Water is the most important liquid on Earth. It covers almost 75 percent of Earth’s surface in the form of oceans, rivers, and lakes. All plants and animals need water to live.
Water is made of tiny units called molecules, which are combinations of even smaller units called atoms. A molecule of water is made of two hydrogen atoms and one oxygen atom. The scientific formula for water is H2O.
Water can be found in three physical states: liquid, solid (ice), or gas (steam or vapor). Freshwater boils when it reaches 100° C and freezes at 0° C.
Most of Earth’s water is in the oceans. But water is constantly being recycled. Through a process called evaporation, water moves from Earth’s surface into the air as water vapor. The vapor can form clouds, which make rain and snow. Rain and snow bring water back to the ground again and into lakes, streams, and oceans. Some of the water seeps underground, where it is called groundwater.
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A clock is a device used to tell time. Moving hands on the face of a clock point to the current hour, minute, and second.
There are three main types of clocks: mechanical, electrical, and atomic. All three must have a source of power and a way to display the time.
Mechanical clocks get their power from moving weights or springs. These parts are attached to gears, or toothed wheels. The gears are attached to the hands of the clock.
Electrical clocks get their power from electricity. Some of them have hands. Others have a digital display.
Atomic clocks measure time using the waves of energy given off by atoms. They were developed in the 1950s and are used by scientists in their work.
In ancient times people measured time by watching the position of the sun in the sky. The ancient Egyptians invented a form of clock called a sundial. Sundials cast shadows that move as the day passes.
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There is the world of the Amish people in America. They live without telephones and television, without cars and electricity. Everyone works on farms and travels by horse or on foot. Amish people are the followers of Jacob Amman. This movement appeared in 1693 in Switzerland, but because of the persecution the Amish had to leave Europe and move to America.
In the eighteenth century the Amish people went to America. Since then their lifestyle has not changed at all. They speak a language called Pennsylvania Dutch, or Amish, which sounds like German. They base their life on the Bible. The Amish is called Protestant Old Believers.
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Soap has a very long history dating back to the Babylonian Empire.
Soap manufacturing technology description was found in Mesopotamia on clay tablets relating to approximately 2200 BCE. Egyptian papyrus of the second millennium BC suggests that the Egyptians used soap. It was widely used in ancient Rome. The Persian chemist Al-Razi wrote a manuscript with the recipes of the ancient world. This ancient manuscript was discovered in the 13th century.
In the Middle Ages in England and France bathe soap was a privilege only of the nobility.
The Spanish Queen Isabella of Castile recognized that she used soap only twice in her life: at birth and on the eve of the wedding.
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Rain is the liquid form of water that falls from the sky in drops. Rain fills lakes, ponds, rivers, and streams. It provides the freshwater needed by humans, animals, and plants. Rain is a part of Earth’s endless water cycle.
It may sound a paradox, but it is actually rain that keeps the earth dry. If the moisture was not taken out of the air and formed into clouds, it would condense on every solid surface. We would feel as if we were in a steam bath.
Rain falls almost everywhere on Earth. One of the world’s rainiest places is Mount Waialeale in Hawaii. It rains about 350 days a year there. One of the driest places on Earth is the Atacama Desert in Chile.
The Sahara desert in Africa is very dry. Rain never falls on some parts of it. It is true that clouds pass over those areas and actually drop rain but the rain never touches the ground. The heat of the desert air evaporates the moisture as it falls.
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Clouds are made of water—thousands of gallons of water, floating high in the air. It’s easier to believe this when you know that cloud water takes the form of tiny droplets. The droplets are so tiny that you couldn’t see one if it was separated from all the others. If all these water droplets in a cloud meet a mass of warm air they evaporate – and the cloud disappears! This is why clouds are constantly changing shape.
Sometimes the water droplets join together around tiny pieces of dust in the air. These drops get bigger and bigger as more droplets collect. When they become too heavy to float, they fall.
There are three main kinds of clouds. “Cumulus” refers to the small puffballs or great wooly-looking clouds that are flat on the bottom. “Stratus” are low clouds, usually streaky or without much shape. And “cirrus” are light feathery clouds, like the ones in the photo. Sometimes cirrus clouds are so high, where the air is very cold, that the whole cloud is made of ice.
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January was named after the Roman god Janus, the god of beginnings and of doors and gateways. Janus was represented as having two faces so that he might guard both entrances and exits. This has reinforced the mistaken belief that January was so named because it was the first month of the year. In fact, however, when the ten-month Roman calendar was reestablished about 700 B.C., January was added as the eleventh month and so named because it contained a feast day in honor of Janus. In 153 B.C. it began to be counted, as the first month and January quickly became a popular festival.
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