bullet bullistics.

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bullet bullistics.
« on: December 21, 2007, 02:21:55 PM »
when you fire a bullet parallel to the ground it travels very fast, it slowly starts to come to earth due to gravity (RE) (among other things.)

but in FE, with the earth travelling up at 9.8m/s surely if u where to fire a gun at 9.8m high the bullet would hit the ground in 1 second ? which it in RE it dose not.
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Re: bullet bullistics.
« Reply #1 on: December 21, 2007, 02:25:30 PM »
When you fire a bullet parallel to the ground it travels very fast, it slowly starts to come to earth due to the upwards acceleration of the earth.

yea, but in FE if i fire a rifle 9.8m off the ground wouldn't the bullet hit the ground in 1 second ?
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Tom Bishop

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Re: bullet bullistics.
« Reply #2 on: December 21, 2007, 02:27:48 PM »
Quote
yea, but in FE if i fire a rifle 9.8m off the ground wouldn't the bullet hit the ground in 1 second ?

Yes. Luckily the bullet is pretty fast and covers a lot of ground in that one second, as to make the drop unnoticeable.

"Gravity" makes bullets drop towards the earth at 9.8 m/s2 as well.
« Last Edit: December 21, 2007, 02:31:48 PM by Tom Bishop »

Re: bullet bullistics.
« Reply #3 on: December 21, 2007, 02:31:55 PM »
i assume cpt_bthimes is military ? because im sure at a hight of 9.8m a bullet would travel for more than 1s. ill try find some proof.
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Re: bullet bullistics.
« Reply #4 on: December 21, 2007, 02:50:35 PM »
check this. using the calculations on this site:

http://www.worsleyschool.net/science/files/bullet/trajectory.html

"This result tells us that a rifle bullet, when fired or dropped from a height of about 5 feet, will take just over half a second to hit the ground. This time won't change if the bullet is fired with a higher velocity."

now 9.8m =  32.152231 feet (source)

32/5= 6.4

0.5 x 6.4 = 3.2 seconds.

so fireing a bullet at a elevation of 9.8m would take 3.2s to hit the ground, not 1.

im not very good at maths, so say if i got it all wrong.
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cpt_bthimes

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Re: bullet bullistics.
« Reply #5 on: December 21, 2007, 02:59:29 PM »
sorry tommo, but this has to be said, for only the second time in history, ever: bishop is right.

no matter the caliber or the velocity (to a point), firing a rifle parallel to the ground, the bullet hits the ground at (about) the same time as dropping one.  i say "about" because there are various aerodynamic forces at work as well.

this is why sniper rifles have disproportionately more powder than slug: to maximize muzzle velocity, e.g. get the sucker to it's target as fast as possible.  subsonic smgs are great for urban spec ops, because they can be silenced (much, much more quiet than in the movies - all you hear is the cycling, like a paintball gun).  but you never see silenced long-range sniper rifles.  (except in the movies.)  because you can't silence the sonic boom of supersonic munitions, e.g. nato 5.56 round as standardized on by most western forces (e.g. m4 and some sniper rifles).  the .50 caliber barret m107 is another legendary example.

as with all sniper (and hunting) rifles, you still have to adjust for elevation depending on the distance to target.  for a target at your same elevation 1,000 meters away, you literally wind up aiming up (though not so simply).  incredibly high-velocity rifles can place a round unbelievably far away, but adjustments for elevation become increasingly more absolutely critical.  (as with compensating for other factors such as wind and temperature.)

theoretically on a round earth, if you can ge enough muzzle velocity, you could place a round in orbit just by firing it prallel to your local plane.  but doing that realistically would just not be possible: the round would disintegrate because you couldn't accelerate it gently enough in a barrel of reasonable length, to reach it's required exit velocity.  as pointed out elsewhere recently, the "superguns" of wwi had to take the curvature of the earth into account.

