arrow physics 2

[Rob DiStefano]

Originally posted by Zradix:
Thanks for all the help guys. Yeah I have to admit I'm a little worried about overkill. Don't need to use an elephant gun on a mouse. I'm wondering if the 10gn/# will pass thru just like the 13 on whitetails.

i think you need to stop thinking about this, yer gonna hurt yerself with all these thoughts.

10ggp or 13gpp? - take yer pick, go out and make meat.

[Jim now in Kentucky]

Just for the record, drag is proportional to the CUBE of the velocity, not the square of velocity.

And while we're at it, force = mass X acceleration--or deceleration.

Both arrows will lose the same amount of energy to drag--the heavier one will lose less velocity, but had less to begin with.

If both arrows arrive at the target with the same energy, the energy lost to the target will be equal.

How many of you pontificators actually studied physics?

[Zradix]

That's my problem! How much energy will each arrow have at the target? this is fun!

[Richie Nell]

The lighter arrow will have less momentum or force downrange than the heavier arrow. Period

Momentum is penetration. Another period.

[oxnam]

I know the original question was that the arrows are going the same fps.  But that can only happen if they are shot off different bows or the same bow drawn to different lengths.  It gets a lot more complicated if you consider the given arrow weights with the appropriate different fps (shot from same bow).  

I shoot 3D with my father who uses a compound.  Light arrows and decent fps at aprox 280.  I shoot slower heavier arrows, but I NEVER get better penetration.  Doesn't matter if the target is at 10 or 50 yards, his penetrates better. I am not sure how to run the math but his fast and light beats my slow and heavy.

[Jim now in Kentucky]

NO. The original question stated that the arrows had the same energy--they were going DIFFERENT speeds.

Sir Nell, What is your training in physics?

[Bill Carlsen]

Here is my take on it. Both arrows you describe are more than adequate. You should shoot the arrow that shoots the straightest and the best way I know how to determine this is to bare shaft and then see what happens when you put on your choice of broadheads. If both arrows shoot equally straight my preference would be the heavier arrow or the one with the highest FOC. Higher FOC just make penetration less of a problem, even with lighter arrows.

[Hud]

Personally, I would select an arrow that flies the best, and groups the best all things being equal (which they are not). Because your arrow speed is 135 fps vs 150 fps, I agree with Mike and probably would go with the later. The majority say weight, but you need to be able to hit what your aiming at regardless of the distance. If 20 yds is your effective range, shoot them then decide.

You did not mention the bow weight, which is important in the discussion, particularly if your shooting a relatively light weight (40-45, 45-50 lbs) with that weight arrow. What arrow material, wood, alu, graphite. What is the FOC? If your shooting a relatively light bow with a heavy arrow, you might consider a lighter arrow with with a higher FOC. Again, reference was made to Dr. Ashby's report. He recommends an FOC as high as possible, 19-30%, and it is easy to confuse a heavy arrow with being the same, when it is not. You may find a lighter arrow with a high FOC that shoots outstanding and penetrates better with a two blade with a 3:1 ratio, eg. Grizzly.

[Richie Nell]

Sir Jim,
Nothing special like yourself.  Just a biology and science major and common sense.  

Now let us all know of your credentials.

[Hud]

If penetration is the concern, the higher FOC with a broadhead with a ferrule the same diameter of the shaft, is better than a small ferrule on a large shaft. Small diameter shaft is going to have less friction than a large diameter shaft, all things being equal. (anyone interested in some 2315 Eastons?)

As for weight to bow draw weight, Fred Bear used a 610-625 gr. arrow with a 65 lb bow for years, which is 9-10 grains/draw wt., and he wasn't too concerned about knocking down.

[FlintRiverKen]

I am considering going from POC to Ash to get better penetration with the lighter bow I'm shooting now. The example in this thread has the Ash about 26% heavier. I wonder if that is typical.

