The rockets take astronauts and man-made satellites into space. The satellites are used for communication, weather monitoring and research. But how do satellites stay up without falling down?
There are two opposite forces (力量) acting on the satellite. One of them is the force of gravitation (地心引力), which tries to pull the satellite towards the earth. The other force is created by the rotation (旋转) of the satellite around the earth. This force tries to take the satellite away from the earth. With these two forces, the satellite goes round and round. The gravitational pull of the earth (the force which pulls everything towards the ground) is like a rope which keeps the satellite from flying away.
Everything that goes up has to come down. It is only a matter of time before a satellite comes back to the earth. As time goes by, the satellite loses its speed, which makes the gravitational pull stronger than the force pulling it away. This makes the satellite crash (坠落) down to the earth.
1.Which of the following uses of satellites is NOT mentioned?
A.communication
B.monitoring the weather condition
C.doing some research
D.taking pictures
2.The force that pulls the satellite towards the earth is created by ________.
A.the earth
B.the satellite itself
C.the rotation of the satellite
D.the rope
3.Why can’t the satellites fly away?
A.Because of the force from the earth.
B.Because the satellite is too big.
C.Because of the force created by the rotation of the satellite around the earth.
D.Because people on earth have made ropes to tie the satellites tightly.
4.The satellite will finally crashes down to the earth ________.
A.when it flies faster
B.when its speed slows down
C.when people cut the rope
D.when there is no electricity in it
5.Which of the following is TRUE according to the passage?
A.There are four forces acting on the satellite.
B.The force of gravitation makes the satellite go round and round.
C.As time goes by, the satellite will finally fall down.
D.The satellite will stay in space forever.
Scientists are very interested in the universe and they always want to know more about it.Years ago they knew many things about the _______. They knew how big it was and _______ it was from the earth. _______ they still wanted to know more. They thought the _______ way was to send _______ to the moon. The moon is about 384,000 kilometres away from the earth. A plane cannot fly to the moon because the _______ reaches only 240 kilometres away from the earth. But _______ can fly even when there is no air. That is rocket.
How can a rocket fly? If you want to know, get a balloon and then blow it up until it is quite big. Do not tie up(系紧)the neck of the balloon, but let it go! The balloon will fly off through the air very quickly. The air inside the balloon tries to get out. It rushes out _______ the neck of the balloon and this pushes the balloon through the air. It does not need wings like a plane.
There is gas(气体) in the rocket. So it can fly out into _______. Rockets with men in them have been to the moon. Several rockets have already flown to ________ planet much farther away than the moon. One day, rockets may be able to go to any place in space.
1.A.star B.moon C.sun D.planet
2.
A.how much B.how long
C.how many D.how far
3.
A.So B.And
C.But D.Or
4.
A.worst B.best
C.secret D.correct
5.
A.teachers B.men
C.animals D.computers
6.
A.air B.light
C.Jupiter D.Mars
7.
A.anything B.nothing
C.something D.none
8.
A.by B.on
C.from D.through
9.
A.space B.air
C.cloud D.station
10.
A.the others B.another
C.the other D.others
—I'm afraid I have no time tomorrow.Shall we go to the seaside another day?
—________ Let's make it next week.
A.I'm sorry. B.Of course not.
C.No problem. D.Why?
—When will Mr. Green ________ Beijing?
—In a week.
A. reach B. get
C. arrive D. come
The ice and snow in Harbin is beautiful, so every winter tourists come here.
A.two million of B.millions of C.million of
—Hi, Lily! Why don't you go swimming with them? —Because I ________ my homework yet.
A. didn't finish B. won't finish C. haven't finished D. don't finish