Re: bullet bullistics.
« Reply #6 on: December 21, 2007, 03:01:59 PM »
check this. using the calculations on this site:

http://www.worsleyschool.net/science/files/bullet/trajectory.html

"This result tells us that a rifle bullet, when fired or dropped from a height of about 5 feet, will take just over half a second to hit the ground. This time won't change if the bullet is fired with a higher velocity."

now 9.8m =  32.152231 feet (source)

32/5= 6.4

0.5 x 6.4 = 3.2 seconds.

so fireing a bullet at a elevation of 9.8m would take 3.2s to hit the ground, not 1.

im not very good at maths, so say if i got it all wrong.


was this all wrong then ?
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cpt_bthimes

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Re: bullet bullistics.
« Reply #7 on: December 21, 2007, 03:05:39 PM »
i don't know, i hate working through formulas.  that doesn't mean you didn't do a good job with due diligence; i'll let someone else work out what's wrong or potentially wrong (or not wrong).

Re: bullet bullistics.
« Reply #8 on: December 21, 2007, 04:16:56 PM »
can some 1 tell if my calculations are wrong ?

that shooting a rifle 9.8m high of the ground would take 3.2s to hit the ground
but FE says it would take 1.
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Re: bullet bullistics.
« Reply #9 on: December 21, 2007, 04:23:03 PM »
your calculations look fine to me

Re: bullet bullistics.
« Reply #10 on: December 21, 2007, 05:02:25 PM »
Equivalence Principle.

Re: bullet bullistics.
« Reply #11 on: December 21, 2007, 05:24:48 PM »
Equivalence Principle.

im not familiar to that.
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cpt_bthimes

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Re: bullet bullistics.
« Reply #12 on: December 21, 2007, 05:57:35 PM »
it's not specific to your posted formula.  it just says that the gravitation and acceleration are indistinguishable.  it was posited by einstein as part of...oh shoot now i'm forgetting which one...special or general relativity.  and generally an accepted principle by re and fe alike.  in other words, the fe'ers are right when they say, "you can't prove what you experience as gravity, isn't actually acceleration".  (in a very limited sense of the argument - ignoring other begged questions.)

aside from the issues of a flat earth accelerating indefinitely (approaching the speed of light within about a year or so), and various other issue like arbitrary application and non-application of the ua (flat earth "universal accelerator") to various objects in the sky,  as a very isolated principle it is fundamentally sound. 

so whether a bullet hits the ground because it was gravitationally attracted to the earth (it "fell"), or because the earth accelerated up to it, by itself is fundamentally indistinguishable and generally not a point of contention.

Re: bullet bullistics.
« Reply #13 on: December 21, 2007, 06:09:34 PM »
so whether a bullet hits the ground because it was gravitationally attracted to the earth (it "fell"), or because the earth accelerated up to it, by itself is fundamentally indistinguishable and generally not a point of contention.

thats the thing though, the equation i did shows that at 9.8m high when fired a bullet would take 3.2s to hit the ground when gravity is used, but in UA it would be 1 second.
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cpt_bthimes

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Re: bullet bullistics.
« Reply #14 on: December 21, 2007, 06:19:01 PM »
huh.  don't know why then.  theoretically they should be the same.  neither you, me, a spinning slug, or the air it is whizzing through should be able to tell any difference whatsoever between gravity or acceleration.  in fact the formula(s) should be completely independent of which one it really is  if no one responds to your formulas, or the discrepancies you've found, i'll take a look at them sometime this weekend and see if i can find what's wrong (or right, etc.).  not that i am necessarily smarter than you or anyone else here.  but who knows, maybe a different viewpoint will help.

