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# 8th Grade Chapter 3 Lesson 6

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### 8th Grade Chapter 3 Lesson 6

1. 1. 8th Grade Chapter 3 Lesson 6 Pgs. 129-137 For Student Use Only
2. 2. Simple Machines • Levers: • 2nd class lever= fulcrum is at end and effort is applied at other end- effort force does not change direction • Ex: wheel barrow, brake pedal • 3rd class lever= fulcrum at end and resistance at the other end- force is applied in between- change speed and distance • Ex: broom, rake
3. 3. Simple Machines • Levers: • Mechanical Advantage: • MA= effort arm/ resistance arm • MA= effort distance/ resistance distance • MA= resistance force/ effort force http://juniorengineering.usu.edu/lessons/machines/images/lever2to1.jpg
4. 4. Simple Machines • Wheel and Axle: • Kind of circular lever • It can multiply force or speed depending on position of effort and resistance • MA= input radius/ output radius http://cache.eb.com/eb/image?id=63036&rendTypeId=4
5. 5. Simple Machines • Pulley: • Simple machine that has a grooved wheel around which a rope or cable passes • May or may not multiply the effort force • Can reverse effort force • Three Types of Pulleys: • Fixed pulley • Moveable pulley • Block and Tackle
6. 6. Simple Machines • Pulley • Fixed Pulley: does not multiply effort force, just reverses it (you pull down, object goes up) • Moveable Pulley: attached to the resistance and moves with it (only half the resistance force, but must move twice as far) • Block and Tackle: moveable and fixed pulleys are used to multiply force and change direction of force
7. 7. Simple Machines • http://etc.usf.edu/clipart/25700/25757/fixed_pulley_25757_md.gif • http://discover.edventures.com/images/termlib/m/moveable_pulley/support.gif • http://cache.eb.com/eb/image?id=6709&rendTypeId=4
8. 8. Simple Machines • Pulley • MA= number of ropes or cables in block and tackle http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/imgmech/pulley.gif
9. 9. Simple Machines • Inclined Plane • Sloping platform that enables an object to move to a higher position without having to lift straight up • Requires less effort to move object this way • MA= effort distance/ resistance distance http://dots.physics.orst.edu/graphics/image_maps/inclined_plane.gif
10. 10. Simple Machines • Wedge • Special inclined plane • Multiples force and changes direction • Used for splitting objects or for lifting objects short distances • MA= length/thickness http://www.brantacan.co.uk/WedgeActionMW.gif
11. 11. Simple Machines • Screw: • Spiral inclined plane • Apply force in the direction of their axis • Applies effort force over a long distance AND resistance over a short distance • MA= 2r/pitch • Pitch= the distance across two of the ridges or threads on the screws shaft • Jackscrew allows people to raise cars or houses
12. 12. Simple Machine • Work Efficiency: • No machine can get 100% efficiency • Efficiency can be increased by reducing friction • Efficiency= work output / work input x 100% • Some machines are very efficient because they have few or no moving parts • Wedge is most efficient simple machine • Friction is important to everyday life!