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Machines -

Machines -. I. Introduction to Machines Machines Force Work Mechanical Advantage. Six types of simple machines: 1) Lever : 1 st ; 2 nd & 3 rd 2) Pulley :(fixed pulley & moveable pulley); block & tackle 3) Wheel & Axle : Ex: Doorknob; gears 4) Inclined Plane : Screw; Wedge

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Machines -

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  1. Machines - I. Introduction to Machines Machines Force Work Mechanical Advantage

  2. Six types of simple machines: 1)Lever: 1st; 2nd & 3rd 2)Pulley:(fixed pulley & moveable pulley); block & tackle 3)Wheel & Axle: Ex: Doorknob; gears 4)Inclined Plane: Screw; Wedge 5)Screw: Type of Inclined Plane 6)Wedge: Type of Inclined Plane

  3. Block and Tackle • Uses ropes and pulleys to multiply forces. • Input force-100 lbs • Output force-200 lbs (the weight of the object being lifted) • # of ropes = # of times the force is multiplied. Tension force

  4. # Ropes = MA 100 = 2 50 Two Ropes Input Force=50 lb Output Force=100 lb

  5. Levers • A lever has several different parts. • Fulcrum-fixed point. • Input arm-between fulcrum and force you apply. • Output force-between the fulcrum and the force applied by the lever on the object.

  6. CLASS 1 LEVER Ex: seesaw, hammer, scissors

  7. CLASS 2 LEVER Ex: stapler, bottle opener, nutcracker

  8. CLASS 3 LEVER Ex: fishing rod, tweezers, tongs

  9. Rotating machines have gears and shafts. They act like rotating levers They have teeth so they do not slip. Gears and rotating machines • Smaller gears must turn faster to do the same work as a large gear.

  10. A. Machines • Machine • device that makes work easier • changes the size and/or direction of the exerted force

  11. B. Force • Effort Force (Fe) • force applied to the machine • “what you do” • Resistance Force (Fr) • force applied by the machine • “what the machine does”

  12. C. Work • Work Input (Win) • work done on a machine Win = Fe × de • Work Output (Wout) • work done by a machine Wout = Fr × dr

  13. C. Work • Conservation of Energy • can never get more work out than you put in • trade-off between force and distance Win = Wout Fe × de = Fr × dr

  14. C. Work • In an ideal machine... Win = Wout • But in the real world… • some energy is lost as friction Win > Wout

  15. D. Mechanical Advantage • Mechanical Advantage (MA) • number of times a machine increases the effort force OUTPUT INPUT • MA > 1 : force is increased • MA < 1 : distance is increased • MA = 1 : only direction is changed

  16. Fr Fe MA D. Mechanical Advantage • A worker applies an effort force of 20 N to open a window with a resistance force of 500 N. What is the crowbar’s MA? GIVEN: Fe = 20 N Fr = 500 N MA = ? WORK: MA = Fr ÷ Fe MA = (500 N) ÷ (20 N) MA = 25

  17. Fr Fe MA D. Mechanical Advantage • Find the effort force needed to lift a 2000 N rock using a jack with a mechanical advantage of 10. GIVEN: Fe = ? Fr = 2000 N MA = 10 WORK: Fe = Fr ÷ MA Fe = (2000 N) ÷ (10) Fe = 200 N

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