十万个为什么·科学启蒙30篇（2）
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How Do Submarines Control Their Depth Underwater?
潜艇如何控制水下的深度？
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Submarines control depth using ballast tanks that fill with water to sink or air to rise.
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When valves open, seawater rushes in and increases the sub’s overall density beyond seawater.
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To ascend, compressed air pushes water out of the tanks, making the vessel lighter than water.
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Hydroplanes—small wing-like fins—tilt upward or downward to steer while moving forward.
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Even tiny imbalances in weight distribution require constant fine-tuning by onboard computers.
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Nuclear-powered subs can stay submerged for months because they don’t need surface air for engines.
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Modern subs also use sonar to map nearby terrain and avoid underwater mountains or cliffs.
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Emergency blow systems release high-pressure air instantly if the crew must surface fast.
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Saltwater density changes with temperature and salinity, so depth sensors adjust continuously.
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Every dive begins with careful calculations to ensure safe pressure limits for the hull.