Let's discuss.....
#12
Join Date: Feb 2003
Location: Hamilton Square NJ USA
Posts: 557
RE: Let's discuss.....
It's just basic physics, momentum and KE start decreasing the second the arrow leaves the bow. There's no way an arrow can gain speed after leaving the bow, and any number of variables will cause it to lose speed.
Well, maybe shooting straight down it would pick up speed.
Well, maybe shooting straight down it would pick up speed.
#13
Giant Nontypical
Join Date: Feb 2003
Posts: 9,175
RE: Let's discuss.....
I'm awake. Just formulating my response.[8D]
About the guy getting hit in the head, he's still alive because nobody has ever shot an arrow that was completely stablized as it left the bow. I bet that arrow doubled up as if flexed when hitting his skull.[:-]
As soon as the arrow leaves it's power source, wind resistance starts slowing the arrow down, draining off it's speed, energy and momentum (though the higher the momentum, the more speed and energy the arrow retains). The arrow doesn't have all it's energy and momentum established in the same line until it has stabilized it's flight.
About the guy getting hit in the head, he's still alive because nobody has ever shot an arrow that was completely stablized as it left the bow. I bet that arrow doubled up as if flexed when hitting his skull.[:-]
As soon as the arrow leaves it's power source, wind resistance starts slowing the arrow down, draining off it's speed, energy and momentum (though the higher the momentum, the more speed and energy the arrow retains). The arrow doesn't have all it's energy and momentum established in the same line until it has stabilized it's flight.
#14
RE: Let's discuss.....
One thing I've noticed with ballistics calculators. KE changes very little with lighter arrows going faster. Momentum is better retained with heavier arrows, with similar KE. I'm not so sure penetration would be much different at close range, but farther out the arrow with more momentum should penetrate more.
If I remember correctly, the bow was not fully drawn when the guy was shot in the head. It may also be that the bow didn't go through the full power stroke because he was hit before the arrow left the string. Either way, that must hurt like crazy. [:@][]
If I remember correctly, the bow was not fully drawn when the guy was shot in the head. It may also be that the bow didn't go through the full power stroke because he was hit before the arrow left the string. Either way, that must hurt like crazy. [:@][]
#15
Join Date: Dec 2003
Location: Kansas
Posts: 316
RE: Let's discuss.....
I will go ahead and post up, from an engineering standpoint. I am an engineer, so I am somewhat qualified.
THe two formulas M=m*V and KE=m*V^2, or KE=m*V*V. Both formulas have V or velocity/speed in them. An arrows highest speed is the second it leaves the bow. From that point forward, it is losing speed, just like a bullet. Your highest KE and M are at that first instant. Where things get dicey is the point of impact. If that arrow is flopping like a fish, the ability to transfer that KE or M in a straight line is reduced, as a function of the amount of deflection from straight. Basically you decrease efficiency at which that arrow can continue in a straight line. There is a finite amount of energy available to a projectile. If the projectile if flying straight, more of that available energy is spent continuing the path forward. The more side to side, the more energy you lose. It is the opposite of mechanical advantage. There is no more engergy being input into the projectile, so it is all losses. The fewer the losses, the more energy or momentum is available to continue in the straight line and overcome the resistance presented by penetration.
Hope this made sense, or was at least as clear as mud. I have not proof read yet, as I was in a bit of a hurry, but I can add more later.
JMAC
THe two formulas M=m*V and KE=m*V^2, or KE=m*V*V. Both formulas have V or velocity/speed in them. An arrows highest speed is the second it leaves the bow. From that point forward, it is losing speed, just like a bullet. Your highest KE and M are at that first instant. Where things get dicey is the point of impact. If that arrow is flopping like a fish, the ability to transfer that KE or M in a straight line is reduced, as a function of the amount of deflection from straight. Basically you decrease efficiency at which that arrow can continue in a straight line. There is a finite amount of energy available to a projectile. If the projectile if flying straight, more of that available energy is spent continuing the path forward. The more side to side, the more energy you lose. It is the opposite of mechanical advantage. There is no more engergy being input into the projectile, so it is all losses. The fewer the losses, the more energy or momentum is available to continue in the straight line and overcome the resistance presented by penetration.
