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kinematics language



Hugh Haskell writes
"Thus if I say this number is
decreasing, and it happens to be negative, the students will
understand that I mean, "getting more negative," in other words, it's
magnitude is increasing, but its sign is negative, so decreasing just
means the final number is more negative than the beginning number."

paul o johnson writes
"If I say that the vector is decreasing, what else can I mean other than
that the magnitude of the vector is decreasing?"

In a post sent a few hours earlier than those where the above two statements
were made, John Denker wrote
"A velocity can't increase for the same reason a velocity
can't be negative. Some component of the velocity in
some arbitrarily-chosen basis might be increasing, but
that is not the same thing."

I think we should all re-read John's e-mail and file it in an easily
accessible place so that we can read it whenever we plan a course involving
kinematics.

I hope Bob Beichner will make the points John Denker raises in this context
central to his approach in his text.

Brian McInnes