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Posted: 8/17/2005 2:28:47 AM EDT
Okay my son brought this up and I dont have a clue. If you were travelling 3000fps directly in front of a bullet travelling 3001 fps would the bullet have any impact energy? I would think it would have a relative speed of 1fps and therefore no energy. He countered that although it would only travel at 1fps relatively it would still carry energy and penetrate. I think I've been outclassed by a 14 year old.
I figured I'd post this really late so less could see it and think I'm a complete dork. 
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Posted: 8/17/2005 2:40:24 AM EDT
[#1]
The bullet would impact at 1 FPS and deliver very, very little additional energy to you.
But when you slow down from 3001 FPS to zero, you'd better do it in a controlled manner! CJ |
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Posted: 8/17/2005 3:02:49 AM EDT
[#2]
Have him think of it this way...
If you're in a car going 55 mph, and your buddy pulls up next to you in another car going 56 mph, and tries to hand you a burrito or something, is it going to transfer the energy of 56 mph to your hand? No. It's all relative. |
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Posted: 8/17/2005 3:14:22 AM EDT
[#3]
It would be the same as if he was standing still and a bullet hit him going 1 fps. Yes, there will will be Kinetic energy (KE = 0.5mv^2) but very small. Basically, for this problem, the KE is one half the mass of the bullet.
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Posted: 8/17/2005 3:21:25 AM EDT
[#4]
Since Force = Mass x Accleration, the rate of deceleration over the impact would be 1 ft/sec per X time. The reason being that the bullet (and you attached to it) would still be moving at 3000 ft/sec. Mass of the bullet would be constant.
Since Power = Mass x Velocity, the power of the bullet would be again a relative measurement. If it is moving at 3001 fps, and you (with considerably more mass) are moving at 3000 fps, it sounds like the bullet has a lot more to worry about than you. Okay, I am dredging up 20+ year old physics concepts, so someone feel free to correct me if I'm incorrect. Woody |
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Posted: 8/17/2005 3:24:19 AM EDT
[#5]
You made my brain hurt, cant we dumb it down by saying "bullet just bounce off and fall down" |
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Posted: 8/17/2005 9:01:39 AM EDT
[#6]
You are assuming a constant rate of decceleration upon impact. Power = Work / Time not mass times velocity. Mass * Velocity is the equation for momentum. If by Power you meant Energy (kinetic in this example) then it is KE = 0.5*m*v^2 You could use the conservation of momentum equation: Mass(bullet)*Velocity(bullet) + Mass(your son)*Velocity(your son) = Mass(combined)*Velocity(combined) But the change is going to be very small. Because the problem assumes that the velocity of the bullet and your son are constant, there will be no acceleration (F=M*A). The bullet will then have no force to penetrate. |
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Posted: 8/17/2005 9:10:00 AM EDT
[#7]
Engineers. Math People. I swear, I deal with this shit every day when I go to school. I can't even play a game of pool without hearing it. More power to you though, if you can wrap your noodle around this kind of thing on a daily basis. I get panicky just thinking about it.
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Posted: 8/17/2005 9:11:46 AM EDT
[#8]
This reminds me of the fly in the car question.
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Posted: 8/17/2005 9:13:24 AM EDT
[#9]
If you are standing in the back of the van facing backwards and the van is going at 65mph, and you throw a baseball out of the van at 65mph, it will land in exactly the same way as if the van were stopped and you dropped the ball out the back. If a person standing on the ground shot a bullet at 3000 fps at you while you passed him at 3001 fps, it would be like the person very gently tossed the bullet at you.
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Posted: 8/17/2005 9:16:14 AM EDT
[#10]
Damn that would be cool to see, kind of matrix-ish
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Posted: 8/17/2005 9:22:13 AM EDT
[#11]
I remember reading once where they did some experiments in WWII where they noticed that nose guns penetrated ground targets better than tail guns.
