Comments on: Arrow Kinetic Energy and Momentum: what they mean to the archer http://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/ Bows, arrows, physics and more! Everything for the archery and bowhunting enthusiast Fri, 18 May 2012 06:17:05 +0000 hourly 1 http://wordpress.org/?v=3.3.2 By: Rick Parkerhttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-19043 Rick Parker Fri, 27 Apr 2012 20:30:11 +0000 http://archeryreport.com/?p=1925#comment-19043 Thanks Michael for your effort in all of this. I killed a bull elk with the set up I mentioned above last season. I missed all bone and had most of the arrow penetrate thru the off side. 38 yard broadside shot. I hit him a little far back but was blessed and took out the main artery. He went 50 yards and tipped over. I am going to try adding some weight tubes to my current arrow setup to see how I like them. At 3 gr/inch they will put me right up near your set up @478 gr. Thanks Michael for your effort in all of this. I killed a bull elk with the set up I mentioned above last season. I missed all bone and had most of the arrow penetrate thru the off side. 38 yard broadside shot. I hit him a little far back but was blessed and took out the main artery. He went 50 yards and tipped over. I am going to try adding some weight tubes to my current arrow setup to see how I like them. At 3 gr/inch they will put me right up near your set up @478 gr.

]]> By: SCOTThttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-16361 SCOTT Thu, 22 Mar 2012 15:51:35 +0000 http://archeryreport.com/?p=1925#comment-16361 Oh sorry bout the caps i wasnt shouting, work computer is set up that way and i never changed it. I will check out that article. Oh sorry bout the caps i wasnt shouting, work computer is set up that way and i never changed it. I will check out that article.

]]> By: Michael Larsenhttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-16359 Michael Larsen Thu, 22 Mar 2012 13:33:57 +0000 http://archeryreport.com/?p=1925#comment-16359 Scott, a couple of different things in your case: first, were each of the arrows tuned properly and did you check that they were? If so, how? Changing from arrow to arrow can drastically change the tune of the bow/arrow combination and result in a loss of efficiency. Also, foam acts differently in stopping arrows than most other media. I have seen faster arrows with less KE and momentum penetrate better than heavier/slower arrows with more KE and momentum. My working theory is that the foam closes up around an arrow at a certain velocity and the faster arrows are able to penetrate more than slower arrows before the friction of the closing foam stops the arrow. See this article for more: http://archeryreport.com/2010/01/friction-penetration-archery-target-animal-penetration/ BTW, please refrain from typing in all caps. It's more difficult to read and there is no need to shout ;) Scott, a couple of different things in your case: first, were each of the arrows tuned properly and did you check that they were? If so, how? Changing from arrow to arrow can drastically change the tune of the bow/arrow combination and result in a loss of efficiency. Also, foam acts differently in stopping arrows than most other media. I have seen faster arrows with less KE and momentum penetrate better than heavier/slower arrows with more KE and momentum. My working theory is that the foam closes up around an arrow at a certain velocity and the faster arrows are able to penetrate more than slower arrows before the friction of the closing foam stops the arrow. See this article for more: http://archeryreport.com/2010/01/friction-penetration-archery-target-animal-penetration/

BTW, please refrain from typing in all caps. It’s more difficult to read and there is no need to shout ;)

]]> By: SCOTThttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-16320 SCOTT Wed, 21 Mar 2012 18:13:28 +0000 http://archeryreport.com/?p=1925#comment-16320 I LIKE THE CHARTS AND ALL THE MATH, SEEMS TO BE CLOSE. REAL WORLD TEST, I TOOK ONE ARROW 400 GRAINS AND ANOTHER 313 GRAIN, SHOT BOTH OUT OF SAME BOW. 313 GRAIN ARROW SHOT 330 FPS, 400 GRAIN ARROW SHOT 291 FPS, SHOT BOTH ARROWS INTO SAME TARGET, A 3 FOOT HIGH BEAR TARGET, FIRST SHOT BOTH OF THEM AT 20 YARDS, THE 313 GRAIN ARROW SUNK 11 INCHES INTO TARGET, 4 SEPERATE SHOTS OF SAME ARROW. THE 400 GRAIN ARROW SUNK 10.5 INCHES IN TARGET SAME 4 SHOTS, WENT TO 33 YARDS AND 313 GRAIN 9.25 INCHES 400 GRAIN ARROW 8.5 INCHES. MATH DOESNT SEEM TO ADD UP. I LIKE THE CHARTS AND ALL THE MATH, SEEMS TO BE CLOSE. REAL WORLD TEST, I TOOK
ONE ARROW 400 GRAINS AND ANOTHER 313 GRAIN, SHOT BOTH OUT OF SAME BOW. 313 GRAIN ARROW SHOT 330 FPS, 400 GRAIN ARROW SHOT 291 FPS, SHOT BOTH ARROWS INTO SAME TARGET, A 3 FOOT HIGH BEAR TARGET, FIRST SHOT BOTH OF THEM AT 20 YARDS, THE 313 GRAIN ARROW SUNK 11 INCHES INTO TARGET, 4 SEPERATE SHOTS OF SAME ARROW. THE 400 GRAIN ARROW SUNK 10.5 INCHES IN TARGET SAME 4 SHOTS, WENT TO 33 YARDS AND 313 GRAIN 9.25 INCHES 400 GRAIN ARROW 8.5 INCHES. MATH DOESNT SEEM TO ADD UP.

