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Machines - Ch. 7

Machines - Ch. 7. I. Introduction to Machines (p.180-183) Machines Force Work Mechanical Advantage. A. Machines. Machine device that makes work easier changes the size and/or direction of the exerted force. B. Force. Effort Force (F e ) force applied to the machine

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Machines - Ch. 7

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  1. Machines - Ch. 7 I. Introduction to Machines (p.180-183) Machines Force Work Mechanical Advantage

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

  3. 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”

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

  5. 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

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

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

  8. 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

  9. 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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