Shadows occur when light is blocked by something, then a shadow is formed. Light travels in a straight line. When light is obstructed by something, a shadow will appear from the obstructing object. The strength of the light determines the thickness of the object& x27;s shadow, the distance from the light source and the object& x27;s distance to the object cast by its shadow determines the length and shortness of the image if the shadow falls on another object.