]]> By: Thomas Petersonhttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-3199 Thomas Peterson Fri, 01 Apr 2011 04:24:17 +0000 http://archeryreport.com/?p=1925#comment-3199 I have found several charts stating what is the sufficient KE for killing different size big game, but is there a chart out there that has the recommended MO (momentum) for killing different sized animals (ie. elk, deer, sheep, moose, ect.)? I have found several charts stating what is the sufficient KE for killing different size big game, but is there a chart out there that has the recommended MO (momentum) for killing different sized animals (ie. elk, deer, sheep, moose, ect.)?

]]> By: Michael Larsenhttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-3084 Michael Larsen Tue, 22 Mar 2011 13:28:43 +0000 http://archeryreport.com/?p=1925#comment-3084 Rick, you've hit the dilemma right on the head. Each archer/hunter needs to decide for themselves where they want to be. Lighter arrows will certainly kill game when placed in the right spot and give a flatter trajectory to help minimize errors in yardage judgment. Heavier arrows will do a better job of penetrating through bone and flesh with the shot isn't perfectly broadside as well as drift less and maintain more energy downrange. I hunt elk in the west where the animals are huge and tough and the distances long so I opt for a 470 grain arrow and practice my yardage judging every chance possible. It's not my job to judge anyone's setup, but rather to just lay the facts out and let everyone decide! Rick, you’ve hit the dilemma right on the head. Each archer/hunter needs to decide for themselves where they want to be. Lighter arrows will certainly kill game when placed in the right spot and give a flatter trajectory to help minimize errors in yardage judgment. Heavier arrows will do a better job of penetrating through bone and flesh with the shot isn’t perfectly broadside as well as drift less and maintain more energy downrange. I hunt elk in the west where the animals are huge and tough and the distances long so I opt for a 470 grain arrow and practice my yardage judging every chance possible. It’s not my job to judge anyone’s setup, but rather to just lay the facts out and let everyone decide!

]]> By: Rick Parkerhttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-3081 Rick Parker Tue, 22 Mar 2011 13:04:27 +0000 http://archeryreport.com/?p=1925#comment-3081 All the math and physics is great up to a point, but how do all the numbers translate to what bowhunters really want to know? If I place my arrow in the kill zone does it have what it takes to effectively and humanely bring down big game? I am shooting a 388 gr arrow 300 fps. This gives me a ke of 77.46 and a mo of .5164. My bow is maxed out (60 lbs) so while I can increase arrow weight speed will decrease accordingly. If I increase arrow weight 100 gr to 488 my speed reduces to about 270 fps. My ke increases to 81 and mo increases to .5845. Does 3.5 lbs of ke and the increase in mo make any real killing difference on deer or elk out to 50 yards at these levels? All the math and physics is great up to a point, but how do all the numbers translate to what bowhunters really want to know? If I place my arrow in the kill zone does it have what it takes to effectively and humanely bring down big game? I am shooting a 388 gr arrow 300 fps. This gives me a ke of 77.46 and a mo of .5164. My bow is maxed out (60 lbs) so while I can increase arrow weight speed will decrease accordingly. If I increase arrow weight 100 gr to 488 my speed reduces to about 270 fps. My ke increases to 81 and mo increases to .5845. Does 3.5 lbs of ke and the increase in mo make any real killing difference on deer or elk out to 50 yards at these levels?

