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When travelling by a train, it seems that the nearby objects move in the opposite direction(which I can explain) but the distant objects appear stationary. I can't explain this. By the concept of relative velocity shouldn't all objects appear to move in opposite direction?


marked as duplicate by John Rennie, Danu, DavePhD, jinawee, JamalS Jun 2 '14 at 11:58

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I'm not convinced brightmagus' answer is completely accurate. The real reason is not "perspective", which simply aligns things in your image, but "field of view" (FOV). You see everything in a particular angle (your eye is at the vertex of the angle), and from basic trigonometry the absolute length of the scene you can take in is a function of the FOV and the distance from your eye. Since you are travelling at a fixed rate of speed, you move past a full scene-width close to the train in far less time than a full scene-width far from the train.
To use his numbers: if you're moving at 10 m/s, then for a FOV which covers 10 m at a distance of, say 100 m away (this is rather narrow), you'll see a whole new scene every second. But looking 1 km out, it'll take approximately 10 seconds to move to a whole new scene.


This is all due to perception, and perception is governed here be the phenomenon called perspective. Objects nearby look large and those far away look small. This means that also far away distances (traveled) look smaller than the same distances near you.

A 10-meter distance 1 km away from you is relatively much much smaller than the same distance 2 m from you. A 10 m distance traveled by the train (you are in) appears much larger if you look at trees located 2 meters from the track than when you look at trees located 1 km from the track. Also 10 m distance along a line 2 m away from you is more than your eyes can even encompass, while 10 m distance along a line 1 km away is less then your eyes can discern. That's the whole secret why you can't (easily) see movement when looking far away. The relative changes are simply very tiny.

Now, if you ask why the perspective phenomenon happens at all, the answer is this picture:

enter image description here
(source: vresources.org)

As you can see, because the field of view is a triangle (it is the 3D field that we normally focus on), than the distance you can encompass with your eyes is larger the further it is from you. This also means, however, that relative distances get smaller.