Re: Tension, scalar or vector?

In article <[EMAIL PROTECTED]>, Igor 
Khavkine <[EMAIL PROTECTED]> writes
> [EMAIL PROTECTED] (Peter R. Oakfield) wrote in message
> news:<[EMAIL PROTECTED]>...
>
> > Hi. I am in a big argument regarding tension, like in a cord or
> > string. Some knowledgeable people tell me it is a vector; others say
> > it is a scalar. The implications are important. I think it is a
> > scalar, because it has no unique direction and I cannot imagine the
> > meaning of negative tension. Who is right? Could someone please help
> > me?
>
> Tension is a scalar. You can always write the force of tension
> along a rope as T*t.

I.e. the tension is a vector.

> Where t is the unit vector tangen to the rope.
> Since force is a vector and t is a vector, then T, which is the magnitude
> of the tension or just "tension", must be a scalar.

I.e. T is the magnitude of tension, a vector.

> Hmm, negative tension... I don't see a reason why this can't exist,
<snip>
> I would imagine that any configuration of a rope with
> negative tension is unstable, as the rope would prefer to bend itself
> than be in that situation. So in real life they do not occur.

A rope does not support compression. All that means is the 
correspondence between maths and physics breaks down. Try a rod.




Regards

--
Charles Francis