The reason? Nose guns have the standard velocity plus the airplane speed. Tail guns have the standard velocity minus the airplane speed. |
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Posted: 8/17/2005 9:22:50 AM EDT
[#12]
Momentum
Momentum (p) is the quantity of motion in a body. A heavy body moving at a fast velocity is difficult to stop. A light body at a slow speed, on the other hand can be stopped easily. So momentum has to do with both mass and velocity. p = mv Often physics problems deal with momentum before and after a collision. In such cases the total momentum of the bodies before collision is taken as equal to the total momentum of the bodies after collision. That is to say: momentum is conserved. Formula: P = m x v 
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Posted: 8/17/2005 9:26:21 AM EDT
[#13]
If you were in the back of a van going the speed of light, could you see to shoot the driver, or would all of the light be piled up against the rear wall of the van??? Or, would you get hit with your own bullet as it exited the muzzle and flew backward? Or, since nothing can travel faster than light, and if you are already travelling at light speed and a bullet travelling forward would be going faster than light, would your gun just explode? Or, would the speed of light in your frame of reference remain the same, but time slow down such that you could easily see and shoot the driver, although for an observer in a different reference frame it seemed to take you and infinte amount of time to pull trigger? Stupid Einstein and his Relativity... —Dan |
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Posted: 8/17/2005 9:28:02 AM EDT
[#14]
You didn't mention direction of travel :-)! If going in opposite directions, then you would have quite an inpact! 6001 fps relative bullet velocity would really ruin your day.
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Posted: 8/17/2005 9:28:54 AM EDT
[#15]
Teenagers...they think they know everything...
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Posted: 8/17/2005 9:30:12 AM EDT
[#16]
if it's a 9mm it won't make a difference
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Posted: 8/17/2005 9:33:59 AM EDT
[#17]
According to the theory, you can't travel faster than light. The closer you get to the speed of light, the more your own mass increases, which makes it necessary to add more thrust to accelerate, which adds more mass, etc etc. Eventually, no matter how much thrust you have, you will only ever get infinitely close to the speed of light, but you will not reach it, and you will reach almost infinite mass (yes, I realize that "almost infinite" makes no sense). If you were traveling at almost the speed of light, any light that you made would travel away from you at the speed of light. Now of course logic says that if you are headed toward the Earth at the speed of light, and the light from the flashlight goes away from you at the speed of light, the light must hit the Earth at almost double the speed of light, right? Well, that's not how it works. It will hit the Earth at the speed of light. This descrepancy is accounted for by a bending of time. Strange, huh? People on the Earth, when looking at you coming toward them with a flashlight, would see an extremely blue-shifted point of light in the sky, and you would be moving VERY slowly - in fact, your speed would be perfectly indirectly preportional to how close you were to the speed of light. To them, your time would have slowed down. To you, their time would have sped up. I think I've gotten these facts correct. If I'm wrong on something you can correct me. |
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Posted: 8/17/2005 9:37:36 AM EDT
[#18]
dude quit punching me. |
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Posted: 8/17/2005 9:39:15 AM EDT
[#19]
Have you been spying on me?  |
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Posted: 8/17/2005 9:39:49 AM EDT
[#20]
here comes a full power body shot......... |
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Posted: 8/17/2005 9:41:58 AM EDT
[#21]
Never mind, someone just asked it |
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Posted: 8/17/2005 9:42:32 AM EDT
[#22]
See my last post. Short answer, no, if Einstein is correct. |
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Posted: 8/17/2005 9:45:00 AM EDT
[#23]
At a relative impact velocity of 1 fps, the bullet would have a very small amount of impact energy, but would not penetrate. Studies have found that impact velocities need to be quite a bit higher than this for a projectile to penetrate skin.
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Posted: 8/17/2005 9:45:04 AM EDT
[#24]
Its like getting punched. 
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Posted: 8/17/2005 9:47:39 AM EDT
[#25]
You know what really bakes the noodle is that if you were moving at 95% of the speed of light and a light ray passed you, it would appear to you going 100% the speed of light and not 5%.
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Posted: 8/17/2005 9:49:50 AM EDT
[#26]
If you were travelling 3000fps directly in front of a bullet travelling 3001 fps it was probably fired by a bitter ex-gilfriend, who got dumped by the pool boy she was banging and has now decided to make your life a living hell for her poor choices in life, when ending a relationship, exiting said gf's apartment at at least 3500 fps is recommended, 4500 fps if it is "that time of the month"
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Posted: 8/17/2005 10:22:46 AM EDT
[#27]
No thing can go the speed of light but NOTHING can. Now that bakes the noodle |
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Posted: 8/17/2005 10:25:29 AM EDT
[#28]
unless you're still traveling at 3001fps and the 9mm is something around 1300fps |
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Posted: 8/17/2005 10:38:03 AM EDT
[#29]
A 55gr bullet traveling 1fps would have less energy then airsoft BB at 300fps. However, if you're traveling at 3001 fps with a BC of .00000000000001 you'd catch on fire from the friction.
