In Saving Private Ryan there are scenes where the soldiers are underwater and bullets are shown going into the water with bubbles trailing behind them.
In films with submarines, the propellers often have bubbles coming out.
Where are these bubbles, or the air inside them, coming from?
In: 5
For one, films are not necessarily accurate. With a bullet being shot into the water though I do have an explanation. A fast moving object pushes air out of the way and leaves a low pressure zone behind it. Air wants to move to these low pressure zones. When it is shot into water you can actually see this low pressure zone of air behind the bullet before it fills back up with water.
With a propeller that is already submerged I only have an educated guess. There are air bubbles in water. The propeller pushes the water out of the way and since air moves quicker than water, the bubbles of air fill that low pressure zone before water can.
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