I am writing an academic article but I got confused as I am writing about the weight a specific metal got by using balance scale. Should I use the term mass, which has a unit of kg, or weight, which is a force created by gravity and expressed in N?
5$\begingroup$ As long as your substance never leaves Earth, who cares? $\endgroup$– Ivan NeretinJun 22, 2017 at 14:31
5$\begingroup$ Well, maybe it is about E Musk's travel towards space, Moon, Mars ... $\endgroup$– ButtonwoodJun 22, 2017 at 14:39
4$\begingroup$ If you're being technical, note that amount of matter (or substance) is already a term in its own right. We generally measure this value in moles. $\endgroup$– ZheJun 22, 2017 at 14:53
$\begingroup$ Weight is not expressed in N, but gram or kg. Weight is measured via the gravitational force, but it is not one. A common anglosaxon unit for a force is gf, gram force. Weight and mass use the same units, although they are only identical on the surface of an idealised earth. $\endgroup$– KarlJun 22, 2017 at 21:07
3$\begingroup$ @Karl any physics textbook would say you're talking rubbish. Weight is a force. Force = mass x acceleration. A mass of 1kg weighs 9.8N on earth and 1.6N on the moon, due to the respective gravitational accelerations of 9.8m/s^2 and 1.6m/s^2. If you're going to be a Pedant, get it right. All that said, in nonscientific English (and even in chemistry, where we don't need to make the distinction) it would probably be acceptable to say something has a weight of 1kg instead of a mass of 1kg. In particular, saying "this weighs 1kg" is much less awkward than the more correct "this has a mass of 1kg". $\endgroup$– Level River StJun 22, 2017 at 22:13
Because of the reasoning provided by you, i.e. mass is universal, and weight is the product of mass and magnitude of the local gravitational acceleration, I suggest to stay at mass. (A purist's view, taking @Ivan's comment into account.)
In addition, referring to the International System of Units, their brochure not only mentions the basic units, but the relevant section 22.214.171.124 starts with:
Unit of mass (kilogram)
It's up to you, ultimately. The Wikipedia entry for weighing scales states that:
The balance (also balance scale, beam balance and laboratory balance) was the first mass measuring instrument invented.
A balance or pair of scales using a balance beam compares masses by balancing the weight due to the mass of an object against the weight of a known mass or masses
the balance or pair of scales using a traditional balance beam to compare masses will read correctly for mass even if moved to a place with a different (non-zero) gravitational field strength (but would then not read correctly if calibrated in units of force).
In comparison to a spring balance:
Either type can be calibrated to read in units of force such as newtons, or in units of mass such as kilograms.
Technically, a balance compares weight rather than mass, but, in a given gravitational field (such as Earth's gravity), the weight of an object is proportional to its mass, so the standard "weights" used with balances are usually labeled in units of mass (g, kg, etc.).
1$\begingroup$ I think you have a good reasoning, but with the fact that you had used Wikipedia as a reference source disappointed me. But still, thanks. $\endgroup$– AcidJun 23, 2017 at 9:29
$\begingroup$ Well, the reference is as good as any, and does in fact address the specific issue of using a balance scale, which is not addressed by others. Your query is actually something that will elicit answers that are opinion-based. The first sentence in my answer is the relevant one: it is up to you as the author of the publication. You might get feedback from referees concerning what choice you make. $\endgroup$ Jun 23, 2017 at 12:09
Mass. Weight is mass in a gravity field or acceleration frame.