What is a shadow and how are they formed?

           A shadow is a region (or space) behind an opaque object where light cannot reach or pass through.  It is the dark area made by an object, blocking the rays of light. Sunlight, or all light sources, travels in waves and if something blocks the path of these waves, a shadow will be formed.

           Some people say that light travels in waves and some people say that light travels in straight lines. The truth is that all of them are correct because light starts as waves but as soon as it crashes into an opaque object it starts to travel in straight lines.

           For a shadow to be formed, you need a light source, an opaque object, and a surface for the shadow to be projected on.