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Thread: formula for KE

  1. #1
    Join Date
    Nov 2003
    Location
    Chihuahua, Mexico
    Posts
    3,122

    formula for KE

    whats the formula for KE ???



    i belive its 1/2 mass times the squared of the speed, am i right??

    because if im right, i think that speed would be more important than mass, because the speed is squared and mass is divided.

    so, this leads me to think that a lighter, faster arrow would have more KE than a heavy, slower arrow. of course that a heavy and fast arrow would have the most KE. right or wrong??

    i have had this questions for some time now, and i think its time someone points me in the right direction.

    thanx for your help
    I got a bow for my girlfriend... best deal ever!!


  2. #2
    Join Date
    Jun 2003
    Location
    Waco, Texas
    Posts
    19,193
    There have many discussions about this subject and doubtlessly there will be many more...

    Here are a few good articles about arrow penetration, kinetic energy and momentum...

    http://homepage.ntlworld.com/joetapley/target.htm

    http://home.att.net/~sajackson/ke.html

    http://www.alaskafrontierarchery.com/Articles.html

  3. #3
    Join Date
    May 2003
    Location
    Alton, IL
    Posts
    3,522

    Let me help you out...

    Here is the formula you need to figure out the KE of your arrow.

    Let me first give you mine. I shoot both the carbon express terminator hunters at 487 grains and the easton axis arrows at 435 grains.

    Carbon Express:
    246 fps x 246 fps x 487 grains/450240 = 65.4 KE

    Easton Axis arrows:

    260 fps x 260 fps x 435 grains/450240 = 65.3 KE

    The heavier arrow carries more KE shot from the same bow at the same poundage, but the speed will be higher for the lighter arrow and an insignificant amount of KE lost.

    Contact Javelina on this site and he'll give to you the formula for momentum. This is more important for your information in shooting animals with arrows.

    My momentum for the carbon express was equal to .54 or something like that.

    BACK TO YOUR QUESTION:

    Is speed more important than weight--no
    Is weight more important than speed--no

    Are both equal in consideration--MY OPINION--yes.

    Lets look at shooting an arrow for grins and giggles using my bow weight of 85#'s. Lets say that I'm pretty insane and want to shoot an arrow about 4 grains per pound. Thats an arrow that weighs 340 grains. Lets use for the sake of an insane arguement an arrow that weighs 350 grains.

    Here we go. Lighter arrow at 350 grains = 277 fps.
    (by the way I have a 26" draw)

    277 fps x 277 fps x 350/450240 = 59.6 lbs of KE.

    Now obviously I would not shoot an arrow that was only 4 grains per pound but I used this to compare what a light arrow would do in KE vs. an heavier arrow.

    I love both my arrows and even though I have not shot anything with the axis arrows they still out penetrate my heavier carbon express arrows.

    With that said, on October 15, 2003 I shot my very first buck in my very first year hunting at 38 yards with a complete pass thru using the heavier arrows.

    Don't know if I answered your question, but that's my take on it.

    I feel I have a great balance between speed and weight.

    Paul
    "As the deer pants for streams of water, so my soul pants for you, O God" (Psalm 42:1, NIV).
    3rd BTN, 9th Marines---Semper Fi!!!
    2010 Elite Judge 70# @ 26"...415 grain arrow at 275 FPS for 69#'s of KE.
    67 1/4" Osage Self bow 51#'s @ 26"
    Paulie G. http://www.vortexoptics.com/

  4. #4
    I have always used the formula that Newhunter is talking about . This formula works great . Want to see a good thread on kenetic energy ? Check out this one Javi posted http://www.archerytalk.com/vb/showt...&threadid=50169

  5. #5
    Join Date
    May 2004
    Location
    Jacksonville, Arkansas
    Posts
    103

    Thanks for the formula

    Thanks, I have been looking for a good way of finding the KE. Somewhere that has to be a happy medium... haha

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