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KE and Momentum ??

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KE and Momentum ??

Old 02-09-2009, 07:58 AM
Fork Horn
Thread Starter
Join Date: Dec 2006
Location: Central Wisconsin
Posts: 494
Default KE and Momentum ??

Ok, not the guru that you guys are. i want to figure my KE and momentum numbers. here is my setup:
2004 Bowtech Patriot single cam
DL 28.5
DW 71#
Loop and meta peep onstring
Arrow Axis 340's(black 9.9gpi) 27" long with 4" wraps and 2" blazers
Any other info that I need?
dandbuck is offline  
Old 02-09-2009, 09:52 AM
Join Date: Feb 2006
Location: Kodiak, AK
Posts: 2,877
Default RE: KE and Momentum ??

KE = 1/2 M (mass or in this case weight of the projectile) x V (velocity or in this case speed of the projectile) ^2 (squared)
Momentum = MV (the velocity is not squared in this case nor is the resultant halved).

So in order to figure them you'll need a grain scale to weigh your arrow and a chronograph to measure their speed.
In this case your mass will be in grains and your velocity will be in fps so to get those units to lb. ft. of KE you use:
lb. ft. = (grains)(fps x fps)/450240

While I don't agree 100% with everything written in the article, I'm in agreement with most of it. Here's a handy calculator that let's you just plug in the numbers:

Here's another related but much more scientific discussion of the two by a bunch of physicists:
(Pay particular attention to what mordechai9 has to say, I think he hits it square on the head.)
KodiakArcher is offline  
Old 02-09-2009, 10:11 AM
Fork Horn
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Join Date: Dec 2006
Location: Central Wisconsin
Posts: 494
Default RE: KE and Momentum ??

Thanks Kodiak!
That helps a bunch. It looks like I would have 63# of KE using that formula I have beedn getting around 284 fps out of my bow, but i used 275 for calculations since I don't know how good the chrony was. I also figured 5 grains for the nock and 9.9 per inch for the axis.
dandbuck is offline  
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