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Jack

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Re: bullet bullistics.
« Reply #15 on: December 21, 2007, 06:59:59 PM »
UNDER THE Y-COMPONENT:

If the height is 9.8m,

d = vit + Żat2

Since we are dealing with the Y-component, the initial velocity in the Y-direction will be zero. The rifle is fired horizontally at 300m/s,.

d = Żat2

Now, isolate and find t,

t = √((2d)/a) with a = UA

t = √((2*9.8m)/(9.8m/s2))

t = 1.41s

Thus, in both FE and RE, the time it takes the bullet to hit the ground from a height of 9.8m is 1.41s. No matter how fast the bullet is fired, the time remains the same because Y-component is independent from X-component. This scenario neglects air resistance, friction, and energy.

UNDER THE X-COMPONENT:


d = vit + Żat2

Now, if we want to find the range the bullet has traveled. Since there is no vertical acceleration (or gravity) in the horizontal direction, a is neglected.

d = vit

d = (300m/s)(1.41)

d = 423m

The range the bullet has traveled is 423m before it hits the ground.
« Last Edit: December 21, 2007, 07:14:34 PM by Jack. »

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TheEngineer

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Re: bullet bullistics.
« Reply #16 on: December 21, 2007, 11:41:01 PM »
now 9.8m =  32.152231 feet (source)

32/5= 6.4

0.5 x 6.4 = 3.2 seconds.

so fireing a bullet at a elevation of 9.8m would take 3.2s to hit the ground, not 1.

im not very good at maths, so say if i got it all wrong.

I have no idea what it is you did.  You really should include units.  I can see you divided a distance by a distance and then divided this by 2.  Why?


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TheEngineer

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Re: bullet bullistics.
« Reply #17 on: December 21, 2007, 11:41:58 PM »
aside from the issues of a flat earth accelerating indefinitely (approaching the speed of light within about a year or so)
You've been here how long and you still have this problem?


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Re: bullet bullistics.
« Reply #18 on: December 22, 2007, 06:51:52 AM »
now 9.8m =  32.152231 feet (source)

32/5= 6.4

0.5 x 6.4 = 3.2 seconds.

so fireing a bullet at a elevation of 9.8m would take 3.2s to hit the ground, not 1.

im not very good at maths, so say if i got it all wrong.

I have no idea what it is you did.  You really should include units.  I can see you divided a distance by a distance and then divided this by 2.  Why?

what i did was after seeing the calculations on the website that said a bullet would hit the ground in 0.5 seconds if fired 5 feet high i calculated how many feet was in 9.8m (32.15...feet) i then divided 32 feet by 5 feet to see how many times higher my wanted hight (9.8m or 32.15...feet) was from 5 feet which = 6.4 times higher. then x 6.4 to 0.5 (the time taken at 5 feet) to find out the time taken at 32 feet(9.8m)

like i said, im not the best at maths, so if its all wrong please point out where i went wrong.
« Last Edit: December 22, 2007, 06:59:23 AM by tommo »
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Re: bullet bullistics.
« Reply #19 on: December 22, 2007, 06:59:02 AM »
UNDER THE Y-COMPONENT:

If the height is 9.8m,

d = vit + Żat2

Since we are dealing with the Y-component, the initial velocity in the Y-direction will be zero. The rifle is fired horizontally at 300m/s,.

d = Żat2

Now, isolate and find t,

t = √((2d)/a) with a = UA

t = √((2*9.8m)/(9.8m/s2))

t = 1.41s

Thus, in both FE and RE, the time it takes the bullet to hit the ground from a height of 9.8m is 1.41s.

now, one of you guys is wrong, the web site calculates 5 feet to be 0.5 seconds and 9.8m is 32 feet. and 32 feet is 6.2 times as high as 5 feet, so the answer from 5 feet (0.5) x 6.2 gives you the answer from 32 feet(9.8m) which = 3.2s

also about you'r answer, with the earth accelerating up at 9.8ms if the shooting hight was 9.8 it would take 1s , not 1.41s
« Last Edit: December 22, 2007, 07:00:38 AM by tommo »
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cpt_bthimes

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Re: bullet bullistics.
« Reply #20 on: December 22, 2007, 09:59:31 AM »
regardless of which result is right (and just because there is an online formula doesn't mean it's right), i'm still not understanding why you would think a bullet takes a different time to hit the ground depending on whether it's gravity or earth's acceleration causing it to do so.  (or even if that is what you're thinking.  are we just now trying to get the figure right, regardless of what is causing it?)

the forumula on the website just uses "g".  which could be gravitation, or earth's acceleration, equivalently.

