Here's why:
* Opaque objects: These objects block all light from passing through them.
* Light travels in straight lines: When light encounters an opaque object, it cannot pass through. This creates an area behind the object where light is absent.
* Shadow formation: The area where light is absent behind the object is the shadow.
Think of a tree on a sunny day. The tree blocks the sunlight, creating a dark shadow on the ground beneath it.
