"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 4 Lesson 21 *
* Properties of water. States of aggregation *
Life on Earth as we know it could not exist without water. More than two-thirds of the Earth's surface is covered by water. About 70% of the human body is water. In the air, water is present in the form of vapors, and the basement hides countless underground waters. It is easy to understand why water is one of the most important elements in our lives.
Have you ever thought that water changes its density depending on the temperature? Ordinarily, water is found in nature in a liquid state, having no color, taste or smell. In other words, water is a colorless, tasteless and odorless liquid. The presence of liquid water is due to the fact that, most of the time and in most areas of the planet, the air temperature is between 0 and 100 degrees Celsius.
When the air temperature drops below 0 degrees Celsius, water freezes, changing its form of aggregation from liquid to solid. As you already know, ice has a lower density than liquid water. So, along with the state of aggregation, the water also changed its density. If, on the contrary, the air temperature is high enough, the water passes from a liquid state to a gaseous state through a process called evaporation. And in this case the density decreases. Water has its maximum density in the liquid state around 4 degrees Celsius.
Even though water is found everywhere around us, it is an exhaustible resource. Therefore, it should be consumed with caution. The largest amount of water is in seas and oceans. It contains a large amount of salts, washed by the rains that fall on land and transported by the hydrographic network. Even if they are not potable, these waters are essential in: transport, leisure, fishing, energy or due to the exploitation of sea salt.
Streams and lakes are also surface water, but they are not salty. They are said to contain "fresh water". It is used as drinking water, for bodily hygiene and living spaces, food preparation, plant irrigation, in hydropower plants, to obtain electricity, in industry.
The water table, that is, the underground water found on the first impermeable layer on the earth's surface, feeds the springs and wells. It is essential for human consumption and contains an important amount of minerals, necessary for the body. Mineral waters and thermal springs are used to treat certain diseases.
In vapor form, water is essential in humidifying the air. The force of water vapor was observed almost 2000 years ago (show image of Heron of Alexandria). It was used by the inventors of the first steam engines, more than 300 years ago. (you can display images of Denis Papin, Thomas Savery, Thomas Newcomen and James Watt)
Solid water gives us the joy of winter sports and games, protects plants from frost, is used in factories to cool engines and, why not, to cool a glass of juice on a hot summer day.
What would be, in your view, a top 5 of the most important uses of water?