kenetic energy and speed

[jkb]

I know how to figure K E but is there a formula for figuring the speed I would drop by going a little heavier arrow.???????How much K E do I need to put arrow threw deer at 40 yards????

[BGfisher]

If you can shoot the bow after it is tuned well, and shoot a normal configuration of any modern compound bow/arrow setup with the bow peaking about 50# then you have enough for deer. Regardless of the Kinetic Energy. Don't you know???? Kinetic energy kills nothing. Well placed, very sharp braodheads are what does the killing.

[Screamingeagle]

And momentum = penetration.

[PABowhntr]

jkb,

Steve Jackson has a website with a variety of archery related "calculators" on there. That might help. www.bowjackson.com Also, I believe the general rule of thumb is 1 fps lost for every 3-4 grains of arrow weight added.

Hope this helps.

[Gundigest]

It only takes about 40 ft-lbs of kenetic energy for a pass threw on a deer, however shot placement is more important. The Gold Tip website has some calculations on it.

[98Redline]

One thing to remember when figuring out the change in arrow speed vs. a change in arrow weight......The KE developed is a function of the bow more than a function of the arrow. In mathmatical terms, the KE developed is the integrated area under the draw force curve for the bow, minus the bow inefficencies (friction, noise, etc....).

Given a bow with the same draw length and weight, the KE developed for a super light arrow will be nearly the same for a super heavy arrow. The light arrow will just be a ton faster.
There are some small gains for using a heavy arrow as the bow efficency tends to go up which will yield you slightly more KE, but this figure is normally < 1ft-lb.

[Sylvan]

Given a bow with the same draw length and weight, the KE developed for a super light arrow will be nearly the same for a super heavy arrow. The light arrow will just be a ton faster.
There are some small gains for using a heavy arrow as the bow efficency tends to go up which will yield you slightly more KE, but this figure is normally < 1ft-lb.

KE = m/2 x (SE / (m + mv))**1/2

where:
SE = stored energy
KE = kinetic energy
m = mass of arrow
mv = virtual mass of the bow

Clearly, KE is a function of the mass of the arrow. If we use an example of a bow storing 90 ft/lbs that throws a 350 grain arrow at 300 ft/sec which is 70 ft/lbs and we assume virtual mass to be 100 grains then that same bow will propel a 600 grain arrow at 240.5 ft/sec which is 77.1 ft/lbs. This is a 7.1 ft/lb or 10.2% increase in KE. In my opinion this is a very significant increase. In terms of momentum the change is from .47 to .64 slug ft/sec or a 37.4% increase. Certainly, super light arrows will travel alot faster but its also true there is a price to be paid.

[SA Techie]

One other thing, mechanicals (If ure shooting them) will need a bit more KE than fixed blades. Spitfires and the like open at around 55# or so.