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Some of the best moments in World War II movies occur when, during a battle at sea, a periscope pokes up from the water, surveying the ocean terrain.
二戰題材的電影中一些可贊的片段是，海上作戰的時候，一個潛望鏡從水中穿出，用以測量海洋地形。
Cut to a submarine gliding through the depths. Torpedoes away, and the enemy battleship is doomed. How do these amazing vessels rise and sink so quickly to specific depths?
鏡頭切換到潛水艇潛到水下。然后發射魚雷，敵軍戰隊注定會失敗。這些神奇的軍艦是如何實現快速上升下沉到特定的深度?
Although submarines are sophisticated machines, their ability to rise and sink is based on the elementary principle of buoyant force.
盡管潛艇是很復雜的機器，但它們上升下沉所依據的卻是浮力的基本原理。
Say you fill your bathtub with water and put a rubber gym ball on the surface of the water.
將浴缸填滿水然后在水面上放一個橡膠健身球。
It floats because the air-filled ball is less dense than the surrounding water.
它會在水面上漂著因為充氣球的密度小于水的密度。
But poke a hole in the ball and as water displaces the air, the overall density increases until the ball is heavy enough to sink to the bottom.
但在球上戳一個洞，用水代替健身球中的空氣，其整體密度會變大，一直到該球重的足以落到水的底部。
譯文來自可可英語