Hope this made sense, or was at least as clear as mud. I have not proof read yet, as I was in a bit of a hurry, but I can add more later.
JMAC
#16
Join Date: Feb 2004
Location: Wyoming
Posts: 287
RE: Let's discuss.....
The article you spoke about and the accomanying pictures was gross the guy was just lucky man.
As to your response, a question i would have is: Just how much does an arrow resist being pushed off the string (an object at rest tends to stay at rest), and how much stored energy does the flexing of the arrow release before it actually leaves the string? As an example ; If the arrow only moves 12 inches before it makes contact with an object at rest how much KE is expelled before it gets there. At three feet? at 6 feet? (as long as we are measuring in yards). If a 70# bow has a 65% letoff and the arrow has only moved 6 inches before is stikes an object, is the full force (Potential) of the arrows energy been achieved?
As to your response, a question i would have is: Just how much does an arrow resist being pushed off the string (an object at rest tends to stay at rest), and how much stored energy does the flexing of the arrow release before it actually leaves the string? As an example ; If the arrow only moves 12 inches before it makes contact with an object at rest how much KE is expelled before it gets there. At three feet? at 6 feet? (as long as we are measuring in yards). If a 70# bow has a 65% letoff and the arrow has only moved 6 inches before is stikes an object, is the full force (Potential) of the arrows energy been achieved?
#17
Nontypical Buck
Join Date: Feb 2003
Location: Wisconsin
Posts: 3,903
RE: Let's discuss.....
Pertaining to the article , the reason it didn't penetrate further was because the guy stood up just inches in front of his brother when he shot. Luckily for him he was so close that the bow didn't complete it's power stroke.
Good post though! I think about this stuff alot too! I dont really have anything to add that hasn't been said already.
Good post though! I think about this stuff alot too! I dont really have anything to add that hasn't been said already.
#18
Nontypical Buck
Join Date: Feb 2003
Location: Wisconsin
Posts: 3,903
RE: Let's discuss.....
To add more confusion and headaches.
Anyone else experience this besides me?
I was shooting a 3d target last year with some alluminums out of my Hoyt Ultratec. I chrono'd them at 273fps. I started shooting the Mckenzie target (brand new) from 20 yds. I then backed up to 30 yds. The penetration at 30 yds was a good couple inches deeper than 20 yds. Now I'm no rocket scientist here , but by my experience I have to assume that with a heavier arrow momentum will actually increase down range in certain instances.
Anyone else experience this besides me?
I was shooting a 3d target last year with some alluminums out of my Hoyt Ultratec. I chrono'd them at 273fps. I started shooting the Mckenzie target (brand new) from 20 yds. I then backed up to 30 yds. The penetration at 30 yds was a good couple inches deeper than 20 yds. Now I'm no rocket scientist here , but by my experience I have to assume that with a heavier arrow momentum will actually increase down range in certain instances.
#19
RE: Let's discuss.....
I have to assume that with a heavier arrow momentum will actually increase down range in certain instances.
My guess on your better penetration is that the arrows were stabilized better at the longer distance.
#20
Giant Nontypical
Join Date: Feb 2003
Posts: 9,175
RE: Let's discuss.....
Maybe it's possible for an arrow shot at an extreme downhill angle to increase it's speed, energy and momentum, IF gravity can give it enough of a boost to overcome the wind resistance. Possible?!? On a level shot, wind resistance is going to guarantee a loss in speed, energy and momentum. But the heavier arrow will definitely retain what it leaves the bow with better than the light arrow.
Two arrows from the same bow, one maybe 350 grains and the other, say 600 grains. The light arrow will have greater speed, only slightly less energy and a good bit less momentum. The heavy arrow will have a good bit less speed, slightly more energy and greater momentum. The sliding scale and trade-off thing I was talking about on the other thread. You gotta give up something to get something else. Increased speed and better trajectory vs increased momentum and better penetration.
The light arrow has less momentum working for it, so it uses up a higher percentage of it's speed and energy just getting to the target than the heavy arrow. The light arrow doesn't even penetrate AIR as well as the heavy arrow. An animal's ribcage?? Well.... I believe flesh and bone is more dense and resistant than air.
You CAN jack up the speed enough to increase momentum to equal the heavy arrow, BUT... The heavy arrow would have to be shot from a 60 pound, round wheel bow vs the light arrow from an extremely high poundage cam bow.
