# Should we necessarily express the dimensions of a physical quantity within square brackets? [duplicate]

For example, should we write the dimension of mass, e.g. $\mathrm{kg}$ as $[M]$ or is it enough to write it as $M$?

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## marked as duplicate by Manishearth♦Sep 18 '13 at 7:19

Is there a reason you ask? If you just write $M$ it looks like an actual mass, whereas the square brackets make it clear to the reader that you mean "dimension of mass". –  Wouter Aug 4 '13 at 9:32
The reason is for marks in exam... Will the teachers give marks if we write the dimensions without square brackets ? –  Vishnu Aug 4 '13 at 9:44
I would use square brackets on an exam. Not just to make things clear to the reader, but to yourself as well. Personally, I switch between $[M]$ and $\mathrm{kg}$ to denote "dimension of mass" in my own notes. In publications you'd probably want to use the first way, but as I said I use the second way as well in personal notes (consistency with the units is needed then!). –  Wouter Aug 4 '13 at 9:54
@Vishnu: Try mind-reading your teacher's minds . –  Dimensio1n0 Aug 4 '13 at 12:05
It is never worthwhile to dispute a question like this with your instructor. For the purposes of the class the correct answer is the one the instructor told you. –  dmckee Aug 4 '13 at 17:00

One of the best answers to your question is due to the painter René Magritte : http://www.wikipaintings.org/en/rene-magritte/the-treachery-of-images-this-is-not-a-pipe-1948 .

It says: "This is not a pipe." There are several ways for interpreting that statement, questionning the language, the image, or the role of representations.

Another answer is given by Juliet: "What's in a name? that which we call a rose By any other name would smell as sweet". http://en.wikipedia.org/wiki/A_rose_by_any_other_name_would_smell_as_sweet

The story does not say whether Juliet actually smoked the pipe.

The point is that notation, as well as language, is a pure matter of convention for communication with others, as well as with oneself. Depending on established conventions and cultural commonalities, some choices may be better than others. It may also depend on the intended audience willingness to depart from common usage and make some effort to understand you. Parents will do that with children. Examiner may be less willing to do it with students who depart from well established notations or conventions. (What is a "well established notation or convention" ?)

This say, the topic is scientifically very important, as science requires precision in statement. Not just quantitative precision, but also precision in concepts. And sciences develops through communication between scientists.

Some of the progress in science is due to improved notation. The use of a symbol for zero, attributed to Indian mathematicians is the most cited example. The development of positional numeration, such as the decimal system, depends on it. Other progress is also due to evolution of concepts, of new views of existing knowledge, rather than new knowledge itself.

But to keep your concepts clear, just watch out what's in the pipe.

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This is probably the best answer that can be given to this question . –  Dimensio1n0 Aug 4 '13 at 12:07
+1 Somebody has read G.E.D., an eternal golden braid, by Douglas Holstadter. –  ja72 Aug 4 '13 at 12:28

It is just a matter of notation used to distinguish the variable quantity from it's dimension because the two are different,there is no hard and fast rule to it,you can stick to your convention

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He might stick to his notation, but the exam will be graded on the basis of the notation the instructor told him to use... Moreover, there are some fairly common notation conventions out there and the use of square brackets to denote the kind of dimension (rather than a particular unit) is quite common to the point that one could be tempted to use the word "standard". –  dmckee Aug 4 '13 at 16:59
I am sorry but i answered irrespective of whether there is instructor or not,and if you are forced to use instructors notation why do you want an answer here –  Krishna Tripathi Aug 5 '13 at 4:33