Re: bullet bullistics.
« Reply #21 on: December 22, 2007, 10:24:16 AM »
regardless of which result is right (and just because there is an online formula doesn't mean it's right), i'm still not understanding why you would think a bullet takes a different time to hit the ground depending on whether it's gravity or earth's acceleration causing it to do so.  (or even if that is what you're thinking.  are we just now trying to get the figure right, regardless of what is causing it?

i was trying to find out if there is a difference between the bullet air time in gravity and acceleration, and i thought i got it, FE says 1s RE says 3.2s.
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cpt_bthimes

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Re: bullet bullistics.
« Reply #22 on: December 22, 2007, 10:29:44 AM »
how are you isolating "g due to gravitation" [presumably re], and "g due to earth's acelleration" [presumably fe]?

edit:

actually i can think of one difference between the two models.  maybe this is what you were trying to say all along, i don't know.  in the fe model, the earth is flat.  in the round re, the earth is...well, round.  we could ignore the *cause* of g for now, and just take the earth's curvature into effect.  in that case, especially with a very high-velocity - but realistically so - rifle (say a .22-250 varmint gun), the curvature of the earth may well come into play. 

the simple formula for dropping something would only be completely accurate for a slug when fired parallel to a flat earth.  on a round earth, when fired parallel to the local plane, means the earth will curve away from underneath the bullet as it travels "horizontaly" and falling "vertically".  (which is literally what "orbit" means - perpetual free-fall but the more you fall, the more the earth curves away underneath you).  but since the projectile doesn't have enough velocity to reach sustained orbit, it ultimately falls faster than the earth curves away, and lands on the ground.

that would definitely take more time, than dropping a bullet from your hand at the same time.  and would indeed be good proof.  is that what you have been trying to say all along?  if so, this has little to do with the cause of g.

what might be harder to separate out, however, is aerodynamic effects, which might be used to explain keeping the madly spinning slug aloft.  (like a spinning dimpled golf ball although not spinning the same way.)  if fe'ers were to accept the objective measurments of a fired bullet taking longer to hit the ground than a dropped one, the would surely use aerodynamic forces as an "explanation".  and also, not even re'ers could rule out "local" curvature of the earth, say a huge miles-wide plateau that was imperceptibly dome-shaped.  maybe if performed over water...
« Last Edit: December 22, 2007, 10:45:16 AM by cpt_bthimes »

Re: bullet bullistics.
« Reply #23 on: December 22, 2007, 10:37:07 AM »
how are you isolating "g due to gravitation" [presumably re], and "g due to earth's acelleration" [presumably fe]?

i don't know, im no good at maths, i just said (and tom bishop agreed) that in FE shooting a bullet  on a plain to the ground at 9.8m high would take 1 second to hit the ground, but then did the maths of that website and it said 3.2s not 1s.
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cpt_bthimes

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Re: bullet bullistics.
« Reply #24 on: December 22, 2007, 10:53:10 AM »
see my extra comments above which i didn't save until after your previous post.

i looked again at the website and saw no constants or variables for curvature of earth.  so, this does not support my argument of the extra time being due to that.  (which of course doesn't invalidate my [somewhat obvious] hypothesis.)

another problem i noticed with that website is that it is not solving a problem forwards, it is solving it backwards. the outcome is already assumed, even explicitly so: that both will hit the ground at the same time.  the math is merely the reverse-engineered solution of the already concluded premise. 

even i as an re'er have a problem with that - at least, in the context of a debate which calls into question one of the direct products of a function with a predetermined outcome.

so for now i think it just boils down to either accepting that nothing is proven or disproven and moving on, or trying to find the source of the discrepancy which you have pointed out.  (and keeping in mind that finding that discrepancy could ultimately do nothing to prove or disprove on earth model over the other...)

