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Pulleys and Force All about force and how pulleys can help reduce it September 2010

Pulleys and Force All about force and how pulleys can help reduce it September 2010. Objectives. Pulleys & Force. Learn about pulleys and pulley systems Learn how using multiple pulleys can dramatically reduce required force

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Pulleys and Force All about force and how pulleys can help reduce it September 2010

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  1. Pulleys and Force All about force and how pulleys can help reduce it September 2010

  2. Objectives Pulleys & Force Learn about pulleys and pulley systems Learn how using multiple pulleys can dramatically reduce required force Learn how pulley systems are used in machines and impact everyday life Learn about teamwork and problem solving in groups

  3. Basics of Pulleys: Two orientations Pulleys & Force Movable Pulley Fixed Pulley

  4. Basics of Pulleys Pulleys & Force Compound Pulley The tension in the rope, T, is always the same everywhere Fixed pulley allows for change in direction of applied force Sum of the forces: vertically 2 T = 100 NT = 50 N

  5. Mechanical Advantage Pulleys & Force This movable pulley system has a mechanical advantage of 2 Mechanical Advantage (MA) isthe factor by which a mechanism multiplies the force or torque put into it. Ideal MA: Actual MA:

  6. Work Pulleys & Force Work is the amount of energy transferred by a force acting through a distance Work = Force x Distance A bigger mechanical advantage decreases the force required, but increases the distance over which it must be applied The total amount of work required to move the load stays the same

  7. Efficiency Pulleys & Force The ratio between Actual and Ideal mechanical advantage is Efficiency Frictionless system = 100% Efficiency

  8. Pulleys in the World Pulleys & Force Pulleys have long been used on sailing ships to handle the rigging and move the sails Even with large mechanical advantages, it still takes many people to do the work!

  9. Pulleys in the World Pulleys & Force Pulleys are used in elevators to change the direction of the tension in the cable, reduce power required of lift motor

  10. Pulleys in the World Pulleys & Force Industrial cranes lift large loads for construction and transportation

  11. Measuring Tension Pulleys & Force Spring Scale Calibrate: Hold spring scale at eye-level and turn adjustment screw until the internal indicator is precisely aligned with the top zero line Measure: Create a loop in the end of the rope you want to measure tension in; attach spring scale to loop. Hold the spring scale steady and read off the tension measurement.

  12. Your Turn Pulleys & Force • Groups of 2 • Develop 2 systems to lift a filled soda bottle 10cm with • 1 pulley • 2 pulleys • Build your systems • Measure the distance the soda bottle moves and compare it to the distance you had to pull • What is the actual mechanical advantage? • Measure the force you must exert on the string and compare it to the force that is finally transmitted to the soda bottle • What is the ideal mechanical advantage? • Calculate the efficiency of each system

  13. Your Turn Pulleys & Force • Now join with one other group at your table • Develop 2 different systems to lift a filled soda bottle 10cm with all 4 pulleys • Build both systems • What are their actual mechanical advantages? Ideal? • Which one has a better efficiency? Why do think that is?

  14. Conclusion Pulleys & Force Which system required the least amount of force to lift the bottle? How did this system rank in its mechanical advantage? Do you think the size of the pulley makes a difference in the ideal mechanical advantage? Actual? How could you further increase the efficiency of your most efficient pulley system design? What other engineering problems were solved with pulleys or pulley systems?

  15. Spring Scale www.arborsci.com

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