_ is to “momentum” as “speed” is to “velocity”?

Do we have a single word for the magnitude of momentum?
If not, would there be a way to construct one from the root of the word momentum? It’s not coming up in my thesaurus searches, and I’ve never heard of it, but I don’t think it’s actually that uncommon a thing to have to describe, so it seems surprising it doesn’t have it’s own term.

When we write it down it is “|p|”, but it would be very useful to have a terse way to specify this verbally. This is often just referred to as “momentum”, or if there is a need to distinguish “abs-momentum” or “magnitude of momentum”, but does a single word representation exist?

Sample sentence; “The _ of the particle has a lower statistical error than its momentum.”


I will give you the nearest suggestion I can find. That said, I offer it as linguistic curiosity and as illustration for just how rarefied your request is; you should not use it in technical writing because few people will know it. Instead, you should use “magnitude of momentum” or similar phrasing that explicitly specifies what quality of momentum you want.

Birr (OED quoted; most information also in Wiktionary). No, I’m not cold; this Norse-derived term originally referred to wind, but transferred to describing either momentum or force. Its imprecision (not to mention obscurity) is an argument against it:

2a. The force of the wind, or of any moving body; momentum, impetus; rush. to take or fetch one’s birr: to gather impetus for a leap by a short run or ‘ram-race’.

2d. Bodily force exerted against anything, might.

Other words that sometimes convey momentum have similar issues – they are rarely used in that way or they are not specific to magnitude or even momentum. Headway is an example – making headway against a current means keeping forward speed or momentum. None of these usages entered modern scientific writing.

Finally, moment (a word constructed from the root of momentum) means too many things to refer clearly to magnitude. For instance, the moment of momentum is a vector product and should not be used to refer to magnitude alone.

Source : Link , Question Author : Clumsy cat , Answer Author : TaliesinMerlin

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