The Science Of Under Water Gun Shooting: Can Jumping Into Water Bodies Protects Us From Bullets?

Have you ever wondered why people always have to dive into water bodies when they come under sudden gun attack and there is a water body nearby, be it pool, river, sea, etc? While, perhaps, you might not have witnessed this in real life but I want to believe you might have watched some movies where a scene such as this actually played out. One of such scenes which can serve as a great reminder is the opening scene of the movie — Saving Private Ryan — during which the Allied Forces had to jump into water from the sides of the boats to avoid being hit by bullets when they come under heavy gun attack from the bunkers on the Omaha Beach. To get the real gist of what I am talking about, let's take a moment and watch this YouTube video clip of that particular scene: Just scroll to 2.22minutes in the second image.

_{[Source: Pixabay. CC0 licensed]}

The above is just an instance. There are countless of such scenes in movies and even in real life situations where people deliberately jumped into water bodies. Even my dad told me about the great battle of Onitsha when federal troops made several unsuccessful attempts to cross River Niger by boats during Nigeria civil war. My dad, being one of the errand boys for Biafran troops since he was not yet mature for military enlistment, recounted how Nigerian troops led by then Lt. Col. Adeyinka would always jumped in to River Niger when their boats were being rained by bullets.

That what baffled him most was that despite the intensity of the bullets, only a handful of Nigerian troops would later float on the river and sometimes washed ashore, afterwards; meaning that the rest went scot-free. Adding to this confusion, according to my father, was the fact that he had also witnessed scenes where some hurriedly conscripted Biafran soldiers with no war experiences became scared on realizing what war front situations were like, and made for water bodies to escape fighting. A number of such renegades were shot at and killed by their commanders even when they had succeeded in jumping into water.

So, it's kind of complicated, confusing and mysterious. Is it that sometimes being underwater saves you and sometimes it doesn't? What could have been responsible for this? My dad have lived with this question for a damn long time, and with no logical explanations forthcoming, he had to attribute it to superstition and diabolism until the issue came up lately when he wanted to feed me with his superstitious lies😂, but I refused to agree with him and had to dig up scientific responses to such phenomenon. To help advance knowledge and clear up the uncertainty around this underwater myth once and for all, I have decided to share my findings with the community.

Demystifying the underwater bullet myth: speed vs. drag interaction

The underwater behavior of a bullet is dependent on a number of factors the most important of which is know as drag. As a matter of fact, every medium poses some resistance whenever an object moves through it, and this resistance increases with the speed of the object and also varies between different media. For example, water offers stronger resistance against movement of an object than air.

_{[Source: Pixabay. CC0 licensed]}

When we walk or run around, we are being hindered by air molecules that we have to clear out of the way in order to keep running or walking. However, we are so used to resistance posed by air molecules that we hardly notice it. But that doesn't mean it isn't there. One way to notice this resistance is to extend your arm out through the side window of a vehicle at high speed. Your arm would definitely be swayed about by air molecules trying to oppose your movement. This resistance which tries to oppose the movement of an object is called drag.

We quickly get tired when we swim through water than when we walk through air because water offers more drag against our movement than air molecules. The same is true for a bullet when it enters a water body. A bullet moves through the air easily because of the insignificant drag force of air molecules against its forwards thrust. But as soon as it enters a water body, things change very drastically. It has to work extra hard against the much stronger drag force opposing it. Unfortunately, however, most bullets do not go beyond a few feets in a water body before they are completely neutralized and brought down.

Banking on this simple physics, Andreas Wahl was reported to have demonstrated this using himself as the experimental specimen. He simply walked into a pool, stood in front of a loaded cartridge under the water and fired it at himself. Below is the slow motion view of the demonstration showing how the bullet struggles as it moves through water. (Just a minute clip).

Speaking after the successful demonstration, he said:

"It's harder to create movement in water than in air, because water molecules are closer together than air molecules." It's all about resistance. A bullet flying through the air faces very little resistance and can travel far at a high speed. In the water, it faces all sorts of drag that impedes its progress" || _Source

As we can see, drag is the major factor opposing the movement of a bullet under water. However, the amount of drag water molecules would exert on (say) two different objects moving through it is not the same. It actually depends on a number of factors including drag coefficient of the fluid (water) and its density, the type of bullet, the speed with which the bullet was fired and the time it has spent in water. All these factors work together to determine the amount of drag to be exerted against the movement of a particular object as expressed by the Lord Rayleigh's (drag) equation below:

_{[Source: flickr commons. Author: Richard Masoner. CC BY-SA 2.0 licensed]}

From the above equation, F is the drag force, rho "p" is density of the medium, V is the object velocity, A, reference area while C is the drag coefficient.

As we can see based on the drag equation above, drag force increases with the square of velocity and with the density of the medium (fluid) "p". The value of "p" for water has been found to be about 1000 times more than its value for air. This is to say the drag force F that would act against the bullet will increase by a factor of 1000 as soon as the bullet enters the water. Once this condition is met, the velocity of the bullet will quickly decrease for each millimeter covered.

Guys at the popular Discovery Channel show, Mythbusters having tested bullet resistance ability of water against different bullets from such guns as 9mm pistol, short gun, supersonic M1 Garand semi-automatic riffle and .50 cal rifle; concluded that one can protect oneself against bullets (shot directly overhead from many guns) by diving into a water body and keeping to a distance of at least 8 feet underwater. However, in practice, bullets are rarely fired from a position that's directly above water; they are usually fired at an angle and this makes it even more difficult for bullets to move through. For instance, if fired at 30 Degree angle, one would only have to be 3 feet underwater to be safe from the bullet's harm way.

Applying the preceding discourse to my father's civil war experiences, it is obvious that those soldiers who were killed despite having dived into a water body stayed too closer to the surface than the 8feet, 3feet recommended thresholds. While those who weren't harmed must have stayed at distances that correspond with the given standards. Thanks for reading.

References

• _{How much speed does a bullet lose when fired into water?}
• _{Daredevil physicist braves under waster science}
• _{Can being underwater protects you from bullets?}
• _{Drag equation}

Truly yours,
@sciencetech
STEM contributor