In a political season, momentum is part of the news coverage. Campaigns are always gaining or losing it. Merriam-Webster says momentum is currently in the top 10 percent of word look-ups in its online dictionary.
And the concept is not confined to politics. A quick glance at headlines shows “momentum” an issue for the New York Yankees, for French government officials keen to make the most of the recent “nuke deal” with Iran, and for a supermarket chain struggling to turn itself around.
But what’s the relationship of “momentum” to the moment? How did a word rooted in ideas of weight and speed and physical force morph into a term for a period of time? How did a measure of force become a measure of time?
The Oxford English Dictionary defines momentum as “The quantity of motion in a moving body, now expressed as the product of its mass and its velocity.”
This literal definition is alive and well in the worlds of physics and math, and is the basis for the metaphorical sense, as in the above-mentioned news stories about the Yankees, et al.
That idea of two factors, mass and velocity (speed in a particular direction), is essential. An object without much weight can still produce plenty of momentum – can still pack a punch – if it picks up enough velocity.
This is why security officers on the public observation decks of tall buildings are keen to keep people from dropping, carelessly or otherwise, even small objects over the railing. And it’s also why insurgent political campaigns with small staffs and relatively few supporters are sometimes said to have momentum when they rise dramatically in the polls the morning after a successful debate appearance, for instance.
Both momentum and moment came into English ultimately from the Latin movimentum, a verb meaning “to move.” This explains the physical momentum, but what about the temporal “moment”? The Barnhart Dictionary of Etymology traces moment back to Chaucer, who used it about 1380 to mean a “movement of time.”
The Online Etymology Dictionary, noting a point on which Oxford is silent, says: “Some (but not OED) explain the sense evolution of the Latin word by notion of a particle so small it would just ‘move’ the pointer of a scale, which led to the transferred sense of ‘minute time division.’ ”
Barnhart calls momentum and moment “doublets.” A doublet, according to Merriam-Webster, is “one of a pair; specifically: one of two or more words (as guard and ward) in the same language derived by different routes of transmission from the same source.”
English has lots of doublets. Guard came to English from French, and ward from Old English. But the Online Etymology Dictionary traces both to the Proto-Germanic wardon. Similarly, momentum and moment started out in Latin but followed separate trajectories, to be reunited in contemporary English, like a set of Shakespeare’s shipwrecked twins.