficiencies of
  each simple machine together.
• Each simple machine decreases the overall
  efficiency of the compound machine.
• -Why?