People like to talk energy because it's easier to understand 60 ft lbs vs 80 ft lbs. 6578 pound/seconds... What the heck is THAT? Momentum in that form shows momentum's relationship to how energy is expended over time but it is hard to understand in that form.
I like the old formula I used to see all the time in the gun magazines. I think it's the Hatcher penetration index, but it's been years since I was into handguns and I don't remember too well. Anyway, it's projectile weight in grains times speed divided by 10,000.
A 350 grain arrow at 300 fps and 70 ft lbs will have a penetration index of 10.5.
A 600 grain arrow at 230 fps and 70 ft lbs will have a penetration index of 13.8.
To get the 350 grain arrow up to 13.8, you have to drive that suckah at 394 fps for 120 ft lbs! Will an arrow with 120 ft lbs penetrate better than an arrow with 70 ft lbs? I would HOPE so! But which would you rather shoot on a daily basis?
13.8 vs 10.5 doesn't sound like a great deal, but look at the percentages. Momentum is nearly 40% higher at a 24% sacrifice in speed. Gain in penetration potential vs loss in trajectory.
The ballistic table at Jacksons seems to be pretty accurate at predicting downrange velocity loss. You can plug your numbers in and figure the index at different yardages. It will steadily decrease at each distance, but the heavy arrow will show higher retention of what speed it does have, along with energy.
So, I guess that's the long version of saying I agree with Frank. Your arrow had to have been wibbly wobbly at 20 yards but finally stabilized when it got to 30 for there to have been better penetration at 30. Or you shot a soft spot in the target at 30.
Now that I've posted, I'll go get a cup of coffee and see if I can understand what I just wrote. [:-]
Two arrows from the same bow, one maybe 350 grains and the other, say 600 grains. The light arrow will have greater speed, only slightly less energy and a good bit less momentum. The heavy arrow will have a good bit less speed, slightly more energy and greater momentum. The sliding scale and trade-off thing I was talking about on the other thread. You gotta give up something to get something else. Increased speed and better trajectory vs increased momentum and better penetration.
The light arrow has less momentum working for it, so it uses up a higher percentage of it's speed and energy just getting to the target than the heavy arrow. The light arrow doesn't even penetrate AIR as well as the heavy arrow. An animal's ribcage?? Well.... I believe flesh and bone is more dense and resistant than air.
You CAN jack up the speed enough to increase momentum to equal the heavy arrow, BUT... The heavy arrow would have to be shot from a 60 pound, round wheel bow vs the light arrow from an extremely high poundage cam bow.
People like to talk energy because it's easier to understand 60 ft lbs vs 80 ft lbs. 6578 pound/seconds... What the heck is THAT? Momentum in that form shows momentum's relationship to how energy is expended over time but it is hard to understand in that form.
I like the old formula I used to see all the time in the gun magazines. I think it's the Hatcher penetration index, but it's been years since I was into handguns and I don't remember too well. Anyway, it's projectile weight in grains times speed divided by 10,000.
A 350 grain arrow at 300 fps and 70 ft lbs will have a penetration index of 10.5.
A 600 grain arrow at 230 fps and 70 ft lbs will have a penetration index of 13.8.
To get the 350 grain arrow up to 13.8, you have to drive that suckah at 394 fps for 120 ft lbs! Will an arrow with 120 ft lbs penetrate better than an arrow with 70 ft lbs? I would HOPE so! But which would you rather shoot on a daily basis?
13.8 vs 10.5 doesn't sound like a great deal, but look at the percentages. Momentum is nearly 40% higher at a 24% sacrifice in speed. Gain in penetration potential vs loss in trajectory.
The ballistic table at Jacksons seems to be pretty accurate at predicting downrange velocity loss. You can plug your numbers in and figure the index at different yardages. It will steadily decrease at each distance, but the heavy arrow will show higher retention of what speed it does have, along with energy.
So, I guess that's the long version of saying I agree with Frank. Your arrow had to have been wibbly wobbly at 20 yards but finally stabilized when it got to 30 for there to have been better penetration at 30. Or you shot a soft spot in the target at 30.
Now that I've posted, I'll go get a cup of coffee and see if I can understand what I just wrote. [:-]