Why pulley is a simple machine

It was designed by a scientist called Archimedes, who lived on an island called Sicily in Italy. The block and tackle pulley system is several pulleys sharing one fixed axle at the top. This part is known as the block. The block is connected by ropes to another set of movable pulleys at the bottom, also connected to one axle. The movable part at the bottom is called the tackle. Skip to content Simple Machines. What is a machine?

Types of machines. The Inclined Plane. The Wedge. The Screw. The Lever. The Wheel and Axle. The Pulley. Simple machines terms. What is a pulley? What is a pulley simple machine? Types of Pulleys There are three types of pulleys. A movable pulley Movable Pulley In a movable pulley see diagram on the left , a load is attached to the pulley, and both of them can move from place to place.

The Block and Tackle Pulley System A block and tackle is a combination of pulleys and ropes used for lifting heavy loads. With this type of pulley — called a fixed pulley — pulling down on a rope makes an object rise off the ground. There are also movable pulleys and pulley systems. Thousands of years ago, early engineers used pulleys to help with construction and many useful everyday tasks.

Many obelisks were erected using pulleys and wells have pulleys to help retrieve water. Figure 5. A fixed pulley with no mechanical advantage. The most commonly understood concept of a pulley is that it is a simple machine that redirects force.

This means that by looping rope around a pulley and attaching the rope to an object, one pulls down on the rope to raise the object, instead of having to lift the object see Figure 5; imagine raising a flag.

Although this is a helpful and convenient use for pulleys, it has a major limitation: the force you must apply to lift the object is the same amount as if you were just lifting the object without the pulley which is acceptable for raising a flag, but not helpful enough if trying to raise a pyramid stone.

This means that a fixed pulley does not give any mechanical advantage. A fixed pulley configuration is useful for raising an object to a level above your head. Using this type of pulley also enables you to take advantage of gravity. And, by attaching weights to the end of the rope that you pull, you can lessen the amount of force you must apply.

This type of pulley can also be used to balance an object, by attaching objects of equal weight to both sides of the rope, neither object moves. Once a force is applied to either side, the system continues moving in that direction. This kind of pulley system is used in some elevators. The elevator has cable attached to it that goes up, around a pulley, then comes down and attaches to a counterweight. The motor that moves the elevator car uses much less power since the counterweight keeps the elevator balanced.

Figure 6. A movable pulley with a mechanical advantage of two. Another type of pulley is a movable pulley. In a movable pulley system, the rope is attached to a fixed non-moving point, the pulley is attached to the object that you want to move and the other end of the rope is left free see Figure 6.

By pulling on the rope, the pulley moves and the object raises. This type of system is good if you are trying to raise an object located below you to your level.

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.

A pulley is a wheel with a groove along its edge, for holding a rope or cable. Pulleys are usually used in sets designed to reduce the amount of force needed to lift a load.

However, the same amount of work is necessary for the load to reach the same height as it would without the pulleys. The magnitude of the force is reduced, but it must act through a longer distance. Pulleys are usually considered one of the simple machines.