Explain this common observation clearly: If you look out of the window of a fast moving train, the nearby trees, houses etc. seem to move rapidly in a direction opposite to the train’s motion, but the distant objects (hill tops, the Moon, the stars etc.) seem to be stationary. (In fact, since you are aware that you are moving, these distant objects seem to move with you).
This observation can be explained on the basis of relative motion and the concept of angular displacement.
When we look out from a moving train, the nearby objects (trees, houses) are at a small distance from us. As the train moves, the line of sight changes its direction rapidly for these nearby objects. This causes a large angular displacement of nearby objects in a short time, making them appear to move rapidly in the opposite direction to the train's motion.
On the other hand, distant objects (hill tops, the Moon, the stars) are at very large distances. For such distant objects, the change in direction of the line of sight is extremely small for the same displacement of the train. Hence, the angular displacement is negligible, and these objects appear to be nearly stationary. In fact, since we are aware of our own motion, these distant objects seem to move with us.
Explanation
The context provided includes the question statement from NCERT Physics Class 11, Chapter 2 (Units and Measurements). This phenomenon is explained by the concept of relative motion and angular displacement. The key physics principle is that the apparent motion of an object depends on the rate of change of the angle subtended by the object at the observer's eye. For nearby objects, this angle changes rapidly as the observer moves, creating an illusion of rapid opposite motion. For distant objects, the angle changes very slowly due to their large distance, making them appear stationary. This is also related to the concept of parallax discussed in measurements.