In a variation, if both sides of a movable pulley system are fixed and the rope is taut between the fixed points, the system becomes like a wheel and axle because the object can ride along the rope if a force is applied to it for example, a zip line.
Figure 7. A pulley system with a mechanical advantage of two. Figure 8. A pulley system with a mechanical advantage of four because it has four load-supporting rope segments.
Using a system of pulleys can be much more complex and provide a powerful mechanical advantage — greatly reducing the amount of force required to move an object. If one movable pulley is used Figure 6 , the amount of force required to raise the object attached to the movable pulley is cut in half. The pulley system seen in Figure 7 does not change the mechanical advantage from Figure 6, however, it does change the direction of the necessary force.
The trade-off is that the amount of rope required increases and the amount of rope that you must pull to raise the object is also increased. If two fixed pulleys are added to the system and a second movable pulley is attached to the object, the amount of force needed to raise the object becomes one-fourth of the object's weight, and four times as much rope is required see Figure 8 and Pulleys and the Pyramids PowerPoint presentation.
The powerful mechanical advantage of a pulley is in using many pulleys at once. Combining multiple pulleys decreases the amount of force necessary to move an object by increasing the amount of rope used to raise the object. That means, do not count ropes that are only used for redirecting, see Figures 6, 7 and 8.
Watch this activity on YouTube. How can pulleys make our lives easier? Pulleys are powerful simple machines. They can change the direction of a force, which can make it much easier for us to move something. If we want to lift an object that weighs 10 kilograms one meter high, we can lift it straight up or we can use a pulley, so we can pull down on one end to lift the object up. It is much easier to use the pulley because, as long as we weigh more than 10 kilograms, we can just hang onto the end of the rope and take advantage of gravity so our weight provides all the necessary force to lift the object.
Pulleys can also provide us with a mechanical advantage when we use several together and more rope. This process lessens the amount of force required to lift something. While we do not know if pulleys were used by ancient pyramid builders, we know pulleys are an ideal simple machine for many of the tasks required to build a pyramid. In today's highly-technical world, engineers still use pulleys to make difficult tasks easier.
Without them, our lives would be much more difficult. Conduct summary assessment activities as described in the Assessment section. Conclude by finishing the KWL Chart and assigning Word Problems in which students calculate the mechanical advantage of an inclined plane see the Assessment section. In other lessons of this unit, students study each simple machine in more detail and see how each could be used as a tool to build a pyramid or a modern building.
Making the task easier which means it requires less force , but may require more time or room to work more distance, rope, etc. For example, applying a smaller force over a longer distance to achieve the same effect as applying a large force over a small distance. The ratio of the output force exerted by a machine to the input force applied to it. Usually consists of a grooved wheel in which a pulled rope or chain runs.
For example, a wedge, wheel and axle, lever, inclined plane, screw, or pulley. Brainstorming: As a class, have the students engage in open discussion. Remind students that in brainstorming, no idea or suggestion is "silly. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Have them raise their hands to respond.
Write their ideas on the board. Ask the students:. On a large sheet of paper or on the classroom board, draw a chart with the title "Simple Machines: Pulleys. Fill out the K and W sections during the lesson introduction as facts and questions emerge. Fill out the L section at the end of the lesson. List all of the things students learned about pulleys and their mechanical advantages.
Were all of the W questions answered? What new things did they learn? Based off of their observations of an object's motion can a pattern be used to predict future motion? Word Problems: Assess students' understanding of the lesson concepts by assigning the following word problems. Try making a human pulley. You need board, a strong rope and a spot with an overhead support, such as a soccer goal or playground equipment. Wrap one end of the rope around a 2 x 4 or something strong such as a seat from a swing and wrap the other end of the rope around the goal, letting the trailing end hang to the ground.
Allow one child to sit on the 2 x 4 while two other children try to lift them by pulling down on the free end of the rope. Keep wrapping the rope around the goal or support bar until two children can easily lift the sitting child up and down. It may be helpful to start the sitting child from a standing position both feet on the ground. If the students are unfamiliar with a zip line, have them research this on the internet. A zip line is a fun example of a movable pulley.
Challenge more advanced students to calculate the mechanical advantage of using multiple pulleys, requiring division with remainders or fractions. Accessed January 25, However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.
Why Teach Engineering in K? Find more at TeachEngineering. Quick Look. Simple Machines Pulleys. Print this lesson Toggle Dropdown Print lesson and its associated curriculum. Suggest an edit. Discuss this lesson. Curriculum in this Unit Units serve as guides to a particular content or subject area. Wheeling It In! TE Newsletter. Subscribe to TE Newsletter. Summary Students continue to explore the story of building a pyramid, learning about the simple machine called a pulley.
Students perform a simple demonstration to see the mechanical advantage of using a pulley, and they identify modern day engineering applications of pulleys. There are six basic types of simple machines:.
A lever is a simple machine that can move at a turning point. Levers are made with straight, firm objects, such as a board or rod.
It pivots on the turning point, which is called a fulcrum. Levers work by using less force to lift a load. When there is more distance between the force and the load, less force is needed to move the load. Imagine that Jenny and Brittany are playing on a seesaw. If Jenny and Brittany are further apart, it is easier for them to move the seesaw.
