"Brian Reay" wrote in message
...
NY wrote:
"Tim Streater" wrote in message
.. .
In article , Brian Reay
wrote:

Certainly if you are analysing a problem and checking the dimensions (a
useful technique, not always taught these days although I made a point
of
teaching it), indice notation is probably far easier to use.

I agree about the usefulness of dimensional analysis.

If I can't quite remember a formula, I use dimensional analysis. Is the
dimension that the formula produces different to the dimension of the
answer
that I would expect? Am I adding together terms which are not the same
dimension? If so, check that I've remembered the formula correctly.

v^2 = u^2 + 2 as

m^2.s^-2 = m^2.s^-2 + m.s^-2 . m [ie m^s.s^-2]


So if I had brainfade and mis-remembered it as v^2 = u + 2as, I'd soon
realise that something was wrong.


Likewise with

s = ut + 1/2 at^2

m = m.s^-1 . s [ie m] + m.s^-2 . s^2 [ie m]



Those are good examples.

Dimensional analysis used to be included in Physics, Im not sure if it
was
at O or A level, it is sometimes difficult to recall when you learned
something you seem to have €˜always known. Speaking to a colleague when I
was still teaching, it was included superficially in Physics (I think A
level but possibly GCSE) but he was delighted when he learned I taught it
in my classes.

It goes hand-in-hand with checking that the answer you get is *roughly* what
you'd expect. If you calculate the volume of a hot-water cylinder and you
get an answer of a couple of millilitres (a thimbleful) or a million litres
(a swimming pool) then you've probably made a mistake ;-)