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 Quote by grajee All, I have to teach One Dimensional, Two Dimensional, and Three Dimensional Motions to my son and have been reading quite a bit on these topics. I still have a question and would be glad if someone can help me understand or point me in the right direction. I'm worried that I might be missing something very basic. I understand that One Dimensional motion is motion along a straight line and most of the cases, for simplicity sake, it is assumed that the motion is on the X – Axis or Y – Axis or the Z – Axis. In this case, if the motion is on the X-Axis, the Y and Z values will be 0 with X being the only Dimension. But consider the case of a motion along a straight line which is SLANTING and for simplicity sake let us assume that the slant is 45 deg. In this case, though the Z values are 0, the Y values are not, infact the (x,y) values will be (1,1)(2,2)(3,3)(4,4) … etc. So, should this motion not be classified as a Two-Dimensional motion because there are two dimensions (x,y) involved? Why is even this type of motion classified as a One-Dimensional? I understand the coordinate system can be changed by rotating it 45 degrees. But this rotation would also rotate the SLANTING line, correct? In which case, the SLANTING line will always be in between two co-ordinates. Thanks, Gopi
I don't understand that last part of your post.

Nature doesn't care how we orient our coordinate axis. If you have something pointing along the North Star, and your coordinate axes are in such a way that it is in the xy plane, rotating your axes so that that direction is now along the x-axis does NOT simultaneously rotate the direction pointing to the North Star! Nature doesn't know, and doesn't care, that you just did a rotational transformation.

Zz.