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MACHINES – UNIT 5

MACHINES – UNIT 5. DEFINITION OF MACHINE. ANY DEVICE THAT HELPS PEOPLE DO WORK . IT DOES NOT CHANGE THE AMOUNT OF WORK DONE. WORK CONSERVATION.

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MACHINES – UNIT 5

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  1. MACHINES – UNIT 5

  2. DEFINITION OF MACHINE • ANY DEVICE THAT HELPS PEOPLE DO WORK. • IT DOES NOT CHANGE THE AMOUNT OF WORK DONE

  3. WORK CONSERVATION • MACHINES DO NOT INCREASE THE WORK YOU PUT INTO THEM. THE WORK THAT COMES OUT OF A MACHINE CAN NEVER BE GREATER THAN THE WORK THAT GOES INTO THE MACHINE. • MACHINES ALSO DON’T CHANGE THE AMOUNT OF WORK NEEDED, SO…

  4. HOW DO MACHINES MAKE WORK EASIER? • BY CHANGING SIZE OF THE FORCE NEEDED TO DO THE WORK AND THE DISTANCE OVER WHICH THE FORCE IS APPLIED • BY CHANGING THE DIRECTIONIN WHICH THE FORCE IS APPLIED

  5. SO, WHY DO WE SAY THAT MACHINES MAKE WORK “EASIER”? THERE ARE 3 WAYS THAT A MACHINE CAN MAKE A TASK “EASIER”.

  6. IT CAN MULTIPLY THE SIZE OF THE INPUT FORCE, BUT DECREASE THE DISTANCE OVER WHICH THE FORCE MOVES OUTPUT DISTANCE IS LESS THAN INPUT DISTANCE

  7. IT CAN MULTIPLYTHE INPUT DISTANCE, BUT DECREASETHE SIZE OF THE FORCE. OUTPUT DISTANCE IS MORETHAN INPUT DISTANCE

  8. 3. IT CAN LEAVE BOTH FORCEANDDISTANCEUNCHANGED, BUTCHANGETHEDIRECTIONIN WHICH THE FORCE MOVES.

  9. IN OTHER WORDS…MOST MACHINES MAKE WORK EASIER BY MULTIPLYING EITHER FORCE OR DISTANCE - BUT NEVER BOTH. NO MACHINE CAN MULTIPLY BOTH FORCE & DISTANCE!!! (THIS IS WORK CONSERVATION)

  10. MECHANICAL ADVANTAGE • THE NUMBER OF TIMES A MACHINE MULTIPLIES THE EFFORT FORCE • Formula = OUTPUT FORCE ___________________________________________________________ ie. pulleys INPUT FORCE

  11. THE MECHANICAL ADVANTAGE TELLS YOU HOW MUCH FORCE IS GAINEDBY USING THE MACHINE

  12. WHAT ABOUT OTHER MACHINES • FOR INCLINED PLANES: LENGTH OF INCLINE / HEIGHT OF INCLINE OR… INPUT DISTANCE / OUTPUT DISTANCE • FOR WHEEL AND AXLES: WHEEL RADIUS / AXLE RADIUS OR… INPUT DISTANCE / OUTPUT DISTANCE

  13. WORK TRANSFERS ENERGY • MACHINES TRANSFERENERGY TO OBJECTS ON WHICH THEY DO WORK (INCLUDING YOURSELF) • WHAT’S THE DIFFERENCE IN WORK BETWEEN CLIMBING A MOUNTAIN STRAIGHT UP AND HIKING UP THE GENTLE SLOPE ON THE SIDE?

  14. TWO TYPES OF WORK INVOLVED IN USING A MACHINE • WORK INPUT = THE WORK THAT GOES INTO A MACHINE; EFFORT FORCE EXERTED OVER DISTANCE

  15. WORK OUTPUT = THE WORK THAT COMES OUT OF A MACHINE; OUTPUT FORCE EXERTED OVER A DISTANCE

  16. KEY WORDS

  17. WORK EFFICIENCY (%) • COMPARISON OF WORK OUTPUT TO WORK INPUT • THE CLOSER WORK OUTPUT IS TO WORK INPUT, THE MORE EFFICIENT THE MACHINE. • NO MACHINE IS EVER 100%EFFICIENT…WHY? FORMULA = WORK OUTPUT -------------------------------------------------------------------------------------------------- x 100% WORK INPUT

  18. MACHINE EFFICIENCY PROBLEMS • YOU DO 4000J OF WORK USING A SLEDGE HAMMER. THE SLEDGE HAMMER DOES 3000J OF WORK ON THE SPIKE. WHAT IS THE EFFICIENCY OF THE SLEDGE HAMMER? WORK OUTPUT / WORK INPUT X 100 3000J / 4000J = .75 X 100% = 75%

  19. YOU DO 250J OF WORK USING AN INCLINED PLANE. THE INCLINED PLANE DOES 100J OF WORK ON THE OBJECT. WHAT IS THE EFFICIENCY? 100J / 250J = .4 X 100 = 40%

  20. REMEMBER…MACHINES CAN MULTIPLY FORCE, BUT NOT WORK. YOU CAN’T GET MORE WORK OUT OF A MACHINE THAN YOU PUT INTO IT EVEN IF YOU DO GET MORE FORCE

  21. INCREASING EFFICENCY • ONE WAY TO INCREASE EFFICIENCY OF A MACHINE IS TO REDUCE FRICTION • HOW CAN YOU INCREASE THE EFFICENCY OF A BIKE?

