MadSci Network: Engineering
Query:

Re: Can u give me examples of differnt kinds of levers??

Date: Fri Oct 13 12:32:48 2000
Posted By: Michael Pantiuk, Grad student, Mechanical Engineering, University of Maryland, Baltimore County
Area of science: Engineering
ID: 970688373.Eg
Message:


Dear Sara:

I must say, that at first I was a little confused by your question.  A
lever is a lever, and there can be only one!  But after thinking about it a
little, (and nosing around on the web) I began to understand what your
meant, and also your confusion.  (which was mine, too, at first!)   So
let's forget rules and types for a bit and try to understand what a lever
is, exactly.

A lever is, quite simply, a way to do work.  You move one end and another
end moves.  Since you don't get something for nothing in this world, you're 
only going to get as much work out of a lever as you put into it.  That is
the key concept to understanding levers.   Not so bad, is it?

So how does a lever work?  You are correct that there are three key items
to a lever:  the fulcrum, the ``force'', and the ``resistance''.  Saying 
``force'' and ``resistance'' are part of the lever is a little confusing 
because they are not actually part of the lever itself, but we'll get to 
that a little later.   

The fulcrum, or pivot, has one purpose:  to give you something to push 
against.  Without it, you might as well be beating the problem with a
stick. While this may be very personally satisfying, it's not very
effective in getting work done.  

The ``force'', as you call it, is simply the work you put into the system.
The ``resistance'' is the work you get out of the system.  Since you seem
familiar with the ``rules'' of levers, I won't bore you with details of how
they relate to each other, I just wanted to give you another way of
thinking of things that might help.


An excellent description of the so-called types of levers can be found at

 http://beakman.com/lever/lever.html


but it it simple enough to say that the only thing that is different
between these types of levers is where the force is applied and where the
work is done in relation to the fulcrum.  The exact same rules apply for
all types, it's just that you're looking at different parts of the lever.  

As for your specific question about a baseball bat, I can see your
confusion.  A baseball bat, by itself, isn't a lever, it's a stick.  But
when you pick it up in your hands and swing it, it becomes a lever.  How? 
Your shoulders become the fulcrum (the thing the lever swings around), the
baseball becomes the resistance (the thing you're trying to move), and your
muscles supply the force.  In the words of the website I mentioned above,
it becomes a 'third class' lever.


I hope this helps you understand things a little bit more!


-m

Michael Pantiuk       mpanti1@umbc.edu
---------------
This calls for a subtle combination of mathematics and extreme violence.




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