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Erasers and Pencils



We all learn the importance of friction in how the world works at a very young age.  For me, a Bill Nye video revealed the power and importance of this contact force.  Without it, we wouldn't be able to stand still in one place, driving would be a nightmare, and about everything else in our lives would be completely out of whack, from our electronics to our daily routines.  Today, however, as I was doing homework, I had a realization of friction that, although simplistic, was something I had to share in order to continue the emphasis of friction's importance in how the world works and the life of a physics student.  Without friction, erasers and pencils, and therefore homework and school, would not work or be possible!  I will start with the simpler of the two: erasers.  It seems pretty clear, that erasers work because the force of friction between the paper, eraser, and graphite on the paper causes the eraser to do work on the graphite (hence erasing), and the paper and graphite to do work on the eraser (resulting in eraser shavings and discoloration).  But the more interesting of the two is the pencil.  A pencil, mechanical in this case, is made of a piece of graphite that is held together by some molecular attractive forces determined by composition.  The only reason that a pencil can write is because the friction between the graphite and the page is greater than the attractive forces that hold the graphite together.  The force of friction "wears away" at the graphite, which allows students to write.  In fact, if you observe the paper closely as the pencil writes, you will see tiny shavings that are the paper, which are a result of the force of friction doing work on the pencil.  Crazy, that without friction even the simplest of things, such as doing homework, would not be possible!


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