Re: [Phys-l] Motion in 1D, vectors and vector components

[Bernard Cleyet <bernardcleyet@redshift.com>]

"How picky should we be?  Is it so incorrect to say "plot v vs t" or "velocity vs time" that it should be avoided?  Even assuming that "v" is the magnitude of velocity - rather than the true vector velocity - is not right, because | v_vector | is always positive, but we are perfectly comfortable plotting negative values on the graph."  


Four dimensional graphs?

bc, thinks Tim has a good point


Folkerts, Timothy J wrote:

> Along with my previous efforts to decide how to write symbols for kinematic parameters, I have also been struggling with how to deal with 1D motion.  The book I am using (Serway) seems to really botch things up.  Basically, the whole chapter about 1D motion uses the word "vector" when they usually actually mean "x-component of the vector".
>
> For example:
> " Average velocity can be either positive or negative."
> " The average velocity is equal to the slope of the graph of position vs time." 
> " The graph of velocity vs time..."
>
> The X-COMPONENT OF VELOCITY can be positive or negative.
> The X-COMPONENT OF VELOCITY is the slope of x vs t.
> The X-COMPONENT OF VELOCITY can be plotted on a graph.
>
> Serway even admits that he botched the treatment of vectors in 1D when he gets to the chapter on 2D: "This simple solution (using signs to indicate direction) is no longer available in 2 or 3 dimensions.  Instead, we must make full use of the vector concept."  In other words, he didn't do things right the first time!
>
> I expect that other books are similar.
>  
>
> How picky should we be?  Is it so incorrect to say "plot v vs t" or "velocity vs time" that it should be avoided?  Even assuming that "v" is the magnitude of velocity - rather than the true vector velocity - is not right, because | v_vector | is always positive, but we are perfectly comfortable plotting negative values on the graph.  
>
> Sticking to "v_x" or "x-component of velocity"  the whole time would seem to solve the problem without being too burdensome to either the instructor or the students
>
>
> I am currently planning:
> 1) to do vectors first from Ch 3 and discuss components of vectors
> 2) to cover 1D motion from Ch 2, but be more careful about the terminology
> 3) to finish Ch 3 and 2D motion.
>
>
> Tim F
>
>  
>
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