A shadow is a dark area where light from a light source is blocked by an opaque object.
It occupies all of the three-dimensional volume behind an object with light in front of it.
The cross section of a shadow is a two-dimensional silhouette, or a reverse projection of the object blocking the light.
Dark image cast by someone or something when interposed between an object and a source of light.
All these also work for eachother as Shadow is to shade and meadow is to mead .shadow is used for many things now a days(modern ) and before now(traditional,classical or olden),because they use it in determining what the time says before and is also used for direction of roads then in the olden days but presently shadow is not use for anything,the only thing is been used for is just for determining time qnd most peoe dont understand it,only help muslim because its helps them in determining when to pray and when not to.
Shadow can be cast when Like dark is nothing but absence of light, shadow is just a darker surface area. The reason why flame often does not make shadow is because it itself is the source of light.
Basically an object that does not allows any light to pass through will form a shadow.
Shadows are formed by light, because if light shines onto an object, and the object blocks the light, the light will go sideways of the object, and therefore, a shadow is formed.
Light can only travel in straight lines and smoke travel zig zag because smoke is also like a shadow,they are both black the different is just that smoke is been gotten from a burn substance while shadow is the absence of light on a subsatance that has a pattern.