basic physics terms

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Hi,(1) Is it true that VELOCITY is always a vector?      In turn, SPEED is only used to refer to scalars?(2) Unlike the pair VELOCITY/SPEED, ACCELERATION can be either vector or scalar, depending on the context within which it's used)?And there are no special terms to distinguish between "vector acceleration" and "scalar acceleration"?(3) There are two points, A and B, in 3D space.DISTANCE and RANGE (between A and B, from A to B) are always scalars?The only way to emphasize you are actually talking about the vector connecting A and B is to use the term RADIUS-VECTOR?Would it be a .... "passable workaround" to use "vector separation", (sic!) "vector range" or (sic!) "vector distance" for the much more popular "radius-vector" (at least in everyday English, not technical writing) ??mus-te

AlpheccaStars · Accepted Answer

MUSCOVITE(1) Is it true that VELOCITY is always a vector? In turn, SPEED is only used to refer to scalars?

Ask your questions in a Physics site, or consult an on-line Physics site such as this one: http://www.physicsclassroom.com/class/1dkin/u1l1e.cfm

We do English grammar here. The grammar of your questions is OK.

MUSCOVITEWould it be a .... "passable workaround" to use "vector separation", (sic!) "vector range" or (sic!) "vector distance" for the much more popular "radius-vector" (at least in everyday English, not technical writing) ??

None of those expressions are "everyday English."

CSnyder · Answer

In a physics context:

1) Yes, velocity is always a vector, and speed is always a scalar.

2) Acceleration is always a vector. It may not explicitly be listed in vector format (i.e. with both a magnitude and direction) if the direction is clear from context (e.g. gravitational acceleration in a uniform field, or uniform circular motion). If something is listed as "acceleration" and you don't know what the direction is supposed to be, ask your instructor.

3) "Distance" is always a scalar. In most contexts, it means the Euclidean distance (the ordinary distance that everyone is familiar with) between two points. In some special contexts it might mean some other distance, but that should be clear from context. I don't think I've ever heard "range" used to mean distance, but if I saw it in a paper I would assume they meant distance.

Yes, the only way in common use to denote the vector pointing from A to B is by saying "the vector pointing from A to B", or "the radius vector from A to B", or (most commonly), R_ab. If you had to use some other term, "vector distance" would probably be best. But remember that you can't just say "the vector between A and B" because you need to know whether the vector points from A to B or from B to A.

MUSCOVITE · Answer

CSnyder -
Thank you so much for your detailed comments!

It is very interesting and important for me to clearly understand possible nuances/differences between the English terms "speed/velocity", "acceleration", "distance" and their Russian counterparts/equivalents. And such curious differences do exist (based on what I just learned from your post)!

For example, I wouldn't say that

CSnyderAcceleration is always a vector. )

Quite the opposite, when my fellows countrymen say "acceleration" (in their mother tongue) they normally mean a scalar characteristic! ...If people need to emphasize they are talking about a 3D acceleration actually , they'll very likely say "vector acceleration", ... unless it's 100% clear from context :-)

CSnyderIf you had to use some other term, "vector distance" would probably be best.

That's yet another interesting difference!
Although "vector distance" can well be used for "radius vector" in English (as you said), the word for word translation of "vector distance" into Russian in never ever used by engineers/scientists here... The only acceptable term would be "radius vector" imho ...

Again, thank you very much for your input!

AlpheccaStars · Answer

MUSCOVITEQuite the opposite, when my fellows countrymen say "acceleration" (in their mother tongue) they normally mean a scalar characteristic! .

Right. If you followed the link in my prior post, you will read that when physicists talk about "acceleration" it is always a vector.

When laymen talk about the acceleration of their souped-up sports car, or the running back on the football team, they generally mean a number -- a magnitude or scalar quantity.

MUSCOVITE · Answer

AlpheccaStars when physicists talk about "acceleration" it is always a vector.When laymen talk about the acceleration of their souped-up sports car, or the running back on the football team, they generally about a number -- a magnitude or scalar quantity.

Understood! Looks like we are all on the same wavelength finally :-) Thank you so much!

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