问题
问答题
对着两张平行拿着的纸张中间吹气，两张纸张将怎样运动？为什么？
答案
答：两张纸将会向中间靠拢；
因为没有吹气时，纸的中间和外侧的压强相等，纸在重力的作用下自由下垂．当向中间吹气时，中间的空气流动速度增大，压强减小．纸外侧的压强不变，纸受到向内的压强大于向外的压强，受到向内的压力大于向外的压力，纸在压力差的作用下向中间靠拢．
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对着两张平行拿着的纸张中间吹气，两张纸张将怎样运动？为什么？
答：两张纸将会向中间靠拢；
因为没有吹气时，纸的中间和外侧的压强相等，纸在重力的作用下自由下垂．当向中间吹气时，中间的空气流动速度增大，压强减小．纸外侧的压强不变，纸受到向内的压强大于向外的压强，受到向内的压力大于向外的压力，纸在压力差的作用下向中间靠拢．
re. If he came as 39 as this every morning, he would get a lot more 40 done.” John began to get on with his work and by half past nine he had 41 all the postcards he had to write. It was a quarter to ten, and Mary had not arrived 42. He wondered 43 she was ill or if she had taken the day 44. But Mr. Steele came and 45 him if he knew where Mary was. If she were ill, she would 46, he said. It’s not like her. She’s usually 47. John said that he had no 48 where Mary was. But 49 the door opened and there was Mary. She was looking very 50 and tired. She apologized to Mr. Steele and explained that she had been 51 most of the night. She hadn’t 52 to sleep until five in the morning and had overslept. Mr. Steele was very 53 and suggested that she take the day off. She 54 him and said she would stay, but she 55 said a word for the rest of the morning. John, on the other hand, was feeling happy so at one o’clock he suggested to Mary that they go and have lunch together, and she agreed.