Simple Machine:

1. Simple Machine: The Pulley

2. Simple Machine Part of Lever Family • made with a rope, belt or chain wrapped around a wheel. • member of lever family • a modified lever • point in middle of pulley like fulcrum of a lever • rest of pulley is like rigid arm of lever • multiple pulleys used to increase the MA

3. Calculating Mechanical Advantage • Fixed pulley => MA = 1 • moveable pulley = MA≥2 (count # of supporting ropes.) OR • MA = Fo/Fi (Output Force/Input Force)

4. Fixed Pulley • a pulley in which the wheel does not move. • change the direction of the effort force. • does not increase the size of the effort force. • Fo= Fi; therefore, MA =1. • Li = Lo; therefore, MA = 1

5. Fixed Pulley - 1st class lever with an IMA of 1 - Changes the direction of force 10 lb 10 lb

6. Movable Pulley - 2nd class lever with an IMA = 2 (count the supporting cables) - Force directions stay constant 5 lb 5 lb 10 lb

7. 10 lb 10 lb 20 lb 20 lb 40 lb 40 lb 80 lb Pulleys In Combination Fixed and movable pulleys in combination provide mechanical advantage and a change of direction for effort force. Movable pulleys in combination provide mechanical advantage without change in effort force direction. 800 lb

8. Moveable Pulley • does not change direction of the input force • does increase the size of the force • pull on the rope, pulley & load come up • MA = counting # of ropes that lift load. Typically MA > 2.

9. Pulley System • is simply a fixed & moveable pulley put together. • MA = to the number of supporting ropes. • Typically MA≥3

10. Pulley • redirects tension in a rope, which remains constant in system, thus creating advantage. • more pulleys added =greater MA • each pulley splits amount of force necessary to lift object.

11. Example of Pulleys • http://library.thinkquest.org/27948/pulley.html?tqskip1=1&tqtime=1008

12. Mechanical Advantage • Fixed Pulley: MA = 1 • Moveable Pulley: MA ≥ 2 • Count # of supporting ropes • Fo/Fi

13. MA(pulley) – Example #1

14. MA(pulley) – Example #2

15. MA(pulley) – Example #3 MA = 4

16. Eureka: Pulleys • http://www.youtube.com/watch?v=TlPWy7qW7oM

17. Question #1 A system of pulleys allows a mechanic to lift an 900 N car. a. If the mechanic exerts a force of 300 N on the pulley system, what is the mechanical advantage of the machine? b. What is the mechanical advantage of the pulley system if the mechanic must exert 500 N of force to lift the car? c. After improving the design of his pulley system, the mechanic can now lift the engine with a MA of 4. How much force is now required to lift the engine?

18. Question #2 A system of pulleys allows Kartik to lift an 1400 N elephant. a. If Kartik exerts a force of 200 N on the pulley system, what is the mechanical advantage of the machine? b. What is the mechanical advantage of the pulley system if Kartik must exert 900 N of force to lift the car? c. After improving the design of his pulley system, Kartik can now lift the engine with a MA of 5. How much force is now required to lift the engine?

19. Question #3 • How many supporting ropes does a pulley with a mechanical advantage of 6 have?

20. Question #4 • If Faizan does 500J of work using a pulley system and the force exerted is 300 Newtons, then what is the distance travelled?