Data Analysis
Pulley System Performance
A shipyard has many different pulleys and pulley systems in use. The pulleys are used to move large, heavy, fabricated ship sections through the manufacturing process. During an annual safety and performance inspection of three of the company's systems, a facility engineer collected the data shown in the graph. The data give the measured output forces for a range of given input forces.
Using Graphs What system requires the smallest input force to lift a 2500-N load?
Calculating Determine the actual mechanical advantage for each of the systems for a 2000-N input force.
Applying Concepts Which of the three systems shown in the graph consists of a single fixed pulley? Explain how you know.
Inferring Describe what happens to system B's output force as the input force increases above 4000 N. How does this affect the mechanical advantage of the system at higher loads? Offer a possible cause for the performance shown in the graph.
Applying Concepts Using the mechanical advantage value from Question 2, determine the output force of system A for an input force of 8000 N.
Movable Pulley
As you can see in Figure 19B, a movable pulley is attached to the object being moved rather than to a fixed location. If you are pulling up on the rope on the right with a force of 10 newtons, then both sections of the rope pull up with the same force of 10 newtons. Thus, the pulley exerts a 20-newton output force from a 10-newton input force. The movable pulley in Figure 19B has a mechanical advantage of 2. Movable pulleys are used to reduce the input force needed to lift a heavy object. Sailors use movable pulleys to pull in sails, and skyscraper window washers stand on platforms suspended by movable pulleys.
Pulley System
By combining fixed and movable pulleys into a pulley system, a large mechanical advantage can be achieved. The mechanical advantage that results depends on how the pulleys are arranged. The pulley system shown in Figure 19C has four segments of supporting rope. Ignoring friction, each one of the four segments supplies a lifting force as strong as the force you exert on the rope. Thus the output force is four times stronger than the input force. The pulley system has a mechanical advantage of 4. Using pulley systems in combination with other simple machines, large cranes are able to lift railroad locomotives!
How is it possible to achieve a large mechanical advantage using pulleys?
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