]]> By: Michael Larsenhttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-2750 Michael Larsen Fri, 18 Feb 2011 16:21:06 +0000 http://archeryreport.com/?p=1925#comment-2750 Heya Redneck, Thanks for reading! It would be more accurate to use a gravitational constant of 32.174 instead of rounding up to 32.2 which would result in a denominator of 450436. For illustration purposes and making it easier for people to remember, I usually use the simpler 32.2 and 450800 which is only a difference of about .08%. But since I'm an ultra-anal engineer that has spreadsheets and MathCad workbooks to do my calculations, I actually have a box to compensate for additional, yet extremely minor, losses of gravity due to altitude. In my case I live at about 5000 feet, so the correct value here would actually be 450653. Hardly worth sneezing about, but when you have the computational ability of a computer, why not! Heya Redneck, Thanks for reading!
It would be more accurate to use a gravitational constant of 32.174 instead of rounding up to 32.2 which would result in a denominator of 450436. For illustration purposes and making it easier for people to remember, I usually use the simpler 32.2 and 450800 which is only a difference of about .08%. But since I’m an ultra-anal engineer that has spreadsheets and MathCad workbooks to do my calculations, I actually have a box to compensate for additional, yet extremely minor, losses of gravity due to altitude. In my case I live at about 5000 feet, so the correct value here would actually be 450653. Hardly worth sneezing about, but when you have the computational ability of a computer, why not!

]]> By: High Tech Redneckhttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-2745 High Tech Redneck Fri, 18 Feb 2011 03:43:53 +0000 http://archeryreport.com/?p=1925#comment-2745 Michael, I love this site. I think a more accurate calculation for most of us flatlanders is to use the acceleration due to gravity = 32.16 ft/sec/sec. This yields a denominator of 450240 for the KE calculation. I have seen others use this figure and I believe it applies to locations 1000 ft above sea level. Michael,

I love this site. I think a more accurate calculation for most of us flatlanders is to use the acceleration due to gravity = 32.16 ft/sec/sec. This yields a denominator of 450240 for the KE calculation. I have seen others use this figure and I believe it applies to locations 1000 ft above sea level.

]]> By: Michael Larsenhttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-2743 Michael Larsen Thu, 17 Feb 2011 21:38:37 +0000 http://archeryreport.com/?p=1925#comment-2743 Chris, You may have to enlighten me more because I fail to see where I have contradicted anything you said; in fact you restated exactly what I said! Perhaps I need to work on my wording ;) You can also read a more in-depth discussion of the subject here: http://archeryreport.com/2011/01/heavy-vs-light-arrows-speed-power/ Chris,
You may have to enlighten me more because I fail to see where I have contradicted anything you said; in fact you restated exactly what I said! Perhaps I need to work on my wording ;) You can also read a more in-depth discussion of the subject here: http://archeryreport.com/2011/01/heavy-vs-light-arrows-speed-power/

]]> By: Chris Sholtishttp://archeryreport.com/2009/11/arrow-kinetic-energy-momentum-archer/comment-page-1/#comment-2742 Chris Sholtis Thu, 17 Feb 2011 21:14:56 +0000 http://archeryreport.com/?p=1925#comment-2742 You are not quite correct on your discussion of KE and Momentum of the arrow after the shot. I'd just like to point out that two arrows of identical external dimensions with different velocities have the same drag coefficient (Cd), but the faster arrow will have a higher air resistance (Drag Force) since the drag force equation has the velocity squared in it. The equation is F=0.5*Cd*p*V*V*A (where p is air density, A is cross sectional area, and V is velocity). Just put your hand out the car window while driving to experience this. Your hand dimensions haven't changed, but the force on your hand increases with the speed of the car. Therefore, F=ma does in fact explain why the heavier arrow retains more energy downrange, but it is important to note that the force in this case is not the same for the two arrows. If the drag force were the same, then the distance required to stop the two arrow's flight would be exactly the same for both arrows (even though the lighter arrow decelerates at a higher rate under this scenario, it's mass is also proportionately lower in order for a contant force to be exerted on it). Thanks for all the other great info you've provided, keep up the good work. You are not quite correct on your discussion of KE and Momentum of the arrow after the shot. I’d just like to point out that two arrows of identical external dimensions with different velocities have the same drag coefficient (Cd), but the faster arrow will have a higher air resistance (Drag Force) since the drag force equation has the velocity squared in it. The equation is F=0.5*Cd*p*V*V*A (where p is air density, A is cross sectional area, and V is velocity). Just put your hand out the car window while driving to experience this. Your hand dimensions haven’t changed, but the force on your hand increases with the speed of the car. Therefore, F=ma does in fact explain why the heavier arrow retains more energy downrange, but it is important to note that the force in this case is not the same for the two arrows. If the drag force were the same, then the distance required to stop the two arrow’s flight would be exactly the same for both arrows (even though the lighter arrow decelerates at a higher rate under this scenario, it’s mass is also proportionately lower in order for a contant force to be exerted on it). Thanks for all the other great info you’ve provided, keep up the good work.

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