In this explanation, you are going to learn how a shadow forms and why we only see shadows when there is light. When light shines on something that does not let you see through, then a shadow will form on the other side that does not receive the light.
For example, when the sun is shining on you, the sunlight only reaches you from one side, and as a result, a shadow forms on the other side.
If you hold an object on the sun or in a room that has the lights on, you will notice that the object forms a shadow. The object can be a book, a pen, a toy car or anything else. As long as it does not let you see through it, then it will form a shadow on the side that does not receive the light. Objects that do not let you see through are called opaque.
You can have some other projects that let you see through them partly. These objects are called translucent. They behave like opaque objects and at the same time show the characteristics of a transparent thing. A glass window can be transparent or translucent. Other translucent objects include polythene bags, various plastic and glass containers and many document covers.
When light shines on the translucent object, it will still create a shadow on the opposite direction from the light, but the shadow will not be very dark. Very opaque objects create clear dark shadows while those that tend to resemble transparent ones just create a blurry shadow.
Now another thing to note about shadows is their length. Sometimes, shadows will seem very long and at other times, they will be very short. The length of the shadow depends on the position of the light source.
When the light source is almost on a straight light on the side of the object, then the shadow will be very long. As the light source moves towards the top of the object, the shadow becomes shorter, as seen on the bottom surface.
At the same time, you will notice that your shadow created by sunlight is longest in the morning and evening, and when the sun is overhead, your shadow disappears. If asked what it is, you can say that a shadow is an area that the sun can't reach when an object is blocking it.