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Re: Graphing d vs t



At 19:25 -0600 11/12/01, Brian Whatcott wrote:

I get a reassuring sense that Hugh speaks with a voice of quiet reason.
So it is a surprise to find I am with the middle school kids and agin him.

There is only one occasion I know of, when time is a function of something,
and that something is c In that case, I advocate time on the ordinate.

Elsewhere, most anything can only be a function of time, and I see
no great error (excepting the absolutism ) in offering that time occupies
the abscissa.

Thanks for the compliment, and I don't think we are on opposite sides
in this one. I was trying to speak in generalities, suggesting that
it was more rational to arrange your axes in order to get the
information you need from the graph. I agree that that will almost
always put the time on the abscissa, since we are usually interested
in slopes that are with respect to time. I can probably think of some
really obscure occasions when you might want time on the ordinate (I
sure hope you're using those two words right, Brian, because I can
never remember which is which, so I'm relying on you for this one). I
used the middle school example of what I thought was the wrong reason
to demand one variable or another on one axis or another. In too many
experiments we set a variable (the independent variable) and then
measure time (as the dependent variable) merely for convenience,
since measuring time is much easier than controlling time. If we
followed the middle school rule that would demand that time be on the
ordinate, even though reason asks (gently) that it be on the
abscissa. If I read your post correctly, I think that is your
position as well.

When we are dealing with variables other than time, then it is much
easier to make a case for putting any variable on either axis,
depending on what is wanted from the graph. If we want any sort of a
rule, I would argue that it is that the variable on the abscissa be
that with respect to which the slope of the graph represents the
derivative of the quantity on the ordinate.

Peace,

Hugh
--

Hugh Haskell
<mailto://haskell@ncssm.edu>
<mailto://hhaskell@mindspring.com>

(919) 467-7610

Let's face it. People use a Mac because they want to, Windows because they
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