Definitions of "direction"

While I was in school we were explained (I think it was a physics class) that:

• "direction" is just a line (infinite) between two points, going either way;
• "sense" is the definite way of traveling, either from A to B, OR from B to A, on a certain direction.

I know that in my language "direction" is used (in everyday speech) to encompass both meanings of "direction" and "sense". Is that the same in English?

As example, the Cambridge Dictionary provides the definition:

direction = the position towards which someone or something moves or faces

But I did not find a definition in the restricted sense I mentioned above.

• I'd say that just a line between two points, going either way is a distance. Mar 26, 2019 at 7:58
• "distance" is already another thing, it is the length of the line, not the line. Mar 26, 2019 at 8:53

Direction is, in this context, the orientation someone at the first point would have to be in if they were to be facing the second point.

If you're talking about physics class, I expect the terms would be distance and displacement. Distance is a scalar quantity, the length of a line drawn between two points1, while displacement is a vector quantity, giving both the distance and the direction.

Alternatively, you might be talking about the orientation and sense of a vector. Taken together, those two properties provide the easier idea of direction. The orientation of a vector is an undirected idea of its orientation in space - so a north-south line is the same as a south-north line, because if you superimpose them they are indistinguishable. If you say there are two points on the line, and ask which comes 'first', that is the sense. Taken together, you have a direction. Essentially, a vector is simply a line with magnitude and direction, but that direction can be broken down into the orientation of the vector - up-down, left-right, etc - and the idea of which end of the vector is the 'start'.

I'm not sure there's any free online resources that get into such a technical definition, though.

1: Some teach that distance is the 'distance covered' even if taking a non-direct route, not travelling by a straight line. If you understand distance in that way, then what I have called 'distance' could be called 'straight line distance'. As I was taught it, distance is the length of the straight line, and if you want a term for the length of a wiggly line it would be 'distance travelled'.

• I am surely not talking about distance (straight line, along the road...). I am interested in the meanings: "Along which line?" and "Towards which end of that line.". While entirely correct, I am not sure that this is what I am looking for. I will have to still think about it. Maybe some other answer will bring some different light. Mar 26, 2019 at 10:27
• Okay, I found some more about this... I can see why you might have gotten muddled... Mar 26, 2019 at 10:42
• @virolino: there you go, vector maths explanation. You just got one of the words wrong. Mar 26, 2019 at 10:46
• I am not sure how much "wrong" and how much "false friend", but you are right. The new addition is what I had in mind. Unfortunately, I was not aware enough at the moment to realize that I had to read about vectors. Thank you. Mar 26, 2019 at 10:49