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找到一个一般认为
Unfortunately, there is an extremely prevalent misconception about bullet impacts in this reddit, and I see it surface again and again in discussions pertaining to armor and helmets.
In every discussion about helmets, I see people saying “Even if the helmet stops the bullet, you would die from the shock, your neck would snap etc. Etc.” This is just plainly wrong, and people need to stop spreading this nonsense.
So once and for all; Bullets do not kill because of the force they exert on your body. Bullets kill because a force is concentrated into a very small area (the bullet), causing it to penetrate your body and do a lot of damage. So bullets do not kill because of a large force, but rather because of a very high “Force density”. This very well exemplified by considering the firing of a rifle. Due to Newton’s third law, the same force that accelerates the bullet is also exerted on the rifle. However, since the bullets mass is roughly 1000 times smaller than the rifle’s, the acceleration is 1000 times smaller. This is why you don’t die from the recoil when firing a rifle.
So how does this relate to armor and helmets? Lets assume a bullet impacts on an armor plate or a helmet, and it is completely stopped. That is, no penetration, and no sizable backside deformation. In this case, the bullet transfers its momentum to the armor plate/helmet, exerting the same force as was used to fire it. However, the mass of the helmet/armor plate is comparable to a rifle, I.e. 1000 times larger than the bullet. The bullet impact on armor plate/helmet is thus comparable to the recoil felt in the rifle that fired the bullet.
Imagine putting on a helmet, placing the buttstock of your rifle against your helmet and squeezing the trigger. Do you think you would become brain dead, or that your neck would snap? No? Then stop saying this would happen when a bullet impacts a helmet!
“Then why is so difficult to make helmets withstand rifle calibers?” It’s not difficult to make a helmet capable of withstanding rifle calibers. It’s difficult to make such a helmet while keeping it light enough to be practical. A helmet needs to cover most of your head, while at the same time only weighing a couple Kgs at most.
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