Why do things look smaller when farther away? [duplicate]

Here is my question: Take an object A and another object B, both of the same size.

B is rigid (static) but A is mobile . If I took A further away from observer then it goes on shrinking. Why is that the case ??😶😶

If I understand your question correctly, you wonder why when an object is far away it seems smaller?

This can be explained with basic trigonometry.

In this triangle, let say your object A has a height given by the distance $h=HF$

If we call the distance between your eyes and the object $d=EF$

Then the height that you see is linked to the angle at the corner $E$. Let's call that angle $\theta$.

Then, you have $\theta=arctan(h/d)$

As d gets bigger, the angle $\theta$ will decrease and it will seem that the objects is shrinking.

• bit.ly/22W7ep9 shows a 27 second clip from a TV show called Father Ted, explaining the same point about cows.
– user108787
Aug 6, 2016 at 14:56