Shok |
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Posted: 8/17/2005 10:41:11 AM EDT
[#30]
Actually, Einstein has already been proven correct. Relativistic effects have to be taken into account with the GPS satellites, since their clocks tend to run fast... —Dan |
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Posted: 8/17/2005 11:04:57 AM EDT
[#31]
None of the above. No matter how fast you travel, everything would be perfectly normal inside the van. Of course, some interesting things might appear to happen to people not travelling the same speed as you, and they will observe some interesting things happening in the van. |
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Posted: 8/17/2005 11:11:50 AM EDT
[#32]
normal punch...or a squat dog punch? |
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Posted: 8/17/2005 11:22:47 AM EDT
[#33]
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Posted: 8/17/2005 2:23:14 PM EDT
[#34]
It's Newtonian relativity, and you are right. What matters in the impact is the differential velocity between bullet and target. The bullet hits you at 1 fps, and the impact point absorbs the energy difference for the bullet travelling 1 fps. You and the bullet are then presumably a system (you have it in your pocket or whatever) and the system, you plus the bullet, have the kinetic energy of you at 3000 fps and the bullet at 3000 fps. The kinetic energy of the bullet's differential speed, 1fps, is lost as heat or deformation in the impact point. Jim |
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Posted: 8/17/2005 2:25:02 PM EDT
[#35]
Slight correction... |
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Posted: 8/17/2005 2:25:43 PM EDT
[#36]
p.s.--There is NO SUCH THING as a stupid physics question. |
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Posted: 8/17/2005 2:50:25 PM EDT
[#37]
No such thing as a short answer either. |
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Posted: 8/17/2005 3:42:22 PM EDT
[#38]
Oops. Told you, I last took a physics course 20 years ago. M*V is, indeed, the formula for Momentum. I feel stupid now. (runs off to hide) Woody |
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Posted: 8/17/2005 3:46:20 PM EDT
[#39]
Ok, I'll buy that! —Dan |
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Posted: 8/17/2005 3:47:47 PM EDT
[#40]
Light is not nothing.  ColonelKlink - took me a long time to first realize that, then accept it. |
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Posted: 8/17/2005 4:00:46 PM EDT
[#41]
But, what can travel faster than the speed of light? And I'm not talking the Millenium Falcon, or any ship beginning with NCC-1701 Physics trivia for the day.... Woody |
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Posted: 8/17/2005 4:49:04 PM EDT
[#42]
My cat's breath smells like cat food . . .
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Posted: 8/17/2005 4:55:33 PM EDT
[#43]
By far the funniest Simpson's character |
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Posted: 8/17/2005 4:56:57 PM EDT
[#44]
They have actually made light travel faster than, well, light. It was a laser beam actually. |
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Posted: 8/17/2005 5:04:12 PM EDT
[#45]
I remember reading about that a while back. Whatever happened with that? |
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Posted: 8/17/2005 5:08:23 PM EDT
[#46]
Actually, there are quite a number of subatomic particles that move faster than light. At this point we go to quantum mathmatics. |
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Posted: 8/17/2005 5:12:45 PM EDT
[#47]
This problem is best solved using the conservation of momentum, not conservation of energy!
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Posted: 8/17/2005 5:30:30 PM EDT
[#48]
Yep. And it was through some media (I don't remember what it was). Two transmitters, two receivers, one path with a substance between the two, and the straight path light got there last. I thought that was rather interesting. Woody |
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Posted: 8/17/2005 6:33:07 PM EDT
[#49]
Ok, you guys don't know jack sh-t about kinematics.
The bullet would hit you going 1 fps. Your son is sort of correct, because the bullet would slow down from 3001 fps to 3000 fps that's not the same as it slowing down from 1 fps to 0 fps. The bullet has a lot of kinetic energy at 3001 fps but it's only going to dump off a little bit of it when your chest slows it down to 3000 fps. The amount of energy available to rupture your body is = 1/2 x mass of bullet x 3001 x 3001 - 1/2x mass of bullet x 3000 x 3000 don't forget to divide the lbs of bullet weight by 32.174 ft/sec/sec to convert the lbs weight to mass. the mass unit is called "slugs". no kidding. it's going to be a very small number, like 2 ft lbs delivered into your skin side note - weight = mass x gravity newton = kilograms x 9.81 meters/sec/sec pounds = slugs x 32.174 ft /sec/sec |
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Posted: 8/17/2005 10:05:42 PM EDT
[#50]
Red, since the bullet and the body are then both travelling at 3000fps when the bullet decelerates would it be able to be moved off it's flight path by the hand or would the forward force still be a factor even though you move at the same speed?
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