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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.
Link Posted: 8/17/2005 2:40:24 AM EDT
Link Posted: 8/17/2005 3:02:49 AM EDT
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.
Link Posted: 8/17/2005 3:14:22 AM EDT
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.
Link Posted: 8/17/2005 3:21:25 AM EDT
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
Link Posted: 8/17/2005 3:24:19 AM EDT

Originally Posted By WWoodworth:
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



You made my brain hurt, cant we dumb it down by saying "bullet just bounce off and fall down"
Link Posted: 8/17/2005 9:01:39 AM EDT
[Last Edit: 8/17/2005 9:03:05 AM EDT by keving67]

Originally Posted By WWoodworth:
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



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.
Link Posted: 8/17/2005 9:10:00 AM EDT
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.
Link Posted: 8/17/2005 9:11:46 AM EDT
This reminds me of the fly in the car question.
Link Posted: 8/17/2005 9:13:24 AM EDT
[Last Edit: 8/17/2005 9:13:49 AM EDT by Greenhorn]
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.
Link Posted: 8/17/2005 9:16:14 AM EDT
Damn that would be cool to see, kind of matrix-ish
Link Posted: 8/17/2005 9:22:13 AM EDT
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.
Link Posted: 8/17/2005 9:22:50 AM EDT
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

Link Posted: 8/17/2005 9:26:21 AM EDT

Originally Posted By Greenhorn:
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. . .



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

Link Posted: 8/17/2005 9:28:02 AM EDT
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.
Link Posted: 8/17/2005 9:28:54 AM EDT
Teenagers...they think they know everything...
Link Posted: 8/17/2005 9:30:12 AM EDT
if it's a 9mm it won't make a difference
Link Posted: 8/17/2005 9:33:59 AM EDT
[Last Edit: 8/17/2005 9:43:59 AM EDT by Greenhorn]

Originally Posted By danco:

Originally Posted By Greenhorn:
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. . .



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




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.
Link Posted: 8/17/2005 9:37:36 AM EDT
Link Posted: 8/17/2005 9:39:15 AM EDT

Originally Posted By DDiggler:
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.



Have you been spying on me?


Link Posted: 8/17/2005 9:39:49 AM EDT

Originally Posted By ColonelKlink:

Originally Posted By NoVaGator:
if it's a 9mm it won't make a difference



dude quit punching me.



here comes a full power body shot.........
Link Posted: 8/17/2005 9:41:58 AM EDT
[Last Edit: 8/17/2005 9:42:43 AM EDT by AssaultRifler]

Originally Posted By Greenhorn:
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.



OK, what if you're going say 1/2 the speed of light and turn on your headlights? Will light then travel 1.5 times the speed of light from the headlight?
Never mind, someone just asked it

Link Posted: 8/17/2005 9:42:32 AM EDT
[Last Edit: 8/17/2005 9:42:50 AM EDT by Greenhorn]

Originally Posted By AssaultRifler:
OK, what if you're going say 1/2 the speed of light and turn on your headlights? Will light then travel 1.5 times the speed of light from the headlight?



See my last post. Short answer, no, if Einstein is correct.
Link Posted: 8/17/2005 9:45:00 AM EDT
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.
Link Posted: 8/17/2005 9:45:04 AM EDT

Originally Posted By NoVaGator:
if it's a 9mm it won't make a difference



Its like getting punched.
Link Posted: 8/17/2005 9:47:39 AM EDT
Link Posted: 8/17/2005 9:49:50 AM EDT
[Last Edit: 8/17/2005 10:26:59 AM EDT by Merrell]
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"

Link Posted: 8/17/2005 10:22:46 AM EDT

Originally Posted By ColonelKlink:
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%.



No thing can go the speed of light but NOTHING can.
Now that bakes the noodle
Link Posted: 8/17/2005 10:25:29 AM EDT

Originally Posted By NoVaGator:
if it's a 9mm it won't make a difference



unless you're still traveling at 3001fps and the 9mm is something around 1300fps
Link Posted: 8/17/2005 10:38:03 AM EDT
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
Link Posted: 8/17/2005 10:41:11 AM EDT
[Last Edit: 8/17/2005 10:42:23 AM EDT by danco]

Originally Posted By Greenhorn:
See my last post. Short answer, no, if Einstein is correct.



