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If you sit in a fast moving car on a highway, you will see the objects outside the window moving backwards with respect to you. Assume that your motion is uniform. One would think that all static objects would move backwards with uniform speed.

However, in real, if you sit in the backseat of a van, you will find the background move at a very fast speed from your window. However, if you look through the window of the people sitting in front, the landscape doesn't move as fast. If you carefully follow one part of the landscape (say a stationary patch of grass, or a moving car), you will see it accelerating as it reaches your window.

Why is this so?

P.S. I don't know much physics, so please explain simply.

ghosts_in_the_code
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  • Are you asking why when you look look at an object while moving toward it, the object - relative to you - appears to be moving faster toward you when it is closer than when it is further away? As in: if I'm driving down the highway and I'm approaching a stationary traffic cone in the road, it appears to be moving "toward me" much faster than the stationary mountain 10 miles ahead? – Kyle Arean-Raines Jun 25 '15 at 15:55
  • Possible duplicates: http://physics.stackexchange.com/q/160460/2451 , http://physics.stackexchange.com/q/116425/2451 , http://physics.stackexchange.com/q/130999/2451 , http://physics.stackexchange.com/q/114748/2451 and links therein. – Qmechanic Jun 25 '15 at 15:57
  • If so, as @Ross Millikan says, it's a consequence of geometry and how our brain perceives distances. For example, when I'm 10 feet from the traffic cone, it appears to be much larger than when I'm 100 feet from it. However the mountain, which goes from being 52800 feet to 52710 feet away, does not appear to change much in size. Because one way humans gauge a change in distance is by a change in apparent size, the mountain doesn't seem to Be moving toward me nearly as fast as the cone, even though physics tells us they are moving at the same speed relative to me. – Kyle Arean-Raines Jun 25 '15 at 16:02

3 Answers3

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You are correct that all exterior static object move backwards with uniform speed. The rest is geometry and psychology, not physics. The geometry part comes if you watch a near object and far background simultaneously. If you draw the line from your eye through the near object to the background, it sweeps rapidly backward across the background. One tends to interpret this as the background moving with you and the near object moving rapidly backward.

Ross Millikan
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  • I never thought about that! Does that mean we will be unable to see the same effect, if we removed the far background (hypothetically)? – ghosts_in_the_code Jun 26 '15 at 15:41
  • You probably wouldn't see the same effect if everything outside the van is the same distance from your route of travel. I made a long drive yesterday with mountains in the distance on both sides of the road. It looked like the mountains were moving with us in the direction of travel with everything nearer to us than the mountains moving rapidly backwards. – Ross Millikan Jun 26 '15 at 16:19
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As you are telling to explain simply,take this example.Take a compass.Put its pointed end on a piece of paper.Take the distance between the fixed arm and the free arm(one to hod the pencil)be 1 cm.Hit it and see it rotate and observe its speed.Now,increase the distance between the two arms to 3 cm.Hit it with a same force.You will see that the speed(more specifically the RPM of the free arm)decreases.Why this is so?Because as the radius increases,the circumference of the circular path also increases.So,the compass has to travel a larger distance.As,time=distance/speed we see that time increases with increases distance.As time increases speed decreases as speed=distance/time.Try to take the idea and implement it in your case.Hope you will be able to get the answer to your question why the distant objects appear to move slower than the nearer objects.

Harmonic
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I agree with ross answer .If you are asking what Kyle just commented then perspective view apply here.If we consider 5 points or objects outside window of bus then drawing parallel lines from it to background will give us single point called vanishing point.The objects that passed by the bus in unit time will be equivalent to that vanishing point passing by.It somewhat pschological.

Sikander
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