"newshound" wrote in message
o.uk...
The notation m s^-2 and kg m^-3 always strike me as perverse: what was
wrong with m/s^2 and kg/m^3? I remember being taught m/s^2, and then
when I changed school to one that did a Nuffield physics syllabus, the
notation changed to kg m^-2 which it claimed to be "better" in some
unspecified way.

I'm inclined to agree.


I disagree. Mainly as the superscripts reduce the risk of mistakes where
there are multiple terms. Eg

kg.m^ˆ’1.s^ˆ’2
kg/m.s^2


As long as you imply brackets according to the standard BODMAS rules - ie
kg/(m.s^2) rather than (kg/m).s^2 - then you'll be OK in either notation. So
in slash notation you put all the units that are multiplied before the slash
and all the units which are divided (ie have a negative index) after the
slash. Accelerations in m/s/s looks absurd but if you parse it as (m/s)/s
then it's obvious that it's a rate of change of speed wrt time; mind you,
even I wouldn't go so far as to quote accelerations that way.

My understanding is that this is why the "simpler" notation is deprecated.
Also it is better when you are typing stuff from scratch. In the old old
days where manuscripts were hand-written and subsequently transcribed by
typists, or you were exchanging hand written calculation sheets with
colleagues the slash notation is slightly easier to read. Especially if
you express the formula as a fraction, with a full horizontal line.

I think the slash notation tends to match more closely how you would say the
units - "metres per second" rather than "metres seconds-to-the-minus-one"
;-) Index notation is for purists (like IUPAC names for organic compounds)
whereas slash notation is for everyday use (like pre-IUPAC names): most
people know that vinegar contains acetic acid, whereas only people who have
studied chemistry will know that its "Sunday School name" is ethanoic acid.
The latter is logical and makes it obvious that it contains an ethyl radical
like ethane and ethanol do, but it's not the common "lay public" name.

At least no-one's perpetrated the ultimate howler: whereas it makes sense to
refer to a volume (kg/m^3 or kg m^-3) in "kilogrammes per cubic metre", it
is ludicrous to refer to an acceleration in "metres per square second". The
former uses a unit of physical linear dimension, and everyone can visualise
an area in square metres or a volume in cubic metres, but "square seconds"
is ludicrous.