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What are pulleys used for? For industry pulleys , there are a few types of belt options: Timing belt — Contains notched teeth to mesh with the teeth of the matching belt Flat belt — A smooth belt that does not contain notches Round belt — Used to transmit rotational motion around an axle V-belt — Contains an angled track to coincide with the matching belt that passes through What are industry pulleys made of?
As long as we limit ourselves to materials and technologies that would have been available to the ancient Egyptians, it is acceptable for us to use our knowledge to construct pulley systems to build our pyramid. Figure 2. A pulley on a fishing boat. All rights reserved. A pulley is a simple machine consisting of a string or rope wrapped around a wheel sometimes with a groove with one end of the string attached to an object and the other end attached to a person or a motor.
Pulleys may seem simple, but they can provide a powerful mechanical advantage so lifting tasks may be done easily. Pulleys are used in many ways, everyday. What kind of pulleys can you think of? An elevator is a modern engineering use of a pulley system that performs much like the raising of a large stone for pyramid building.
Without the use of pulleys, an elevator would require a large motor to pull the cable straight up. Instead of using a large motor, some elevators use a large weight that takes advantage of gravity to help raise the elevator car see Figure 3.
In this situation, the powering motor can be much smaller and only be used to determine the direction the elevator should go.
Figure 3. Adding a counterweight and two pulleys with a motor in the middle makes an elevator easier to move. But how can a wheel with string over it help us move the huge stones required to build a pyramid? Well, pulleys help us by changing the direction of the force we use to lift an object. Is it easier for you to pull up on a rope or pull down on a rope? By using a pulley, we do not have to pull up on a rope to lift a heavy object attached to it, but instead we can pull down on it.
Think of a flagpole as an example. When you pull down on the rope of a flagpole, the flag goes up the pole to wave in the air. That's because a flagpole has a pulley on it. By using pulleys to redirect force , a stone could be lifted off the ground, allowing more people to grab on to the rope, and adding weight so workers have to pull less.
To simplify this effort even more, workers using a pulley could move a large stone up a ramp by pulling on a rope while walking down the ramp, using gravity to their advantage. The real mechanical advantage of a pulley is in using many pulleys at once.
Using multiple pulleys decreases the amount of force necessary to move an object by increasing the amount of rope used to raise the object. The mechanical advantage MA of a pulley system is equal to the number of ropes supporting the movable load. That means, do not count ropes that are only used for redirecting, see Figures 6 and 7.
We know from other lessons on simple machines that to gain a greater mechanical advantage, there is a trade-off. With a pulley, the trade-off is distance. So, if two pulleys are used together, the amount of force required is cut in half, but twice the amount of rope is needed to be pulled to raise the object to the same desired height.
Illustrate this concept to students by conducting the following classroom demonstration; see Figure 4. Figure 4. Tie the rope to one of the brooms broom 1 and wrap the rope around the other broom broom 2. Have two students stand about a meter apart each holding one broom, and try to keep the brooms separated while the third student pulls on the free end of the rope; it should be a difficult task to pull the broom sticks together.
Next, wrap the rope around each of the brooms again. This is an example showing the power of mechanical advantage. Refer to the associated activity Pulley'ing Your Own Weight to further students involvement in understanding pulley systems by illustrating how a pulley can be used to easily change the direction of a force, making the moving of large objects easier.
Pulleys can be much more complicated. Engineers combine many pulleys into a pulley system that significantly reduces the amount of force required to lift an object. They often use pulley systems to move extremely heavy objects. A block and tackle is an example of a pulley system that can be attached to anything. It may take a lot of cable or rope, but a human using enough pulleys could lift several tons. Engineers use the block and tackle along with motors and electronics to create modern devices that operate with very low power requirements, such as cranes and elevators.
At Disneyland, engineers even use a pulley system to move Tinkerbell across the sky. We are unsure if the Egyptians used pulleys, and have yet to find any evidence that they did, but we do know, that if they had used them, life would have been easier than if they did not. Now, since we understand pulleys and have modern materials, we can build the pyramids much easier. Today we are going to look at engineering a pulley system and see if we can design a way to get our heaviest stones to the top of our pyramid with the help of this simple machine.
Use the Pulleys and the Pyramids PowerPoint presentation as a helpful classroom tool. Show the PowerPoint presentation, or print out the slides to use with an overhead projector. The presentation is animated to promote an inquiry-based style; each click reveals a new point about each machine; have students suggest characteristics and examples before you reveal them.
The pulley, a simple machine, helps to perform work by changing the direction of forces and making easier the moving of large objects. When thinking of pulleys, most people think of the type of pulley that allows a person to redirect the direction of a force. With this type of pulley — called a fixed pulley — pulling down on a rope makes an object rise off the ground.
Roofers may use pulleys in order to hoist all of the shingles up on to the roof instead of attempting to carry them. A crane is a type of pulley that is used in construction.
Engines utilize a pulley system in order to work. Fans with chains are utilizing a pulley system in order to be turned on and off. A bulldozer is an example of use of a pulley system. Pulleys are utilized regularly in oil derricks. Pulleys can be used to extend ladders. Sails on sailboats are raised and lowered using pulleys. Garage doors raise and lower utilizing a pulley system. Rock climbers use pulleys to help them to climb. Mainly attached to a supporting structure, a fixed pulley has a shaft mounted in bearings.
A movable pulley can be easily pulled upwards and downwards. It has an axle in a movable block. Two parts of the same cable support a single movable pulley. It is easier to lift loads effectively by using a movable pulley, as it has a mechanical advantage of two. A compound pulley is a combination of both the fixed and movable pulley that forms block and tackle. Myriads pulleys are mounted on the fixed and moving axle of a block and tackle that aids in fostering the mechanical advantage.
However, compared to a fixed pulley, a pulley manufacturer knows precisely that a movable pulley provides a significant mechanical advantage that determines the efficiency and productivity of a machine. Mechanical advantage implies that the force exerted by the machine is greater than the manual force.
Due to this great advantage, it becomes easier to lift a heavy object with force than the one applied to the cable.
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