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Re: transfer of momentum



At 14:38 -0500 11/19/03, Bob LaMontagne wrote:

I agree that negative speed has no more meaning than someone having a
negative height. However, I also dislike the use of 'negative'
velocities. the components of the velocity may be negative, and one
velocity vector can the the 'negative' of another, but there really is
no meaning to a negative velocity - it's not a scalar quantity.

If you limit yourselves to one dimension, then I don't know how else
you can specify direction other than by the algebraic sign on the
velocity. Granted that you can't have a negative velocity in two or
three dimensions, but you certainly see negative Cartesian components
of the velocity, and that's just what you get when you limit yourself
to one dimension.

I don't see anything wrong with doing introductory physics in one
dimension, either. Granted it is a restricted case, but you can teach
all the important principles in one dimension (except circular
motion, but that can be left until later in the course, when they
have absorbed the other stuff and can expand into more than one
dimension), and then when they know more math, and have the basic
ideas down, then you can teach them about vectors in 2 and 3
dimensions without too much trouble, and they will already know how
to handle components, because that's what they have already been
doing, even if they didn't realize it.

I'm a great fan of sneaking good concepts in early without telling
them what you're doing, until afterwards. Then they don't have the
opportunity to get scared of an idea they think might be hard. By the
time they realize they are doing something that's supposed to be
hard, they've already done it. I have frequently gotten the response,
once I told them what they had just done, "You mean that's all there
is to it?" Very satisfying.

Hugh
--

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

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