Now I’m not so sure about “normal.” If you are looking at, say, a table, and you speak about motion in the normal direction, one might think this means in the vertical direction. If it is clear that you consider what you are looking at as existing in a vertical plane in front of you, then the normal direction is clearly the one going from front to back of the scene.
Perhaps one could speak of the “recessional” direction, meaning the direction heading away from the observer. I.e., speak of a “recessional” line as opposed to a vertical or horizontal line, or something moving recessionally instead of horizontally or vertically.
Another possibility would be the “distal” direction, or the “proximal-distal” direction or axis.
I’m getting motion sickness.
The correct answer, as I believe has been pointed out, is “horizontal”
There are two horizontal directions, as we apply the term.
If you doubt this, head out to where you can see the horizon in all directions. Stare out and define for yourself what the “horizontal” is from your perspective, and what the vertical is, and what the direction “out in front of you and behind you” is.
Now turn 90 degrees to your right. Suddenly you will find that the horizon is the line that you were looking for a name for, and the vertical is still the vertical.
Now lie on your back and stare up into the sky, and keeping your arms on the ground, point them in any which direction. Which direction is horizontal? Which direction is vertical? You know that you are looking up, so the direction that is “out in front of you” is the vertical, and the horizontal is any direction your arms happen to be pointing, because no matter how you laid them down, they are pointing along a horizon.
That’s how I see it anyway!
[quote=“drewtwo99, post:44, topic:194936”]
The correct answer, as I believe has been pointed out, is “horizontal”
There are two horizontal directions, as we apply the term.
But the point of the original question is that if we consider vertical to mean along one of the three axes of a region we are looking at (the one from down to up), and horizontal to mean along another (the one from left to right), then what do we call the direction along the third axis (from front to back)? We can’t also call it horizontal, this defeats the purpose of distinguishing this axis from the other two, and prevents us from describing a motion or relative position in terms of three components. For instance, we couldn’t say: to get from the table to the chair, go so far (+ or -) in each direction, because we wouldn’t know which direction horizontal is.
What about “broadside”, which can mean “toward a full side of an object?” The horizontal, vertical, and broadside directions.