Re: Graphing d vs t

[Brian Whatcott <inet@INTELLISYS.NET>]

At 12:45 PM 11/12/01 -0500, Hugh Haskell wrote:
> >...when
> >graphing distance vs time, time was ALWAYS on the
> >horizontal axis.  I thought it depended upon what was
> >being controlled. If I control time and measure distance,
> >then time is on the horizontal axis but if I control
> >distance and measure time than distance should be on
> >the horizontal axis. Any thoughts?



> . Since the usual thing you want from a d vs. t
> graph is a slope that gives velocity, it makes sense to put time on
> the horizontal axis. But in relativity and Feynman diagrams we
> routinely put time on the vertical axis, because we are looking for
> something other than the slope.
>
> Students learn in middle school, and sometimes in their math classes
> that there is something magic about always putting the "dependent
> variable" on the vertical axis and the "independent variable" on the
> horizontal. But often which variable is dependent and which is
> independent is a function of which is easier to measure and which is
> easier to choose, not any sort of causal reason. So I would say that
> how you orient the graph depends on what use you intend to make of
> it, rather than which variable is dependent and which is independent.
>
> Hugh


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.





Brian Whatcott
  Altus OK                      Eureka!