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
Link Posted: 8/17/2005 11:04:57 AM EDT

Originally Posted By danco:

Originally Posted By Greenhorn:
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. . .



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




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.
Link Posted: 8/17/2005 11:11:50 AM EDT

Originally Posted By WildBoar:

Originally Posted By NoVaGator:
if it's a 9mm it won't make a difference



Its like getting punched.



normal punch...or a squat dog punch?
Link Posted: 8/17/2005 11:22:47 AM EDT
Didn't anyone see 'Rat Race'? The bullet slowly caught up to jet powered racer that was trying to break the sound barrier! Geez!
Link Posted: 8/17/2005 2:23:14 PM EDT


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
Link Posted: 8/17/2005 2:25:02 PM EDT

Originally Posted By danco:

Originally Posted By Greenhorn:
See my last post. Short answer, no, if Einstein is correct.



Actually, Einstein has already been proven correctto the limits of our current ability to test. Relativistic effects have to be taken into account with the GPS satellites, since their clocks tend to run fast...

—Dan



Slight correction...
Link Posted: 8/17/2005 2:25:43 PM EDT

p.s.--There is NO SUCH THING as a stupid physics question.
Link Posted: 8/17/2005 2:50:25 PM EDT

Originally Posted By KS_Physicist:
p.s.--There is NO SUCH THING as a stupid physics question.



No such thing as a short answer either.
Link Posted: 8/17/2005 3:42:22 PM EDT

Originally Posted By keving67:

Originally Posted By WWoodworth:
Incorrect Formula Posted


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




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

Link Posted: 8/17/2005 3:46:20 PM EDT
[Last Edit: 8/17/2005 3:46:54 PM EDT by danco]

Originally Posted By KS_Physicist:

Actually, Einstein has already been proven correctto the limits of our current ability to test. Relativistic effects have to be taken into account with the GPS satellites, since their clocks tend to run fast...


Slight correction...



Ok, I'll buy that!

—Dan
Link Posted: 8/17/2005 3:47:47 PM EDT

Originally Posted By keving67:

Originally Posted By ColonelKlink:
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%.



No thing can go the speed of light but NOTHING can.
Now that bakes the noodle




Light is not nothing.

ColonelKlink - took me a long time to first realize that, then accept it.
Link Posted: 8/17/2005 4:00:46 PM EDT

Originally Posted By keving67:

Originally Posted By ColonelKlink:
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%.



No thing can go the speed of light but NOTHING can.
Now that bakes the noodle



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


Link Posted: 8/17/2005 4:49:04 PM EDT
My cat's breath smells like cat food . . .
Link Posted: 8/17/2005 4:55:33 PM EDT

Originally Posted By glock223:
My cat's breath smells like cat food . . .



By far the funniest Simpson's character
Link Posted: 8/17/2005 4:56:57 PM EDT

Originally Posted By WWoodworth:

Originally Posted By keving67:

Originally Posted By ColonelKlink:
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%.



No thing can go the speed of light but NOTHING can.
Now that bakes the noodle



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





They have actually made light travel faster than, well, light. It was a laser beam actually.
Link Posted: 8/17/2005 5:04:12 PM EDT

Originally Posted By keving67:
They have actually made light travel faster than, well, light. It was a laser beam actually.



I remember reading about that a while back. Whatever happened with that?
Link Posted: 8/17/2005 5:08:23 PM EDT

Originally Posted By keving67:

Originally Posted By ColonelKlink:
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%.



No thing can go the speed of light but NOTHING can.
Now that bakes the noodle



Actually, there are quite a number of subatomic particles that move faster than light. At this point we go to quantum mathmatics.
Link Posted: 8/17/2005 5:12:45 PM EDT
This problem is best solved using the conservation of momentum, not conservation of energy!
Link Posted: 8/17/2005 5:30:30 PM EDT

Originally Posted By keving67:

Originally Posted By WWoodworth:

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





They have actually made light travel faster than, well, light. It was a laser beam actually.



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
Link Posted: 8/17/2005 6:33:07 PM EDT
[Last Edit: 8/17/2005 6:40:56 PM EDT by red65]
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


Link Posted: 8/17/2005 10:05:42 PM EDT
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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