Have you ever rubbed your hands together when they get cold? Why do we do that? We do that for friction. Friction happens when two things that aren't very smooth rub together to make heat energy. The faster you rub two things together, the more friction (and heat) you can make. Let's discover friction!

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    Plants are very important. This is because plants can make food from air, water and sunlight. Animals and man cannot make food from air, water and sunlight. Animals can get their food by eating plants and other animals. Man gets his food by eating plants and animals, too. So animals and man need plants in order to live. This is why there are so many plants around us.

    There are two kinds of plants: flowering plants and non-flowering plants. Almost all the trees around us are flowering plants. You can know some trees from their flowers and fruit. Non-flowering plants do not grow flowers. You cannot see many non-flowering plants around you.

    If you look carefully at the plants around you, you will find that there are many kinds of plants. Some plants are large and some are small. Most of them are green. Thanks to the plants around us we can live on earth.

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    Last week, scientists said they discovered a new birdlike dinosaur. With feathers, a beak (鸟嘴) and long legs, it looked pretty funny. This kind of dinosaur was 3 meters (10 feet) long, and it was higher than most humans. It also had sharp claws (爪子).

    Fossil hunters dug out the bones of this species in a rocky place of southwest North Dakota. The scientists nicknamed this dinosaur the "Chicken from Hell". They also gave it a more formal name: Anzu Wyliei. Anzu was a mythical (神秘的) fire-breathing bird. Wylie is the dinosaur-loving grandson of a man who supports the Carnegie Museum of Natural History in Pittsburgh, Pa. Scientists at that museum were part of the team that told the new dinosaur in a paper published on March 19 in the journal PLOS ONE. "The Anzu dinosaur is based on a surprisingly nice specimen(样品), and past digs turned up this animal," a scientist told Science News for Students.

    There's much to see under the sea, but you need to remember that light behave differently in water than in air. The objects appear closer to you than they exactly are. You might find yourself reaching out to touch something and completely missing it.

    Objects under water will appear larger than they would on the surface, too. Be careful not to tell any stories about the big fish that got away. That fish might not be so big after all! It's just because sometimes things can seem to be as much as about 33 percent bigger in water!

    What's more, in deeper water, colors just don't seem as bright. In fact, it looks as if some colors are missing. Remember the color of an object results from the wavelength (波长) of light that are reflected (反射) from its surface. And light is taken in as it moves down through the water.

    Swimmers wear wet suits to keep warm underwater. Let's take a bright red, yellow, and blue wet suit as an example. These colors are hard to miss on the surface of water. Watch carefully the changes in color as you descend in the water. The red part now looks almost black because the red light wavelengths, the longest among these three colors, are missing. As you go down deeper, the same thing will happen to the yellow part and in the end to the blue part. Even at a place of about 6 to 9 meters underwater, you will look terrible, like a ghost(鬼怪) ! And you have to wait for your return to the surface to enjoy the bright colors again!

    More than 1,000 different kinds of pieces of plastic, including 115 cups, 25 bags, four bottles and two pairs of shoes, have been found inside a dead whale(鲸鱼) in Indonesia, according to local officials.

    When the whale was found on the island, it was already decomposing when animal doctors arrived. So they were unable to be sure if the plastic caused its death, said Lukas, the leader of the World Wildlife Fund in Indonesia. The plastic weighed about 6 kilograms, or 13 pounds, he said.

    But pictures of the dead whale caused a warm discussion. The people in the country have started to realize that it is because of using too much plastic. So has the government. Indonesia, a nation of about 260 million people was the world's second-biggest producer of plastic waste in 2018, behind only China.

    If the whales eat too much plastic, they will have a wrong feeling. They think that they are full. And that will lead them to eat less food that provides all the good things they need, said Nicholas who is the leader of the Ocean Conservancy. Moreover, eating too much plastic can make them reduce their weight, their energy and slow down their swimming. As a result, whales are easier to be hurt by the sharks and many other dangerous animals in the sea.

    More than 800 kinds of animals in the sea are affected by about 8.8 million tons of plastic which is thrown away freely in the ocean each year. Plastic can also stop the animals moving freely and sometimes they will cause them to die because they have to be under the water for too long. Some plastic can make a small hole in their stomachs after they eat it.

    Man has a big brain(脑). He can think, learn and speak. Scientists always say that men are different from animals because they can think and learn. They know now that dogs, rats, birds can learn too. They are beginning to understand that men are different from animals because they can speak. Animals cannot speak. They make noises when they are afraid, or angry or unhappy. Apes(类人猿) can understand some things more quickly than humans. One or two of them can learn a few words. But they cannot join words to make sentences. They cannot think like us because they have no language(语言). They can never think about the future. Language is a wonderful thing. Man can build a modern world because he has language. Every child can speak his own language very well when he is four or five, but no animals learn to speak. How do children learn it? Scientists do not really know. What happens inside our body when we speak? They do not know. They only know that man can speak because he has a brain.