Thursday, July 30, 2009

Simple Machines: Screws

We haven't worked to much on school work since it is summer after all, but we did get in some work this week & did some extra work on our Machine Chart for simple machines. The last column we worked on was for Wedges, so this week we continued with Screws.

Screws are a special kind of inclined plane...really, you say? Yes, the threads of the screw go around & around on an incline. Because of these threads, a screw will hold items more firmly than a nail. Try this experiment to see for yourself:

Place a thin piece of wood on top of a thicker piece of wood, then using a hammer, nail the two pieces together. Take two more similar pieces of wood & screw them together with a wood screw. Now try to pull the two pieces apart. You'll find that the screwed pieces are harder to pull apart. It takes longer to screw pieces together than it is to nail, but it is worth the effort.

Screws can also lift & lower things, such as in a piano seat. Spiral staircases are a type of inclined plane called a screw. Screws can make work easier by increasing the amount of work with less force.

Some other objects with screws that you can see added to our chart are: The mason jar, lids, a vise, bolts, drills & corkscrews. Look around your home to see if you can find more examples of the screw.

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