Hud, so I could maybe keep the POC shafts I have and just increase my FOC. Looks like I could do that keeping my same heads with the new tool at 3R you add a nail footing- anybody have experience with this one?
----------------------
The new internal point weight and footing jig allows you to easily add weight and strength to your wooden arrows and shafts. Simply use the supplied drill bit with your variable speed hand drill to create a precisely aligned internal cavity at the point end of the shaft. Insert a 1/8" rod or nail of your choosing, and then affix the point as normal. Available for 11/32" or 23/64" shaft sizes, 9/64" drill bit included. This jig is specifically designed to accomodate the slight diameter variations typical of wood shafting. However, for best results use the jig size that corresponds to your shafting size. Comes with instructions.
Easy to use
Instructions included
Great weight ot Increase FOC on wood arrows

[Richie Nell]

If a plastic golf ball and a real golf ball were propelled into a glass widow, why would the plastic ball require much more speed than the real golf ball to break the widow?

[Jim now in Kentucky]

A year of physics--some time after Newton put forth his formulas.

Common sense, and biological science didn't get anybody off the ground, though they tried.

If the energy of two dimensionally identical arrows is equal at impact, penetration will be equal. The aspects of momentum and inertia are just different representations of energy.

[Steve B.]

If the bow was held the same for each arrow then the heavier arrow would hit in the dirt in front of the target and ruin this discussion.
Since the bow would have to be tilted higher for the heavier arrow to hit the target then gravity would have more time to affect the heavier arrow as it arcs toward the target.  Since the angle of attack is greater for the heavier arrow it picks up more speed and so hits the target with more force.
I have no physics training but I know if you drop two objects from a skyscraper they hit at the same time.

[Richie Nell]

"Common sense, and biological science didn't get anybody off the ground, though they tried."

Thanks for the confidence booster.  Don't tell my boss...O wait...I am the boss.

"If the energy of two dimensionally identical arrows is equal at impact, penetration will be equal. The aspects of momentum and inertia are just different representations of energy."

They may begin with the same energy but they are not gonna end the same.  That is exactly why the heavier arrow DOES penetrate better.  Downrange it simply is not too fond of stopping as quick as the lighter arrow.  

Is that not what you have found to be true?

[Rob DiStefano]

Originally posted by FlintRiverKen:
I am considering going from POC to Ash to get better penetration with the lighter bow I'm shooting now. The example in this thread has the Ash about 26% heavier. I wonder if that is typical.

Hud, so I could maybe keep the POC shafts I have and just increase my FOC. Looks like I could do that keeping my same heads with the new tool at 3R you add a nail footing- anybody have experience with this one?
----------------------
The new internal point weight and footing jig allows you to easily add weight and strength to your wooden arrows and shafts. Simply use the supplied drill bit with your variable speed hand drill to create a precisely aligned internal cavity at the point end of the shaft. Insert a 1/8" rod or nail of your choosing, and then affix the point as normal. Available for 11/32" or 23/64" shaft sizes, 9/64" drill bit included. This jig is specifically designed to accomodate the slight diameter variations typical of wood shafting. However, for best results use the jig size that corresponds to your shafting size. Comes with instructions.
Easy to use
Instructions included
Great weight ot Increase FOC on wood arrows

that's the braveheart archery footing weight jig - love it!  adds arrow gpp weight, foc forward balance and stiffens a wood shaft's critical area behind the point.

2 thumbs up for the braveheart foot weight jig!

       

[Zradix]

Only if the skyscraper is in a vacuum chamber. or are identical in drag

[Mike Most]

What an excellent topic, while I follow most of it,  I wish I had paid more attention in math and physics classes. I may well try the new footing weight jig mentioned above.


Mike

[Jim now in Kentucky]

No Richie, as a matter of fact, if a lighter arrow has the same energy as a heavier arrow, that means the lighter arrow is going faster.

They would lose the same amount of energy in a substance of uniform consistency--and they would stop at the same point.

The difficulty in understanding this is that we never have a controlled situation and enough instances to see a clear picture of the results.

Most of the time, a bow will put more of its available energy into a heavier arrow--which will indeed penetrate farther than a similar, but lighter, arrow from the same bow, because the lighter arrow carries less energy away from the bow. The energy not put into a lighter arrow dissipates as hand shock, string stretch, vibration and so on.

Jim

[Zradix]

Jim... What are the tubes in your profile?