Home Forums Hunting & Shooting Ask The Gunwriters formula

Kinda' off topic,
<br>Could you give me the formula for figuring kinetic energy,please?
<br>All that school time was obviously wasted!
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<br>We had a poster on another board ask a guy if he would rather be hit with a 600 gr. bullet at 1000 fps. or an ounce of photons at the speed of light.
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<br>I said it would depend on how densely packed the photons were.
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<br>Sorta' like the steel/lead shot deal, if your projectile is less dense you need more velocity to develope the same energy.
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<br>TIA
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Let
<br>v = velocity in feet per second
<br>w = bullet weight in grains
<br>e = energy in foot-pounds
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<br>e = w times v times v, divided by 450,436
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<br>1. Multiply the velocity by the velocity ("v squared").
<br>2. Multiply "v squared" by the bullet weight.
<br>3. Divide the result by 450,436 (conversion factor for grains to pounds and weight to mass)
<br>4. Round-off to four figures.
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<br>Here and there, you'll see the conversion factor given as 450,200, 450,250, etc, indicating that the gravity element of the conversion had been rounded-off individually before the single, combined conversion factor was calculated. You can even use the conversion factor rounded-off to 450,000 and produce an energy figure that's very close -- after you round it off -- to any figure you derive with a more-accurate conversion factor.
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<br>The conversion multiplier 1/450,436 is a combination of 1/2g (1/2 times gravity -- 1/2 x 32.174) and the conversion of grains to pounds, 1/7,000 (one grain is 1/7,000 pound). Some writers round the g figure off first -- to 32.17 or 32.2, or even 32.0, for example. Where you round-off doesn't matter enough to the final four significant figures to fuss or fret about.
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<br>For example, the kinetic energy (potential energy by virtue of its mass and speed) of a 150-grain bullet striking at 2,300 ft/sec --
<br>v squared (v times v) = 5,290,000
<br>5,290,000 times w = 793,500,000
<br>793,500,000 divided by 450,436 = 1,761.626513 (most-accurate e)
<br>1,761.626513 rounded-off to four significant figures = 1,762 ft-lb
<br>or
<br>793,500,000 divided by 450,000 = 1,763.33333333333333 ft-lb (least-accurate e), which rounds-off to 1,763 ft-lb
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<br>The difference is only 2 ft-lb, only about 1/10 of 1% of the more-accurately calculated figure.
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<br>As matter of practical fact, the impact velocity of 2,300 ft/sec is usually (a) an approximation, a guess, and (b) probably not the actual impact velocity anyway. So either figure for the energy is as good a guess as the other, for what the actual impact energy is. Also, not all of the potential (kinetic) energy of the bullet is usefully imparted anyway. Some is wasted on making the thump or splat sound of impact. So as a practical matter, the last three figures in the conversion factor -- the xxx in 450,xxx -- don't matter much.
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a correction, with my apologies and an explanation --
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<br>The conversion factor above is the old one, based on the old figure for gravity. Here (below) is the letter that I wrote to one of my writer friends a few years ago, explaining my correction of the conversion factor that he'd used in the book manuscript that I was editing. As I said above, the value that you use for the xxx in 450,xxx doesn't matter much for all practical use -- but I like to be as precise as I can, whenever I can.
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<br>Here's my letter. (The symbolic notation for "v squared" printed correctly in my letter to R_____ but comes out as "v2" below instead of the correct "v" with a superscript "2" -- a limitation of the text editor this board uses -- sorry 'bout that.)
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<br>R_____:
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<br> I don't expect you to remember all this, but just so you can see that the constant in your energy equation is a six-figure number with a comma where you put a decimal:
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<br> The basic physics equation for the potential (kinetic) energy of a moving body is e = (mv2) � 2g when e is in foot-pounds, m is in pounds, and g is the acceleration of gravity in feet per second per second. But g is not a constant "constant," and people who calculate the conversion factor 450,xxx don't all (a) use the same value for g or (b) consistently round-off the numbers they use to calculate the conversion factor.
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<br> Gravity accelerates falling objects 9.78 meters per second per second at sea level at the equator and 9.83 m/sec/sec at sea level at the north pole. Between these two extremes, the acceleration from gravity varies also with elevation above mean sea level � 9.80 m/sec/sec at New York (0 ft MSL), 9.79 m/sec/sec at Denver (5,400 ft MSL), 9.78 m/sec/sec on Pike's Peak (14,100 ft MSL), for example. So we need a compromise approximation for g.
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<br> The average of the two extremes is 9.805 m/sec/sec.
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<br> One meter is 3.280833333 feet.
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<br> So gravity's average acceleration in feet per second per second is (carried-out unreasonably far) about 32.16857083 ft/sec/sec. (Some round it off to 32, others to 32.2, with takers at points between.) A close approximation is 32.17 ft/sec/sec.
<br>The equation doubles it to 64.33714166 ft/sec/sec, carried-out, or 64.34 as a close approximation.
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<br> The basic equation uses pounds for the mass (here, essentially the same as its weight) of the moving body. One pound comprises 7,000 grains. So the weight of the bullet in pounds is its weight in grains divided by 7,000.
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<br> The six-figure "constant" lets us use grains directly and not have to figure-in gravity. It combines the conversion of grains to pounds and the value of gravitational acceleration: 7,000 � 64.33714166 = 450,359.9916.
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<br> In use, this inconstant "constant" ranges from 450,240 to 450,400, depending on where the folks who calculate it have rounded-off their working numbers. The best place to round it off? Who can say? Using 32.17 for g, the "constant" becomes 450,380, the figure I put in your Chapter 7 equation.
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<br> Remember that the velocity figure is (a) an average of the velocities of x rounds and (b) squared in the equation. Where's the best place to round-off the downrange velocity, which is an estimation based on the rounding-off of other numbers that "describe" the bullet and its behavior? To the nearest hundred feet per second? The nearest fifty? The nearest ten is unreasonably tight. We could probably use a constant of 450,000 and not be off far enough to matter much.
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<br> So "exact" ain't exact, is it?

