BAND1 TEST4BAND1 TEST4.docVIP

BAND 1 Test 4 Passage 1 The Earth has a force that pulls things toward it. We call this force gravity. This is something we live with all the time, and we take it for granted and hardly ever think about it . But it is a most important factor in rocket operation and must be overcome if we are to get anywhere in space, or off the ground at all. Take the throwing of a ball as an example. We harder the ball is thrown, the faster and higher it will go. What is the secret? Its speed. If we could throw the ball hard enough it would go up and up and up forever and never come down. The speed at which it would have to be thrown to do this is known as escape speed. Of course, we cannot throw a ball hard enough because the speed required for the ball to escape completely from the Earth’s gravity is sever miles per second, or over twenty-five thousand miles per hour . Once a spacecraft has reached escape speed, no further power is needed. A rocket aimed at the Moon , for instance , will “coast”(滑行)the rest of the way because the Earth’s gravity cannot then pull it back , and there is no air resistance in space to slow it down . This “coasting” is known as “free fall” . That does not mean the rocket is falling down towards the Earth but it is traveling freely in space without the aid of power, like a bicycle coasting downhill. Free fall is an important feature of space travel: it would be impossible to carry enough fuel to provide powered flight all the time. What is the most important factor for a rocket to escape form the Earth? A. To travel as fast as it can C. To reduce the air resistance. B. To overcome the Earth’s gravity. D. To carry enough fuel with it . How fast will a rocket go to escape completely from the Earth’s gravity? Seventy miles per second. Seven thousand miles per hour. Twenty-five thousand miles per second. Twenty- five thousand miles per hour. As there is always the Earth’s gravitational pull, people______. A.