​​​​There's no air underwater, yet submarine and ship propellers leave behind a trail of bubbles. Why?


This is a process called cavitation. When propeller rotates, there exists a suction pressure on one side of its blade. When this suction pressure falls below the vapors pressure of water, the water bubbles form due to boiling of water at very low pressure and normal temperature. Yes, water can boil at room temperature if the pressure is reduced to sub-atmospheric levels.

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