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submitted 6 days ago by fossilesque@mander.xyz to c/science_memes@mander.xyz

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[-] ultratiem@lemmy.ca 18 points 5 days ago

My fav was if you could shoot someone in water. Turns out that just 3 ft. of water was enough to stop a 50 cal! So as great of a film as Saving Private Ryan was, the opening scene where bullets wiz thru the sea killing soldiers was pure fiction.

[-] Jarix@lemmy.world 5 points 5 days ago

Bigger/faster the bullet the easier it was for water to stop. The small rounds from handguns worked best for shooting into water.

It makes sense once they do the maths but it was a great episode

[-] FuglyDuck@lemmy.world 3 points 5 days ago

It isn’t that the water is stoping the bullet- rather that water’s surface tension creates a shockwave that shatters the bullet, and this distributes the mass over more fragments.

Lower power cartridges are able to survive that shockwave, or it fragments into fewer slugs which keeps its energy concentrated.

Either way, I wouldn’t want to be near the high powered cartridge hitting the water. You’re going to feel that shockwave.

[-] Jarix@lemmy.world 2 points 5 days ago

It is the water breaking it. The water doesnt compress so the water doesnt absorb enough of the kinetic energy fast enough so the bullet fractures. As i understand it anyway. The 50cal is travelling a lot faster so a lot more force is applied on the bigger rounds.

Later on they did a dynamite fishing one and we learned being in water when a large enough shockwave hits is VERY bad for internal organs of squishy creatures in it

[-] FuglyDuck@lemmy.world 2 points 5 days ago

It’s the surface tension that causes the shockwave, soapy water wouldn’t have the same effect.

And yes, dynamite explosives are rather more dangerous under water. Which is how torpedos work to break ships without much regard for armor.

[-] Jarix@lemmy.world 1 points 5 days ago

Right so its the water that causes it to break because of the surface tension of the water.

Sounds like you are arguing against my phrasing while agreeing with what i understand. Im confused why we seem to be in a disagreement.

Maybe you can school my dumb ass though, can you eli5 what would need to happen for you to say it was the water that does the work on stopping bullets?

[-] FuglyDuck@lemmy.world 1 points 5 days ago

It’s the interaction between the air and water that does it.

If, hypothetically, you were to move something through the water at that speed, it wouldn’t shatter or just be stopped. There is significantly more drag, so it would come to rest sooner than in air but it wouldn’t just stop.

For example, many small boats have very high rpm propellers that survive just fine- until they start cavitating.

The reason a .50 cal or .308 shatter is the shock of hitting the surface tension, and it’s the shattering that allows the fragments to be slowed down so quickly.

It’s also the reason they were surprised- they forgot to include surface tension in their initial model.

[-] ultratiem@lemmy.ca 1 points 5 days ago

Dynamite in water is the same basic principle used for sea mines. History has taught us those actually work. With the bullet, it’s more about surface tension which makes sense as falling from a high enough cliff onto water if you don’t land right is nearly the same as falling onto concrete.

Cool stuff regardless and I always found their testing to be quite spot on, scientifically.

[-] ChickenLadyLovesLife@lemmy.world 3 points 5 days ago

Bigger/faster the bullet the easier it was for water to stop.

For bullets that's probably true because of their light weight, but heavy shells from the big naval guns of battleships (12" to 18" caliber) actually carried a long way through water and sometimes hit and damaged target ships below the waterline. The Japanese in particular actually designed some of their shells to maximize their underwater performance.

[-] Jarix@lemmy.world 1 points 5 days ago

I wonder relatively what speed those shells would have to hit the water yo behave like bullets and shatter... You wanna revive myth busters and we can find out? Maybe in honor of Grant on his birthday or something would be cool.

We just need a lot of money, some military connections and a way to put the team back together for it

[-] ChickenLadyLovesLife@lemmy.world 1 points 5 days ago

Well, typical muzzle velocities for these shells were in the neighborhood of 2500 feet per second, and although they slowed down some out to typical combat ranges they were still going pretty damn fast when they hit. I don't think the Mythbusters ever had the kind of budget you'd need to test this one out.

[-] zeekaran@sopuli.xyz 1 points 4 days ago

True, but smaller arms go further so scenes line the early betrayal in Italian Job were life threatening.

All supersonic bullets (up to .50-caliber) disintegrated in less than 3 feet (90 cm) of water, but slower velocity bullets, like pistol rounds, need up to 8 feet (2.4 m) of water to slow to non-lethal speeds. Shotgun slugs require even more depth (the exact depth couldn’t be determined because their one test broke the rig). However, as most water-bound shots are fired from an angle, less actual depth is needed to create the necessary separation.