  22. EFFORT • DEFINITION: THE FORCE YOU APPLY TO THE LEVER/MACHINE.

  23. RESISTANCE • THE FORCE THAT YOU AND THE MACHINE ARE WORKING AGAINST. • ALSO REFERRED TO AS THE LOAD. • FOR EXAMPLE, WHEN USING A WHEELBARROW TO MOVE DIRT, THE WEIGHT OF THE DIRT IS THE RESISTANCE.

  24. FULCRUM • THE FIXEDPIVOT POINT OF A LEVER. Fulcrum

  25. L E V E R

  26. LEVER • A RIGID BAR THAT’S FREE TO MOVE ABOUT A FIXED POINT CALLED A FULCRUM Examples: Shovel, nutcracker, seesaw, crowbar, tweezers, fishing pole, door, etc

  27. THE PARTS OF THE LEVER • WHERE IS THE FULCRUM? • WHERE IS THE EFFORT OR FORCE? • WHERE IS THE RESISTANCE?

  28. THREE CLASSES OF LEVERS • THERE ARE THREE CLASSES, OR TYPES, OF LEVERS • FIRST-CLASS • SECOND-CLASS • THIRD-CLASS • A LEVER’S CLASS IS DETERMINED BY WHAT IS IN THE MIDDLE: THE FULCRUM, THE RESISTANCE, OR THE EFFORT.

  29. FIRST CLASS LEVERS • THE FULCRUM IS LOCATED BETWEEN • THE EFFORT AND THE RESISTANCE. Load Effort

  30. SECOND CLASS LEVERS • THE RESISTANCE IS LOCATED BETWEEN • THE FULCRUM AND THE EFFORT.

  31. THIRD CLASS LEVERS • THE EFFORT IS BETWEEN THE RESISTANCE AND THE FULCRUM.

  32. PLEASE TURN TO PAGE 155 IN YOUR TEXTBOOK • FIRST-CLASS LEVER: FULCRUM IS IN THE MIDDLE. • SECOND-CLASS LEVER: RESISTANCE IS IN THE MIDDLE. • THIRD-CLASS LEVER: EFFORT IS IN THE MIDDLE.

  33. WHAT CLASS OF LEVER IS THIS?

  34. WHAT CLASS OF LEVER IS THIS?

  35. FIRST-CLASS X force/ distance SECOND-CLASS X force/ distance THIRD-CLASS force / X distance

  36. How can you affect the mechanical advantage of a lever? If you move the position of the fulcrum & push down on the lever, the box becomes easier to lift. But in order for it to become easier you have to push the lever down a great distance of 1.5 meters to lift the box up a short distance of .5 meters at the other end of the lever. The task becomes easier because it’s a small force but over a large distance which is converted into a large force over a short distance.

  37. WHEEL & AXLE • MADE UP OF TWO CIRCULAR OBJECTS OF DIFFERENT SIZES WITH THE WHEEL AS THE LARGER OBJECT

  38. WHEEL & AXLE • WHEEL IS LARGER SO IT TRAVELS A GREATER DISTANCE. THE FORCE APPLIED TO THE WHEEL IS MULTIPLIED WHEN IT’S TRANSFERRED TO THE AXLE, WHICH TRAVELS A SHORTER DISTANCE. • WHAT HAPPENS IF THE FORCE IS APPLIED TO THE AXLE?

  39. PULLEY • A ROPE, BELT, OR CHAIN WRAPPED AROUND A GROOVED WHEEL

  40. PULLEY • FIXED PULLEYS ONLY CHANGE THE DIRECTION OF A FORCE • MOVABLE PULLEYS CHANGE THE AMOUNT OF THE FORCE • PULLEY SYSTEMS MAY CHANGE THE DIRECTION OF A FORCE AND THE AMOUNT OF THE FORCE

  41. INCLINED PLANE • A FLAT, SLANTED SURFACE

  42. WH INCLINED PLANE WHERE IS THE INPUT DISTANCE? WHERE IS THE OUTPUT DISTANCE?

  43. INCLINED PLANE • MULTIPLIES THE INPUT FORCE, AND DECREASES THE DISTANCE OVER WHICH OUR FORCE IS EXERTED.

  44. WEDGE • IT’S AN INCLINED PLANE THAT MOVES

  45. WEDGE A SMALL EFFORTFORCE IS ABLE TO OVERCOME A LARGE RESISTANCE FORCE.

  46. SCREW • IT’S AN INCLINED PLANE WRAPPED AROUND A CYLINDER TO FORM A SPIRAL

  47. SCREW • IT ROTATES & WITH EACH TURN MOVESA CERTAIN DISTANCE. • IT MULTIPLIES THE EFFORT FORCE BY ACTING THROUGH A LONG DISTANCE.

  48. MECHANICAL ADVANTAGE OF SIMPLE MACHINES Formula = OUTPUT FORCE ___________________________________________________________ INPUT FORCE IF A MACHINE DECREASES THE FORCE YOU USE YOU USE TO DO WORK, YOU CAN FIND THE “IDEAL” MECHANICAL ADVANTAGE WITHOUT KNOWING THE INPUT AND OUTPUT FORCES. BUT, YOU MUST ASSUME THE SIMPLE MACHINE IS 100% EFFICIENT

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