... and if you ever wondered what the "real" value of pi is, here's the greatest number of decimal places that I've seen pi carried out to --
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<br>3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37511
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<br>That's FIFTY decimal places -- oughta thrill you right down to your socks and garters if you're one of those birds who tweet and chirp happily on trivia!
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Ken Howell; It dawned on me that you could help me with a question. It has been claimed that the Bible states that the the value of PI is 3 even. Cpould you tell me where to find that?.
<br> Another point about formulas, rounding off ect; With products the accuracy of the answer can be no more accurate than any of the terms. If your bullet is measured with three digits for example, G need only be three digits. It is the curse of the calculator that answers may now be given to 10 places.
<br>Good Luck!
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If pi ever came-up in my study of the Bible, I didn't notice. Have no idea where to find it, if indeed it's in there.
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<br>I prefer to calculate to more than the number of significant figures, to know what to round the last significant figure off to. Rounding-off is always my last step, never a first or interim step.

Ken,
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<br>One of my old engineering professors had memorized PI to 200 places - way more than useful. I also had another prof. (a brilliant man, by the way) who characterized it as follows:
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<br>Physicists use pi as 3.141592654
<br>Scientists use pi as 3.14159
<br>Engineers use pi as 3.14
<br>and
<br>Engineers in a hurry use pi as 3

" ... memorized PI to 200 places ...." Easy to claim, harder to check. Somehow reminds me of the fellow who became a living legend to the other regular passengers on a certain commuter train to New York years ago. He occupied his time on each Monday-morning ride by doing the crossword puzzle in the Sunday Times -- notorious for its difficulty and the erudition it demanded -- rapidly, IN INK. Finally, one Monday morning, another passenger picked it up after he'd dropped it on his seat and left the train --
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<br>-- and found that he'd filled all those squares with gibberish -- just letters, not words.
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<br>Your prof was probably an honest man. He also reminds me of the time when Henry Ford told plant visitors "That automobile is made with four thousand, five hundred, and sixty-seven parts" (or whatever the number was). A visitor asked one of Ford's engineers or designers whether that were true.
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<br>"I have no idea," the engineer said. "I can't imagine a more useless bit of information."

Ken,
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<br>In today�s trend to avoid obscurity through inane feats, memorizing pi to 200 decimal places is hardly noteworthy. There is actually a worldwide �contest� to memorize pi to the most significant places. Currently the world record holder can spout off, under verifiable conditions, over 40,000 digits of that favored Greek letter. I suppose it�s the same drive (albeit a mental one) that causes the mountain climber to desire to climb Everest. However, at least Everest has a pinnacle to measure success and does not extend to infinity as does PI. My professor had stopped trying in the 1970�s when he learned his meager 200 decimal places had been bested by five fold.
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<br>You can see the list of current PI champions at the link below
<br>Pi Rankings
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"over 40,000 digits of that favored Greek letter"

But can he tie his own shoe laces?

The passage most people refer to when they talk about pi being 3.0 in the Bible describes the way Hiram of Tyre constructed the huge basin, or "sea," for Solomon's Temple. Try I Kings 7:23:

"Now he made the sea of cast metal ten cubits from brim to brim, circular in form, and its height was five cubits, and thirty cubits in circumference."

Oh--and about significant figures: if what you're doing is multiplication and division, you really only need to carry around two or three spare significant figures through your calculation, unless it has a really large number of steps. It's addition and subtraction, particularly of numbers with greatly differing magnitudes, that can bite you in the backside if you're careless with significant figures.

Nevermind it helps to read before you open your mouth <img src="/ubbthreads/images/graemlins/blush.gif" alt="" />

An ounce (438gr) of photons at the speed of light? Hmm. Near the speed of light relativistic effects become important, so you can't really use the Newtonian physics that ballisticians depend on.

But if you could, you'd be comparing 1330 foot-pounds with 938,000,000,000,000 foot-pounds.

Don't make your decision yet, though, because relativistic time dilation and the Lorentz contraction lead to an increase of mass near lightspeed, which would affect the computation.

It'd probably be best just to use E=mc^2.

I suppose that one could stand naked in the sun all day and then submit to being shot with that 600 gr. bullet. I suggest that the experiment be accomplished in the order listed, though. ;-)

My calculations suggest that your brain travels at the Speed of Light.
One second it's here and the next, it's 186,000 miles away!

At least he’s not bumping 18 year old nonsense threads

Lol……I wonder if he noticed……..

Pie r square = crazy

Pie r round. Cornbread is square.

...Unless your using cast iron to cook with.

Pizza is round but comes in square boxes.

......... and cut into triangles