However, the closer they are, the harder it becomes. What are Pulleys? A pulley is a machine that is made with a wheel with a groove in the middle, and a rope. The rope is placed in the groove and the ends are connected to the load. When the rope is pulled, it helps us to move loads or change directions of forces.
Simple Machines: Levers and Pulleys. What are Simple Machines? What are Levers? How do they work? Examples Seesaw, tweezers, pliers, crowbar, wheelbarrow, etc. The capabilities of these different lever types provide engineers with an array of choices during the design and selection process of a particular engineering system. A pulley system operates on the principle that a load can be lifted easier by pulling on a rope or cable that is wrapped between a supporting structure and a rigid fixture attached to the load itself.
One extremely common idea — and often a rule of thumb — for a pulley is to calculate its mechanical advantage by counting the number of pulley wheels found in a system. While this practice is generally acceptable, the method does not always provide accurate results. A more precise method for calculating the mechanical advantage of a pulley is by counting the number of ropes or cables which support the load.
Then the mathematical relationship is simply expressed as:. This result may seem unrelated to the general definition of mechanical advantage; however, this machine remains in perfect agreement with the definition once the input and output distances are identified.
From Figure 11, we can see how the input distance, output distance, and number of support lines are related in a pulley system. This is true regarding all pulley combinations: the more support lines attached to the load, the more input distance required to raise the load up to a desired height.
To conclude, we find that the physical geometry of a pulley system requires its mechanical advantage to always be greater than 1 and only in positive integer values; i. Figure The mechanical advantage of a pulley.
Before stating the mechanical advantage of a wheel-and-axle, it is extremely important to remember that the effort is always applied to the wheel, while the load always acts to resists the turning motion of the axle. Then from the general definition, we see the mechanical advantage of the wheel-and-axle depends only on the radius of each, where it can be written as:.
This result informs engineers how the mechanical advantage of a wheel-and-axle may be altered to provide the most efficient results in an engineering system. Typically, engineers configure the wheel-and-axle so its mechanical advantage is greater than 1 to benefit from a magnified torque, such as the case with a steering wheel.
The mechanical advantage of the wheel-and-axle. All simple machines are characterized by their ability to provide mechanical advantage, which allows engineers to design devices to make work easier and more efficient.
Although one machine is not superior to another, each machine provides its own unique and attractive capabilities which are used by engineers for numerous applications.
The lever is capable of quickly increasing either force or distance; the pulley can lift enormous loads over a vertical path; and the wheel-and-axle is used to easily increase an input torque. These three simple machines, combined with the other three inclined plane, wedge and screw , give engineers a set of extremely valuable tools to effectively carry out work. This machine is primarily used to lift heavy loads along a direct vertical path.
Simple machines can exist on their own and are also sometimes hidden in the mechanical devices around you; a device which performs work by increasing or changing the direction of force, making work easier for people to do. This machine is primarily used to magnify a torque supplied by the user. Tally the votes and write the numbers on the board. Give the right answer. Team Competition : Organize the class into small groups of two or three students each and challenge each group to think of where in engineering systems today the lever, pulley and wheel-and-axle can be found.
The group that thinks of the most machines is the winning team. To get full credit, each team must state the engineering device along with the associated simple machine. Examples: Lever: seesaw, balance scales, crowbar, wheelbarrow, nutcracker, bottle opener, tweezers, fishing rod, hammer, boat oar, rake, etc.
Pulley: crane, elevator, flagpole, etc. Wheel and Axle: screwdriver, steering wheel, bicycle gears, doorknob, etc. A complex machine is one that operates by combining two or more simple machines together.
Consider a pair of scissors. The two arms that you squeeze together are levers , while the cutting edges of the blades are sharp wedges.
The scissors were a solution to a real-world problem that was made simple by breaking it down into smaller pieces. The simple machines of a lever and wedge were combined to create an engineering solution.
In groups of two, think about the following complex machines. For each complex machine, list the simple machines that have been combined and where they are found just like the description of the scissors :. Kahan, Peter. Environment: Hand Tools for Trail Work. Las updated June 16, Federal Highway Administration, U.
Department of Transportation. Accessed August 31, Woods, Michael, and Mary Woods. Ancient Machines: From Wedges to Waterwheels. Minneapolis, MN: Runestone Press, However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government. Why Teach Engineering in K?
Find more at TeachEngineering. Quick Look. Simple Machines Pulleys. Print this lesson Toggle Dropdown Print lesson and its associated curriculum. Suggest an edit. Discuss this lesson. Curriculum in this Unit Units serve as guides to a particular content or subject area. TE Newsletter. Subscribe to TE Newsletter. Summary Students are introduced to three of the six simple machines used by many engineers: lever, pulley, and wheel-and-axle.
In general, engineers use the lever to magnify the force applied to an object, the pulley to lift heavy loads over a vertical path, and the wheel-and-axle to magnify the torque applied to an object. The mechanical advantage of these machines helps determine their ability to make work easier or make work faster. Engineering Connection Simple machines are extremely valuable to engineers since they are used to accomplish extraordinary amounts of work with ease. Grades 6 - 8 Do you agree with this alignment?
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