Date: Fri, 5 Dec 1997 22:03:29 -0800
Message-Id: <v01520d00b0ae19325fb2@[207.204.196.96]>
To: pinhole@exploratorium.edu
From: mafifi@redshift.com (Marc Afifi)
Subject: Re: Vectors
>Wait a minute, before you go any farther I need to correct Mr. Marc
>Afifi comment about the Eq. PE=mgh.
>In this Eq. g is NOT the only vector. If it was then PE (the potential
>energy) would be a vector. The true story is that Work= the dot product of
>two vectors, namely Force and displacement (W=FDcos(alpha)). As a result
>the work is a scalar quantity. And also work = -PE, therefore in the Eq.
>PE=mgh, mg is the force, h is the displacement and the angle alpha is
>either 0 or 180 deg. depending on the direction of motion. If there is
>any questoin, please let me know. A. Rahbar from Louisiana.
Absolutely correct. Thank you A. Rahbar from Louisiana. It was late, I was
tired. I was merely trying to point out that the accelerating force could
only be caused by gravity which we all know pulls radially inward. Since
gravity is providing the force yet the object experiences an acceleration
which is NOT radially inward, then it is perfectly acceptable to use vector
components to aid in the analysis. It is not necessary to choose the
components perpendicular and parallel to the plane, nor is it necessary to
choose only two components. Any combination of vectors whose sum is equal
to g will do. It is merely _convenient_ to choose the normal and parallel
components for ease of calculation. Please correct me if this is also
incorrect.
-Marc
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