Kinetic Energy

[Zach Mikita]

What is a good kinetic energy?  Does it depend on the bow and arrow?

[O.L. Adcock]

The best advice is to shoot as much KE as you can accurately! But use it wisely... ...O.L.

[wollelybugger]

Picture a semi full of steel going 40 miles per hour and hitting something. The Ke energy would push the semi forward. The more the weight the harder the push. Now picture a car going twice as fast hitting the same object, not as much Ke energy. The same with arrows.

[Zach Mikita]

Right its simple physics. Ive noticed that even 25 gr impacts the KE with penetration into a target.  I was broad with my question too...I shoot a 55# @28 Kodiak Mag 52" and with a 5575 GT arrow weighing close to 500gr (492) it has 23 lbs of KE.  Is this too low, too high (if there is such a thing), or just right?  This is the arrow that i have bare shaft tuned and it is the closest arrow I have been able to find that flys close to perfect.

[O.L. Adcock]

Zach, For any given bow the KE is "fixed"..It is what it is..Without going to a better bow or higher draw weight you have no choice what it puts out. What I meant by using it wisely, if I shoot a deer with a rubber blunt or a broadhead that barely gets through the far side, I used all the KE I have available in either case. Which choice did I make to use it "wisely"? The BH of course. Some Bh's will be better choices then others depending on the game you are after. You can shoot a heavy arrow at 160 or a light one at 250...Which is the better choice? Depends on what you are trying to do. Much to somes dismay, KE is the only thing our bows put out. KE is the reason a 60# bow should be more "powerful" then a 40#. But we can use a lot of KE in an inefficent way or a little and get the job done. The choices we make are the difference....O.L.

[Zach Mikita]

Ok I really never looked at it that way. It makes sense...a lot of sense    Thanks

[Glenn Newell]

That's fair enough looking at the KE of a bow but wouldn't a much better figure be the momentum of the arrow. At the pointy end of the stick it will be the speed and the weight of the arrow that will dictate penetration. I have seen plenty of times and have been doing it my self for several years now out hunting where lighter bows uing heavy arroews will out pentrate much heavier bows using less grains per pound. Another thing I do is I use a shaft that is narrower than the ferrule of the broadhea, I find this helps a lot with penetration as well...Glenn...

[hawgslayer]

 

Last 2 seasons I put 5 deer in my freezer. All were taken with my Bob Lee T/D HUNTER.
I shoot a 515 gr arrow. It's traveling 165 fps and gave me 31#'s K.E. All the deer were taken under 20 yards and all were double lung pass thru's.
Shot placement is the key!!!!!!!!!  

[O.L. Adcock]

Glenn, "At the pointy end of the stick it will be the speed and the weight of the arrow that will dictate penetration. I have seen plenty of times and have been doing it my self for several years now out hunting where lighter bows uing heavy arroews will out pentrate much heavier bows using less grains per pound."

Oh sure..But where do you get the momentum from?..The KE...Can't have one without the other. We can go up and up in arrow weight and our momentum continues to go up but with the loss of speed. At some point our arrow becomes a stick laying on the ground. "hunting where lighter bows uing heavy arroews will out pentrate much heavier bows using less grains per pound." Sure, but if that heavy bow picked a heavy arrow so it flew at the same speed as the light bow, they'd have a LOT more momentum. So it still comes down choices we make and how we use the KE.....O.L.

[O.L. Adcock]

A couple other ways to grasp this KE thing..It's the "time" factor that throws folks...Which gear in your truck will do the most work with the least horsepower? Low gear   But it won't do it very fast (time). If I want to do the same work faster I have to have more horsepower. We don't have more horsepower, our bows have fixed horsepower.

A decent 50# bow will put 38-40ft/lbs KE into an arrow and the "work" we are trying to do is push a broadhead through something. We've all heard that 1ft/lb is the energy needed to move 1 pound 1 foot in 1 second...So 40ft/lbs would be 40 pounds, 1 foot, in 1 second...Shoot a 40# block and see if it will move it 1 foot...Nope...Not even close...Because we're trying to do it too fast. 40ft/lbs 1 foot in 1 second...How much "work" can that much energy move in .5 seconds? (twice as fast)...Answer.... 10 pounds...Moving 10 pounds 1 foot in .5 seconds is 40ft/lbs. By trying to do the work twice as fast we've cut the total amount of work it'll do to 1/4...How about .25 seconds? 2.5# From any given bow, every time you double it's speed by lowering arrow weight you are reducing the work it can do by 400%! But that works in reverse also. Scary stuff!   ....O.L.