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Monday, December 19, 2011

Feel the Force!

Here's an experiment you can easily do which will teach you something important about second-class levers.

What you'll need:
12-inch ruler
Object that will sit on the ruler without falling off (for example, bag of beans, tape dispenser, glob of clay)

Find a flat surface like the top of a table, desk, or counter. Make sure that it's OK for you to put tape on the surface. Tape one narrow end of the ruler down so that it won't move; this is the fulcrum. You should be able to grab the other end and move is up or down. Place your object (the load) on the ruler very near the fulcrum, then try lifting up the other end of the ruler. Is it easy or hard? Put the ruler back on the surface, and move the object to the end near your hand (the effort). Try lifting the other end. Is it easier or harder than lifting when the load is near the fulcrum. Try moving the object to a few other spots between the fulcrum and the load. Does the effort seem to depend on the position of the load?

You have discovered the law of the lever, which states that, when the the load is closer to the fulcrum than the effort, it will be easier to lift. The lifting gets harder, the farther away the load gets from the fulcrum. The lever law applies to all classes of lever; we've just showed an example of how it applies to a second-class lever. You can make your own first-class lever and test the lever law with it!

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