# dynamics: singular or plural

Does the word dynamics take a verb in singular or plural form? In Google search, it looks like both are equally used. For example, which one is more appropriate?

Population dynamics is influenced by a number of factors.

Population dynamics are influenced by a number of factors.

If both are ok, are there any differences in their interpretations?*

"Dynamics" can be either singular or plural, depending on usage. http://i.word.com/idictionary/dynamics

• The science of Dynamics is singular. "Dynamics is important for Physics majors to study."
"Group Dynamics is a useful managerial tool."

• a specific instance of "a pattern or process of change, growth or activity" can be called a dynamic. So in contrasting two or more of these you would use "dymamics" as plural. "Your family dynamic was different from mine." "Our family dynamics were different."

So I would say that your first example refers to the study of population dynamics, whereas the second refers to the varying dynamics of two or more populations.

It is useful to see how "dynamic" and "dynamics" are used in the scientific writings of English-speaking masters and great writers like Maxwell and Truesdell, in a classic like Abraham & Marsden's Foundations of Mechanics, and in the Oxford English Dictionary.

• In The Classical Field Theories and A First Course in Rational Continuum Mechanics Truesdell uses "dynamics" in the following sense (A First Course... p. 6), and as a singular noun:

Mechanics rests upon three substructures: a universe of bodies, a geometry with its kinematics, and a theory of forces. These substructures provide the concepts mechanics is to connect. Relations among places, the shapes of bodies, forces, and times are of two kinds: the general ones, common to all bodies in an assigned universe, appropriate to a branch of mechanics, and the particular ones, which within a given branch distinguish one class of such bodies from another. The general relations are of two kinds: statics, which compares putative equilibria; and dynamics, which describes motions.

So that "dynamics" means the general discipline studying such relations; or sometimes such relations in more restricted contexts, e.g. "dynamics of viscometric flows" (p. 290), or as in the following passage (p. 24):

When it comes to systems of forces, the classical dynamics of mass-points offers a peculiar variant, to which we now turn for the nonce. In describing that dynamics we shall use [...]

He always uses "dynamic" (without final "s") only as an adjective, and never uses "dynamic" or "dynamics" to mean a specific process or motion. For the latter meaning he uses "dynamic process" (p. 198).

• A text scan of the two volumes of Maxwell's Scientific Papers shows that Maxwell also uses "dynamics", as singular noun, as Truesdell does (or I should say, Truesdell does as Maxwell does). The only two possible exceptions are in On physical lines of force, where he says "It remains that we should investigate the dynamics of the system, and determine the forces necessary to produce given changes in the motions of the different parts"; and in On the mathematical classification of physical quantities, where he says "the dynamics of the two systems are different". But again from the contexts it's clear that he's speaking about "general relations", in Truesdell's sense above, not of specific motions or processes. He always uses "dynamic" as an adjective only.

• In Abraham & Marsden's Foundations of Mechanics we again find "dynamics", as a singular noun, in the general sense of Maxwell and Truesdell; except possibly for one passage (p. 424): "the dynamics is generated by the constraints" [italics in the original]. But again from the context I'd personally say that it's meant as a set of possible motions rather than a particular motion.

• If we look for "dynamic" as a noun in the Oxford English Dictionary we are forwarded to "dynamics", except for one meaning: "Energizing or motive force", for which only a couple of poetic, non-scientific examples are given. Under "dynamics" (noun) there is no meaning equivalent to "process" or "motion", though – only the general sense of Maxwell, Truesdell, and Abraham & Marsden.

• Finally, I've never seen the cousin terms "kinematic(s)" or "mechanic(s)" used in the sense of a specific kinematic process or mechanical process. Also, none of the works above ever uses "a dynamic" or "a dynamics".

From the points above I personally would not use "dynamic(s)" to mean a specific process or motion. But language is fluid. If you want to use it to mean a specific process, and you think your readers will not misunderstand you, and you do not care if some of them criticize you for misusing the term... Then why not, go ahead :)

[PS: sorry for the scarcity of links: my "reputation" allows me max two.]

My understanding is that words such as kinetics, dynamics, thermodynamics are nouns and are singular. If they are used without the 's' at the end, they become adjective, such a thermodynamic system, a dynamic enterprise.

I would use "are" in this case, but it wouldn't seem too weird to use "is". It depends on the scenario: If you're talking about population dynamics in general, then you would use "is". If you're talking about a specific case with multiple different dynamics in it, then you would use "are".

• "Dynamics" is not typically plural, just as "hydraulics", "phonics" or "physics" is not typically plural. It can be either, as this shows. books.google.com/ngrams/… Jun 15, 2015 at 7:47
• @BrianHitchcock My mistake - I was assuming that we were talking about a specific instance. Fixed my answer. Jun 15, 2015 at 8:45