问题 填空题

潜水艇是靠______实现的上浮和下沉.

答案

在水中,潜水艇受到水的浮力和重力的作用,

∵Fvg,潜水艇的体积不变,排开水的体积不变,

∴潜水艇受到水的浮力不变;

把压缩空气压入潜水艇的压力舱,将海水排出,潜水艇自重G减小,当F>G时,潜水艇上浮;

打开压力舱的阀门,让海水进入压力舱内,潜水艇自重G增大,当F<G时,潜水艇下沉;

当F=G时,潜水艇悬浮,可以停留在任何深度;

由此可见,潜水艇能够上浮和下沉是通过改变自身重力来实现的.

故答案为:改变自身重力.

完形填空

Mike always loves ships. When he was older, he said, “I’m going to be a soldier.” But his eyes were not very ___1_____, and he did not get in.

  Then he said,“I’m going to   2  a small boat and I’m going around the world.”But boats were very expensive, and Mike did not have enough   3   .

  Last summer Mike found a swimming   4    near his house. The lessons did not cost very   5   , and Mike began going to the school at every end of the week and having   6  . Now he is a good swimmer.

  Last week a little boy said to him,“You’re a very good swimmer. How do   7  learn to swim so well?”

  “I’m not good at all,”Mike said and he smiled.“  8  I’m in the water, I say to myself, There are   9  fishes behind me! Then I’m very afraid, and I    10   quickly.”

(       ) 1. A. big        B. beautiful   C. good         D. strong

(       ) 2. A. buy        B. make     C. borrow        D. draw

(       ) 3. A. food       B. work      C. time          D. money

(       ) 4. A. park       B. school     C. farm          D. factory

(       ) 5. A. much      B. little       C. many         D. any

(       ) 6. A. meals      B. lessons      C. talks         D. games

(       ) 7. A. I         B. they        C. we         D. you

(       ) 8. A. If         B. When       C. Though      D. Where

(       ) 9. A. interesting  B. nice       C. dangerous     D. different

(       ) 10. A. run       B. jump      C. swim         D. fly

判断题