silentassassin

Kinetic Energy and Momentum. I am not meaning this to get into an argument but rather to get some input from some of those with engineering backgrounds and various other expertise. First, let me start by asking does an arrow gain momentum as it travels down the course? For example, if you placed a target at 3 feet, would it penetrate deeper (have more momentum) than it would if the target were placed 40 feet? If so, would the arrow be gaining momentum as it traveled? Also, if this is the case and momentum increases and KE decreases and you actually get better penetration with the same arrow at 40 feet, with less KE than you had at 3 feet, wouldn't that be a strong indicator of which was the better measure for penetration? Just some of my rambling thoughts, I hope they make sense. I have always leaned toward KE as the best measure but I don't ever remember this mentioned in those debates, so I thought I would ask for opinions. This question was spurred from a post in the offseason forum, which shows a man with a broadhead embedded in his skull. I remebered reading the article when this first happed where someone stated that the guy was lucky that he was so close the arrow, the arrow didn't have time to game momentum, otherwise it would have penetrated further and killed him. I thought I would bring that statement to the experts for their perspective opinions on the subject.

Rack-attack

Come on!!!!! I am bored to death....lets get nasty

Momentum, Kenetic Energy and speed decrease as soon as the arrow leaves the bow.

A heavier, higher momentum arrow will loose less of a % of its energy as it travels towards a target than a lighter faster arrow.

But unless that nock has some rocket boosters on it - its all downhill once it leaves the string

jsasker

True,but will the arrow be stabilized enough at 3 feet to penetrate better than at a farther distance?

Rangeball

I would suspect it would have a lot to due with the tune of the bow, how well the spine match was and what kind of fletching was being used to stabilize. FOBs and Turbo nocks are reported to stabilize very quick, as are NAP's new vanes, then probably feathers then vanes, generally.

However, if I was shooting at something I was looking to maximally penetrate, I'd probably release before it got within 3' of me...

Rack-attack

If you were to consistantly experience better penetration at 20 yds than at 3 feet - then yes I would say that arrow stabilization is the major player inhibiting the 3 foot shot - not momentum

PABowhntr

I personally believe that both KE and momentum play a role when attempting to determine how far a specific arrow will penetrate at various distances. However it is difficult to really do a true comparison because when we change arrow weights and speeds to cause differences in KE and momentum then we also potentially change other variables as well....shaft diameter and construction, Front of center balance, spine, etc...

I believe the "stabilization after release" issue is probably the reason that the arrow did not cause more damage in the case you mentioned.

Trushot_archer

Both KE and momentum calculations require speed as a factor. Speed decreases downrange...as does KE and momentum.

Momentum has to do with inertia. An object at rest or in motion will sty at rest or in motion until energy is exerted upon it. The energy exerted on the arrow is gravity and wind resistance. The greater the mass of the projectile the more inertia it carries (all else being equal) and the more force it takes to negate the energy it carries.

I think.

Hell, I'm just a cook

silentassassin

I should have clarified that a little more. For the point of this discussion let's assume all else is equal. In both situations the arrow is stable when entering into the target and the bow is tuned perfectly.

Rack-attack

That statement is just wrong.

All else being eqaual the arrow at 3 feet has more speed, KE, and momentum.

silentassassin

I'm sure you're right but I wonder if there have been any tests done or if there is any statistical data to confirm that.