普通高中课程标准实验教科书英语必修高一下必修3 Unit 4 Astronomy: the science of the stars-Using Language
A VISIT TO THE MOON
Last month I was lucky enough to have a chance to make a trip into space with my friend Li Yanping, an astronomer. We visited the moon in our spaceship!
Before we left, Li Yanping explained to me that the force of gravity would change three times on our journey and that the first change would be the most powerful. Then we were off. As the rocket rose into the air, we were pushed back into our seats because we were trying to escape the pull of the earth's gravity. It was so hard that we could not say anything to each other. Gradually the weight lessened and I was able to talk to him. "Why is the spaceship not falling back to the earth? On the earth if I fall from a tree I will fall to the ground." I asked. "We are too far from the earth now to feel its pull," he explained, "so we feel as if there is no gravity at all. When we get closer to the moon, we shall feel its gravity pulling us, but it will not be as strong a pull as the earth's." I cheered up immediately and floated weightlessly around in our spaceship cabin watching the earth become smaller and the moon larger.
When we got there, I wanted to explore immediately. "Come on," I said. "If you are right, my mass will be less than on the earth because the moon is smaller and I will be able to move more freely. I might even grow taller if I stay here long enough. I shall certainly weigh less!" I laughed and climbed down the steps from the spaceship. But when I tried to step forward, I found I was carried twice as far as on the earth and fell over. "Oh dear," I cried, "walking does need a bit of practice now that gravity has changed." After a while I got the hang of it and we began to enjoy ourselves.
Leaving the moon's gravity was not as painful as leaving the earth's. But returning to the earth was very frightening. We watched, amazed as fire broke out on the outside of the spaceship as the earth's gravity increased. Again we were pushed hard into our seats as we came back to land. "That was very exhausting but very exciting too," I said. "Now I know much more about gravity! Do you think we could visit some stars next time?" "Of course," he smiled, "which star would you like to go to?"
