Friday, March 9, 2012

Pulleys transfer the direction of force

This week we are taking a look at another one of the six simple machines, the pulley. This will be a two week investigation on pulleys. Pulleys are useful simple machines because they transfer the direction of force needed to lift an object and can give us a mechanical advantage (depending on the type of pulley that is used). There are different types of pulleys: fixed, moveable, and compound, such as the block and tackle pulley. Fixed pulleys are just that - they are fixed in position and do not move except to have their wheel spin. These are usually found on blinds, curtains, flag poles, wells, and on cranes. Moveable pulleys move with the objects they are lifting or moving, such as zip lines, hoists, elevators, cable cars, and sky rides. Moveable pulleys can give a mechanical advantage because it requires less effort to lift or move an object than with fixed pulleys. Like compound words and machines, compound pulleys are made up of two or more pulleys, or pulleys that use two or more wheels. Compound pulleys like a block and tackle pulley can be found on sailing boats, shipping vessels (like fishing boats), tow trucks, and engine hoists.

The students have been exploring some of the different types of pulleys using wooden models. We have also explored the school and found some pulleys that help us with tasks like pulling the American flag up and down the pole each day, opening and closing the curtains on the stage, and opening and closing the blinds (or drawing the blinds across the window). We watched a video clip from PBS's "Sid the Science Kid"series as Sid learns about a simple machine that can help him move some of his toys up to his newly built tree house. (Next week we will watch the conclusion of the video and see some other ideas and examples of pulleys that Sid and his friends and family come up with.) In our journals, we have been drawing some examples of pulley systems and blueprinting the direction of effort used, and how it is being used to make our lives easier.

The fourth and fifth graders started exploring pulley systems using single, double, and triple pulleys, spring scales, and washers. They have been constructing pulley systems to move large washers and investigating the mechanical advantage they get with each system.


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