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Chapter 8

Chapter 8. Work and Machines. Lesson 1: Work. Work  when something moves because of a force being applied Work = force x distance Label is newton-meter or joule. Work formula. w f d. Lesson 2: Energy. Energy  ability to do work There are 2 kinds of energy

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Chapter 8

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  1. Chapter 8 Work and Machines

  2. Lesson 1: Work • Work  when something moves because of a force being applied • Work = force x distance • Label is newton-meter or joule

  3. Work formula w f d

  4. Lesson 2: Energy • Energy ability to do work • There are 2 kinds of energy • Kinetic energy in motion • KE = ½ mv² • Potential stored energy • PE = mgh • gravity = 9.8 m/s²

  5. 6 Forms of Energy • Chemical energy  stored in the bonds btw. atoms • Heat energy  moving particles in matter • Mechanical energy  in moving objects

  6. 6 Forms of Energy cont. • Nuclear energy  stored in the nucleus of atoms • Radiant energy  light energy • Electrical energy  causes electrons to move

  7. Energy can be converted from one form to another • Generator device used to convert mechanical energy to electrical energy • Law of conservation of energy energy cannot be created nor destroyed

  8. Lesson 3: Levers • Simple machines tool that makes it easier or possible to do work • Lever bar that is free to turn around a fixed point • Fulcrum fixed point around a lever turns

  9. Levers cont. • Effort force (FE force applied to a machine by the user • Resistance force (FR) force applied to the machine by the object to be moved

  10. 3 Classes of Levers • Based on the position of the resistance, fulcrum, & effort • First-class lever fulcrum is btw effort & resistance • Changes direction of force & can increase force

  11. Examples of class 1 levers include: • Teeter-totter • Scissors • Pair of pliers

  12. Second-class lever resistance is btw effort and fulcrum • Always increases force • Do not change direction

  13. Examples of class 2 levers include: • Wheelbarrow • Crowbar • Nut cracker

  14. Third-class levers effort is btw resistance & fulcrum • Increases distance which cause resistance to move further or faster

  15. Examples of class 3 levers include: • Tweezers • Stapler • Mousetrap • Broom • Hockey stick

  16. Efficiency • A simple machine cannot do more work than the person using it • Machines increase or change the direction of force • If less effort is needed, more distance is needed also

  17. Effort distance & resistance distance • Effort distance (dE) the distance the effort moves • Resistance distance (dR) the distance the resistance moves • Effort distance is greater than resistance distance

  18. Work Input & Work Output • Work input work put into a machine by the user • Work input = FE x dE • Work output work done by a machine against the resistance • Work output = FR x dR

  19. Efficiency • Efficiency = work output work input x 100 FR x dR FE x dE x 100

  20. Lesson 4: Mechanical advantage • Mechanical advantage number of times a machine multiplies its effort force • Mechanical advantage = resistance force effort force • MA = FRFE

  21. Effort Arm & Resistance Arm • Effort arm distance btw the fulcrum & effort force • Resistance arm distance btw the fulcrum & resistance force • MA = effort arm resistance arm

  22. Lesson 5: Other simple machines • Pulley wheel w/ a rope, chain, or belt around it • A single pulley changes direction, not force; ma = 1 • Fixed pulley attached at top • Movable pulley entire pulley & object attached will rise

  23. Pulley cont. • MA of a pulley = number of ropes that pull upward • The easier to lift an object, the more distance you pull on the rope

  24. Inclined Plane • Inclined plane made of a ramp used to lift an object • MA = length of ramp height of ramp • Gradual slant = greater MA, but greater distance • Steeper slant = less MA, but shorter distance

  25. Screw • Screw inclined plane wrapped around a nail • MA depends on distance btw threads • Smaller distance = more MA

  26. Wedge • Wedge 2 inclined planes placed back to back; inclined plane that moves when used • Thick at one end, thinner at the other • Thinner, more gradual wedge = greater MA

  27. Wheel & Axle • Wheel & axle wheel attached to a shaft • Increases the force you apply to the wheel • MA depends on the size of the wheel & thickness of axle

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