"Natural Science 4" is an interactive encyclopedia that includes scientific information in the understanding of fourth grade students, wonderfully illustrated and animated.
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* Chapter 5 Lesson 28 *
* Shadow and visibility of bodies *
Light is a form of energy that we can see when it reflects on the surface of a body or when we are dealing with a luminous body. We see the Sun, for example, because it produces light, but we see the Moon because it reflects the Sun's light.
The clarity with which we see an object depends on how well it is lit. We will not see objects in a room lit by a candle, for example, as clearly as when the room is lit by an electric bulb. The more intense the light, the more clearly we can see things around us. The visibility of objects also depends on the distance they are from the light source.
Do you remember the story "Human Folly" written by Ion Creangă? One of the peasants was struggling to carry the light to his hut, using a oboro, that is, a kind of wooden bucket. The hiker advised him to cut a window in the wall of the hut and thus the light entered the room by itself. The solution given by the wise hiker is based on the property of light to propagate easily in certain environments.
If light passes through an object easily, we say it is transparent. Glass or clean water is transparent. We can see light passing through a window, but it cannot pass through a wall. This is because the wall is opaque. Opaque bodies do not let light pass through them. Instead, they reflect or absorb light. The outcome? You cannot see what is behind an opaque object.
Colored objects reflect only certain waves of light. The reflected light gives the object the color it has. For example, the rind of a watermelon absorbs all colors except green, which it reflects. Watermelon is opaque because it does not allow light to pass through it.
Objects made of wood, cement or metal are also opaque.
Some objects only partially allow light to pass through them. These are translucent bodies. The outlines of objects behind them can be glimpsed, but not clearly seen. Frosted glass, sunglasses, cloudy water, ice cubes or parchment paper are translucent.
When an opaque object comes between the light source and another surface, a shadow, that is, a dark area, appears to it. The opaque object blocks light, preventing it from reaching that surface. Any bright object, be it the Sun, a light bulb, a candle flame, a campfire or a flashlight, can create shadows. The closer an object is to the light source, the larger its shadow. The shadows cast by the sun change over the course of a day.
Let's say you're standing in front of your home, facing it. Where is your shadow in the morning? What about midday and afternoon? What is the length of the shadow in each situation?