I've observed this loads of times while travelling, in cars, trains,etc.I can't quite put it in words and therefore I've roughly made a diagram to assist my question.Cases

Assume an observer is travelling somewhat fast along a path, which has a wall with black and white stripes at the side. (I observed the effect in this exact setting.)

Now look at Case A, here the observer is moving straight at some velocity, and is observing the stripes towards the front of his viewing field. (i.e. viewing through the windshield of the car.) The viewer, of course, views the stripes approaching him at some speed.

For Case B, the observer is moving with the same velocity as above, but now is looking at the stripes which are directly adjacent to him. (i.e. viewing through the window on the side of the car). These stripes, strangely, seem to be moving at a much higher speed than the stripes in Case A!(Black and White seem like a blur, if they were distinguishable in Case A)

Is this an actual observed effect, or have my observations been wrong? Why do the stripes in the second case seem to be moving faster even though everything is practically the same?


The stripes appear to move faster in Case B because of the angular velocity that they have. In a reference frame centered on the observer, the velocity stripes in Case A is mainly directed radially, which means they do not have much angular displacement (the direction in which one looks in order to observe them doesn't change much). This allows the eye to easily track the stripes and it gives one the time needed to properly resolve the stripes and their size/shape. However, in Case B, the velocity is mostly tangential to the observer, which means that most of the displacement is angular and not radial (the direction you have to look at in order to track a single stripe quickly changes). This requires one's eyes to move quickly in order to follow a single stripe. The rapid motion across the eyes' field of view is interpreted in the brain as faster motion. Faster angular velocities means it's harder for your eyes to move and properly focus on a single stripe, which makes them look more blurred. At a certain angular speed (I don't know the limit as I'm a physicist, not a biologist), the eye can no longer move fast enough to track a single stripe and so it simply sits and watches the stripes zoom by in a blur.

This is all a matter of how fast the eye has to move to follow the object. Far ahead, the eye barely has to move at all and so it can see and follow the object easily. Adjacent objects cover a larger swath of one's field of view, so the eye must move much faster to follow them. That's about it

  • $\begingroup$ Perfect answer. $\endgroup$ – Hritik Narayan Jan 21 '15 at 12:00

The above answer given by Jim is already satisfactory ,but i think so that it could be the matter of our brain which analyzes the displacement of stripes visible to us while moving and tells us that which one is going faster or slower , in case B our eyes can notice larger displacement of stripes in time T and speed S of us than what our eyes can see through windshield in case A in time T and speed S of us, i.e. why we all feel it going faster when the stripes on the divider of the road are nearer to us .


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