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Unknown, 2009
Current format, Unknown, 2009, , Available.
Unknown, 2009
Current format, Unknown, 2009, , Available. Offered in 0 more formats
All people have jobs to do. Some jobs take a lot of energy. Simple machines help people get jobs done without working too hard. There are six kinds of simple machines: inclined planes, levers, pulleys, wedges, screws, and wheels and axles.
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