A satellite is any object that moves in a curved path around a planet. The moon is Earth's original, natural satellite, and there are many man-made (artificial) satellites, usually closer to Earth. The path a satellite follows is an orbit, which sometimes takes the shape of a circle.
To understand why satellites move this way, we must revisit our friend Newton. Newton proposed that a force -- gravity -- exists between any two objects in the universe. If it weren't for this force, a satellite in motion near a planet would continue in motion at the same speed and in the same direction -- a straight line. This straight-line inertial path of a satellite, however, is balanced by a strong gravitational attraction directed toward the center of the planet.
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Замени подчёркнутые слова местоимениями. прочитайте предложения. 1) denis _ross_ is happy. 2)sally_ can see a big ship. 3)i can see a_little_shop_. 4)mum_ is sad. 5)dad_ is fine. 6)polly_ can see a cat. надо .