Systems and Simple Machines, Gr. 3-4

There are some useful ideas for a Systems and Simple Machines unit at the Hot Chalk Lesson Plan page. Another resource is by the Franklin Institute called Spotlighting Simple Machines. It has explanations about the basic kinds of simple machines and some additional well chosen links. 

How Gears Work explains a more sophisticated use of levers. Look at the tools on Gadget Anatomy and see if you can figure out which simple machines make them up. How Stuff Works has a page on how a block and tackle works.
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