Re: bullet bullistics.
« Reply #25 on: December 22, 2007, 12:47:44 PM »
ok fair enough. i was just trying to see if UA would effect a bullet different from gravity. but seems FET made up UA well  ;)
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Bushido

Re: bullet bullistics.
« Reply #26 on: December 22, 2007, 01:16:47 PM »
when you fire a bullet parallel to the ground it travels very fast, it slowly starts to come to earth due to gravity (RE) (among other things.)

but in FE, with the earth travelling up at 9.8m/s surely if u where to fire a gun at 9.8m high the bullet would hit the ground in 1 second ? which it in RE it dose not.

Actually, it will hit the ground in 1.4 s. The Earth is acceleratimg upwards with acceleration (according to an observer on the Earth) g = 9.8 m/s2

Re: bullet bullistics.
« Reply #27 on: December 22, 2007, 01:48:54 PM »
Just thought I'd wade in on this one.
The bullet in FE and RE will for all intents and purposes hit the ground at the same time.In theory if the Earth was perfectly spherical in RE it would take a poofteenth longer due to curvature, but local variations at that scale will over ride that result.
A proof of RE is with ballistics though.
FE theory cant explain Orbital or Escape velocities.They just say they don't exist (problem solved)
IE in RE even at 9.8m  above ground level if your round had sufficient muzzle velocity and you had the correct elevation the round will never hit the ground (excluding external unbalanced forces like friction).
I think at these parameters in FE you take out a Ice Guard  ;)

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Jack

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Re: bullet bullistics.
« Reply #28 on: December 22, 2007, 02:16:13 PM »
now, one of you guys is wrong, the web site calculates 5 feet to be 0.5 seconds and 9.8m is 32 feet. and 32 feet is 6.2 times as high as 5 feet, so the answer from 5 feet (0.5) x 6.2 gives you the answer from 32 feet(9.8m) which = 3.2s
That's wrong. Since this is a projectile motion situation, you should be using d = vit + Żat2.

also about you'r answer, with the earth accelerating up at 9.8ms if the shooting hight was 9.8 it would take 1s , not 1.41s
No, it is 1.41s. Either you're trying to disprove physics calculations or just assuming that since the Earth accelerates 9.8m/s at 1s, the Earth will hit the bullet at 1s if it is dropped or fired from 9.8m.

Re: bullet bullistics.
« Reply #29 on: December 22, 2007, 02:50:28 PM »
now, one of you guys is wrong, the web site calculates 5 feet to be 0.5 seconds and 9.8m is 32 feet. and 32 feet is 6.2 times as high as 5 feet, so the answer from 5 feet (0.5) x 6.2 gives you the answer from 32 feet(9.8m) which = 3.2s
That's wrong. Since this is a projectile motion situation, you should be using d = vit + Żat2.

also about you'r answer, with the earth accelerating up at 9.8ms if the shooting hight was 9.8 it would take 1s , not 1.41s
No, it is 1.41s. Either you're trying to disprove physics calculations or just assuming that since the Earth accelerates 9.8m/s at 1s, the Earth will hit the bullet at 1s if it is dropped or fired from 9.8m.

I 100% agree with Jack , tommo.
Your confusing velocity and acceleration.
If something is accelerating at 9.8m /s/s after 1 sec it is traveling at 9.8m/s but it started at 0m/s so it must take longer than 1 sec to travel 9.8m.
s=ut+1/2at2 is the correct formula

s=distance traveled
u=initial velocity
a= acceleration
t=time

so:
9.8=0+(0.5*9.8*t2)
9.8=4.9*t2
2=t2
time in seconds =1.41