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Does FOC change the kinetic energy?

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Fatguyinatree

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Discussion starter · #1 ·
Hi everyone!

I'm short and stubby with an old injury. My draw length is 27" and it's at 60lbs. It's rated 300 ibo but I guess it's more like 275.
I found an online speed calculator and I'm trying to wrap my head around FOC and kinetic energy. Doesn't help that I'm slow. But after plugging in data into this calculator I was wondering if the FOC would change the kinetic energy. Am I wrong for thinking this? I recently went with 125grain field points to increase the weight and FOC for hunting. It shoots target bags and 3ds fine. Now I'm not sure if my bow is to slow for them to hunt with.
www.omnicalculator.com

Arrow Speed Calculator

Arrow speed calculator finds the real speed of an arrow for a bow with custom parameters.
www.omnicalculator.com www.omnicalculator.com

Thanks for any insight!
 
#2 ·
Speedwise, you are just fine bud. It wasn't too long ago that 250 fps was considered blazing fast and I promise you those bows killed just fine. Now the other part, lots of tests have been done and while FOC doesn't necessarily increase kinetic energy, it can help with penetration.
 
#5 ·
The added weight changes the momentum. No matter what combination I run of arrow weights, at my setup my KE will always be from a low of 55 to a high of 62 or so. My typical arrow will be 425 or so, and about 260 fps, but I shoot 450 or so some at 230 -250 fps. And I will shoot a 540 grain or so sometimes at around 220 fps. The heaviest arrow, the higher momentum arrow ( regardless of foc) has the most punch. The main thing is it makes ranging more important, you have to get your yardage right , because of the additional arch in your arrow. But other than that, I have punched through both shoulders of hogs with the heaviest arrow a little better I think, I can notice just a little more punch. Its the density, mass of the heavier shaft and concentration of energy behind the broadhead. I use different weights, I don't always use the heaviest arrow. But my analysis of this whole thing after just watching what happens, its the density, mass, concentration of energy in that arrow,momentum despite the change in velocity. I might shoot something with 385 grain arrow tomorrow. But after using a lot of different weight arrows, I have no doubt about weight, mass , density, momentum, and what it does. There is just a diminishing return for all of us at some point. And broad head design matters.
 
#6 ·
Longbow_7 said:
No.

There are 2 variables that go into kinetic energy. Mass and velocity.
Click to expand...
This is correct. You can think of your bow as a kinetic energy machine. It stores the same amount of energy every time you draw it.

Increasing FOC does not change the amount of energy the bow will transfer to the arrow. However, heavier arrows will absorb energy more efficiently than a lighter arrow assuming the spine is stiff enough. Shooting a heavy arrow with a lot of FOC may actually decrease your KE slightly if the arrow flexes too much during the power stroke. It won't be much but it does exist.

As far as I am concerned the primary benefit to increasing FOC is stability in flight. Higher FOC equates to the vanes having more leverage with which to stabilize and correct flight.

Ashby says that EFOC (19%-25%) will show a significant increased in penetrating ability. Whether that is accurate I don't know for sure.

I think 250 fps is sufficient for hunting. I am currently shooting 270 fps for my hunting arrows. Although I do have some heavier stuff that runs around 255 fps. For hunting inside 40 yards I would have no problem shooting any of them.

I say if it is shooting well for you then run with it, no need to change. But if you want to tinker and try new stuff, do it.
 
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#10 ·
One way to think of it that kenitic energy is only affeted by mass and velocity. The KE equation cuts the mass in half, so its affect is not near as much as velocity which is squared.

1/2 m* velocity ^2 = KE.

Adding mass only slightly affects KE, but adding or losing velocity greatly affects KE.

Momentum is mass times velocity, so each play an equivalent role
 
#12 ·
If you went from 100 to 125 grain heads you probably only lost 8-10 fps and the KE probably didn't change much at all...increasing the FOC will probably give you a little better flight with broad-heads...just make sure your still in tune with the extra weight and then go forth and slay critters....
 
#13 ·
If your bow is tuned, a nice sharp broadhead is probably more important than FOC or having a "heavy" arrow. I would avoid anything ashby or the fairy says in regard to compound bow hunting. I would get a nice arrow build that tuned well in my bow, gave me enough speed so I wasn't lobbing arrows like hand grenades, and get a nice sharp broadhead on the end of it.
 
#15 ·
I don't know if anyone said this yet, but if two arrows weigh the same and one has low and one has high foc, they will have the same KE or momentum. I believe I have to be right on this.:)
 
#16 ·
Mallardbreath said:
I don't know if anyone said this yet, but if two arrows weigh the same and one has low and one has high foc, they will have the same KE or momentum. I believe I have to be right on this.:)
Click to expand...
You are correct
 
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#17 ·
Fatguyinatree said:
Hi everyone!

I'm short and stubby with an old injury. My draw length is 27" and it's at 60lbs. It's rated 300 ibo but I guess it's more like 275.
I found an online speed calculator and I'm trying to wrap my head around FOC and kinetic energy. Doesn't help that I'm slow. But after plugging in data into this calculator I was wondering if the FOC would change the kinetic energy. Am I wrong for thinking this? I recently went with 125grain field points to increase the weight and FOC for hunting. It shoots target bags and 3ds fine. Now I'm not sure if my bow is to slow for them to hunt with.
www.omnicalculator.com

Arrow Speed Calculator

Arrow speed calculator finds the real speed of an arrow for a bow with custom parameters.
www.omnicalculator.com www.omnicalculator.com

Thanks for any insight!
Click to expand...
No, well depends to what what degree you increase or decrease the FOC, only things changing KE are speed and weight , balance doesn’t matter, it does affect arrow flex in flight, a lot of flexing would affect accuracy, AND CAUSE HELICAL FLIGHT, linear with arc in one plane is desired, fixed blades planing also I would think, which is why high speed bows are shot with mechanicals as many archers are in a trend of heavy arrows which they create by adding heavy points and inserts IMO. I don’t agree with that , I like to l look at the Curve of the KE within the limits of your bow and draw weight, spine of arrow, law of diminishing returns always applies, at a point a heavier point and inserts with a high FOC will cause drop in KE and effective range, likewise a lack of FOC froma very light point causes drop in KE , most archers are in the optimum zone, going by spine charts as a starting point and make small adjustments from there more or less or else they have erratic undesirable arrow flight, poor penetration , etc.
 
#20 ·
sticknstring007 said:
If your bow is tuned, a nice sharp broadhead is probably more important than FOC or having a "heavy" arrow. I would avoid anything ashby or the fairy says in regard to compound bow hunting. I would get a nice arrow build that tuned well in my bow, gave me enough speed so I wasn't lobbing arrows like hand grenades, and get a nice sharp broadhead on the end of it.
Click to expand...
Had a Hoyt said:
I got a complete pass through on a bull moose at 57 yards with a 60 pound bow pushing a 400 grain arrow (28" draw)
Click to expand...
awesome
 
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