Why do dragonflies have four wings? So that they can hover and fly in any direction that they wish. Most insects have two pairs of wings but the second set in some of them have evolved to have a different purpose. Two examples of these are flies and beetles. (I know we are talking about […]
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How does a pressure cooker work? By using high pressure to raise the boiling point of the water. Pressure cookers were invented in 1679 by a French physicist. He was trying to find a way to cook food faster. Cast iron pressure cookers were made in Germany in 1864. Pressure cookers improved through the early
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How does a refrigerator cool food? By transferring the heat from inside the refrigerator to outside using evaporation. Fresh foods have to be kept cool to make them last longer. As soon as they are opened, or cut, bacteria start to decompose them. When foods decompose, they taste bad, but some bacteria can produce toxins
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Why does metal spark in a microwave oven? The microwave charges one side of the metal positively and one side negatively. This charge can ionize the air, making sparks. First, we need to look at what microwaves are. A microwave is a type of electromagnetic radiation. Electromagnetic radiation is energy that moves in waves and
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How long has the Sahara been a desert? Possibly for 4.6 million years, but maybe as long as 7 million years., The Sahara goes through a 41,000-year cycle. The Sahara Desert is the largest hot desert on Earth. The largest deserts are actually the Antarctic and the Arctic deserts. The Sahara is 9.2 million square
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How does crop rotation work? By alternating crops to give the soil a rest and to replace nutrients that are removed. People transitioned from a hunter-gatherer culture to an agricultural culture in about 12000 BC. First, they domesticated animals. This happened in different places on Earth within a few thousand years. In about 9500 BC,
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How does a steam engine work? By taking the energy contained in coal and making heat. Then using the heat to turn water into steam and using the steam to push and pull a piston. The steam engine was the invention that helped push the Industrial Revolution. However, the knowledge of steam power has been
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How tall could a skyscraper be? Theoretically 69.1 km tall, but practically, about 2 km. The tallest building in the world at the moment is the Burj Khalifa. It is 830 meters tall. For over 3800 years, the tallest building in the world was the Great Pyramid at Giza. It was 147 meters tall when
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When did the Egyptian Empire start to decline? It peaked during the reigns of Ramesses II and Ramesses III from 1279 BC to 1155 BC) and then began to decline. People have been living along the Nile valley since about twelve thousand years ago. They were hunter gatherers and fishermen to start with, but they
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Where did the names of the continents come from? Generally, from Greek and Latin. There are seven continents and one continent that is almost completely underwater. In order of size, the continents are Asia, Africa, North America, South America, Antarctica, Europe, and Australia. The submerged eighth continent is Zealandia. The only part of Zealandia that
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