A shadow is created when light is blocked from propagating due to an object (based here on the example of a bottle). Since light propagates in a straight line, it cannot curve around the object, but is blocked by the object. The area behind the object cannot be illuminated; it is dark. As a result, this area stands out clearly from the brightly lit surroundings, and we see a shadow.
Personal, social and health education (PSHE)
Siemens Stiftung Media Portal