Levers are basic tools probably used since prehistoric times. They were first described by Archimedes. A lever is a simple machine which makes work easier, which involves moving a load around the pivot or fulcrum using an effort. Watch this video on levers:
http://www.youtube.com/watch?v=wV1pYkTtsxg
In a first class lever, the fulcrum/pivot is in the center of the load and effort. Some examples are the see-saw, scissors and pliers.
In a second class lever, the load is in the middle of the fulcrum/pivot and the effort. Some examples are staplers, wheelbarrows and nail clippers.
In a third class lever, the effort is between the load and the fulcrum/pivot. Some examples are fishing rods, thongs and tweezers.
Sources: http://www.enchantedlearning.com/
http://www.pbs.org/wgbh/nova/teachers/activities/images/27ms_sle2treb_levers.gif
http://www.istockphoto.com/file_thumbview_approve/6952789/2/istockphoto_6952789-fishing-bear.jpghttp://www.pbs.org/wgbh/nova/teachers/activities/images/27ms_sle2treb_levers.gif
http://www.sciencefairprojects-ideas.com/images/stories/seesaw.jpg
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