题干

如图是一种水翼船船体下安装的水翼,在高速行驶时,水面下的水翼会将船体抬高从而减小水对船的阻力.请你判断水翼的形状应是图中甲、乙的哪一个?并解释当船高速航行时,船被抬高的原因.

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甲图.原因:在流体中流速越大的位置,压强越小.当船在水中高速航行时,水翼上表面凸起,它与船体间的水流速度大,压强小;水翼下表面的水流速度小,压强大,因此在水翼的上下表面存在向上的压力(压强)差,所以船体被抬高了.

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    “Mum, what does it mean when someone tells you that they have a skeleton(骨骼) in the closet?” Jessica asked. “A skeleton in the closet?” her mother paused thoughtfully. “Well, it's something that you would rather not have anyone else know about. For example, if in the past, someone in Dad's family had been arrested for stealing a horse, it would be ‘a skeleton in his family's closet'. He really wouldn't want any neighbor to know about it.”

    “Why pick on my family?” Jessica's father said with anger. “Your family history isn't so good. You know. Wasn't your great-great-grandfather a prisoner who was sent to Australia for his crimes?” “Yes, but people these days say that you are not a real Australian unless your ancestors arrived as prisoners.” “Gosh, sorry I asked, I think I understand now,” Jessica cut in before things grew worse.

    After dinner, the house was very quiet. Jessica's parents were still quite angry with each other. Her mother was ironing clothes and every now and then she glared at her husband, who hid behind his newspaper pretending to read. When she finished, she gathered the freshly pressed clothes in her arms and walked to Jessica's closet. Just as she opened the door and reached in to hang a skirt, a bony arm stuck out from the dark depths and a bundle of white bones fell to the floor. Jessica's mother sank into a faint(晕倒), waking only when Jessica put a cold, wet cloth on her forehead. She looked up to see the worried faces of her husband and daughter.

    “What happened?Where am I?” she asked. “You just destroyed the school's skeleton, Mum,” explained Jessica. “I brought it home to help me with my health project, I meant to tell you, but it seemed that as soon as I mentioned skeletons and closets, it caused a problem between you and Dad.” Jessica looked in amazement as her parents began to laugh madly. “They're both crazy,” she thought.