Wednesday, February 8, 2012

Screws versus Bolts

This week we are taking a closer look at one of the six simple machines - the screw. Screws are useful simple machines in that they help us hold things together by applying force through the item or items. They can also take a force that goes around and make it go up and down instead. One of the earliest versions of a screw was invented by Archimedes and used to move water to higher levels in ancient times. Other examples of a screw beyond the kind used to hold materials together are springs, cork screws, and slinkies because they have a spiraling inclined plane wrapped around a central (or imaginary) core. Screws can also be found in nature, especially in shells and shelled animals.

Primary students are comparing screws to bolts using large screws and bolts I found (purchased) at Lowe's, and creating Venn diagrams to help them compare and contrast the two "screws". We have been talking about the ease of installing a screw into a wall because of the wedge on the end whereas a bolt would need to have a hole drilled first. Screws also have their threads (inclined plane) spread wider apart that helps to cut threads into the inside of the hole it is being screwed into; while the threads on a bolt are more standard (to fit nuts on them) and are closer together than on a screw.

The students are able to see how the threads are really one long inclined plane wrapped around and around by taking a paper cut into a right triangle, coloring the angled edge, and then winding it back around itself to make a paper screw.

Fourth and fifth grade students are exploring screws using K'Nex as they construct a hand drill and comparing a drill bit to a screw. They are also learning the mechanical advantages of a screw and how they can calculate the mechanical advantage (MA) by taking length of the spiral and dividing it by the length of the body of the screw (or drill bit, in this case).

For more information on screws as a simple machine, check out these sites:


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