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Q & A: Super Bullets!

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Most recent answer: 10/22/2007
Q:
Can a bullet go faster in water than in air--- I have been told that & I don’t think it’s logical
- jeannette
RNMH
A:
You are thinking logically when you say that bullets should not be able to travel faster in water than in air. In most cases any projectile entering the water will be slowed down by drag. This we know from jumping into a swimming pool. However there is a special case known as supercavitation which involves powerful torpedoes that are able to travel at super speeds beneath the water surface with minimal drag. The key to supercavitation is creating an object (bullet, torpedo) with a nose specially shaped and firing at a very high velocity so that it creates a low pressure zone around the entire object. At this high velocity the water will flow off the nose at angles preventing it from wrapping around the projectile and creating drag. The low pressure bubble that is created around the object will allow the object to reside in a vapor cavity. Drag is proportional to the density of the surrounding fluid therefore because this proportion is smaller due to the low pressure and vapor cavity, there will be reduced drag and the object will be able to continue at super fast speeds.

(published on 10/22/2007)

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