Bullets don’t just bounce off Superman, they don’t even slow him down. Real-life police and soldiers can’t say the same, even when they’re wearing a bulletproof jacket of Kevlar or something similar. Although bullets don’t penetrate–the bulletproof material spreads their force–the force is still tranmsitted to the tissue underneath the bulletproof shell, causing severe bruising or even organ damage.
Now engineers from the Centre for Advanced Materials Technology at the University of Sydney have found a way to use carbon nanotubes to not only stop bullets penetrating material but actually rebound their force, so bullets can be repelled with "minimum or no damage to the wearer of a bullet proof vest.” (Via Science Blog.)
If they can just nail the X-ray vision, super-strength and flying stuff, they can break out the red-and-blue tights. (Image from Wikimedia Commons.)
[tags]nanotechnology, security, military, police[/tags]
I suggest you file this under fiction. It has been known since the 17th Century (Newton) that: “For every action, there is a equal and opposite reaction.” If the bullet “bounces” off the vest with equal velocity, that will DOUBLE the momentum transferred to the tissues behind the vest!
I don’t follow. The equal and opposite reaction is precisely what makes the bullet rebound: it’s just that the energy absorbed by the material at the moment of impact is released by the material springing back into shape, instead of being transferred to whatever is on the other side of it. If I’m wearing a suit made of, say, wood, and you hit me in the side with a baseball bat, a lot of that force is going to be transferred through the non-springy wood to my ribs, even though some of it will be absorbed and spread out trough the wood. If I’m wearing a suit made of springy rubber, your bat will bounce off and far less of that force will be transferred. You seem to be saying that the force of the impact would be doubled by the springy suit.
That is precisely what I am saying. Newton’s second law is usually stated F=m*a. Its meaning is clearer as F= delta p. The force applied to a body is equal to the change in momentum of the object applying the force. If a bullet is stopped by the body, it transfers a momentum equal to the mass of the bullet times its velocity on impact. If the bullet arrives and springs off the surface of the body at a velocity equal to its incoming velocity but opposite in sign, the change in bullet momentum is TWICE that of a bullet coming to rest. All of that momentum is transferred (by the spring) to the body. There is nowhere for the momentum to go except into the body.
The dynamics of “spreading out” the impact momentum is limited by the speed of sound in the “spring” material, and the transfer of momentum to the body is controlled by the deformation of the bullet, which occurs at the speed of sound in the metal. The momentum really cannot, for physics reasons, be spread very far laterally in the time it takes the bullet to impact.
For very fundamental physics reasons, this proposal is fantasy trying to ride the nanotech funding bubble.
Interesting. Thanks for the explanation!
You are most welcome! I spent about a decade designing and building “electrothermal guns.” I continue to be amazed how often the basics of science are overlooked when an appealing story line has been constructed.
I agree totally docduke. Do bullet proof vests protect from taser stun guns