Since t__________ of millions of years the moon has been going round the earth. A_____ this time. The moon was the only satellite (satellite) of the e_______. Today the earth has many other satellites. All of them are made by man. These man -made satellites are m_______ smaller than the moon. Some of them will still go round the earth thousands of years.
Man-made satellites don f_____ because they are going too fast to do s_____. The pull of the earth k______ them from doing this. As a result, they travel in an orbit (orbit) round the earth.
If a man-made satellite travels about a certain height, it can keep g_________ round the atmosphere (air), and there is n________ to slow it down. If it travels lower than that, it will be slowed down so m_____ that it will fall to the earth.