RE: What is the best way to get kinetic energy II
 

I agree with your explination of momentum and am not arguing the point.

But when is enough enough?

Are you saying that 400 grains is to light and won't carry enough momentum for some Ohio whitetails?

I really don't think so.

RE: What is the best way to get kinetic energy II
 

Syl you put that into words much better than I could. Right on:)

RE: What is the best way to get kinetic energy II
 

sylvan, actual momentum is .7247097 at slug-feet/second.
buckeye, your k.e. is great , your momentum is great, and you should have no problem shooting though any game animals. if you us a razor sharp broadhead, and hit the vitals!:D
as i said before no matter what all those tough guys have for #, K.E. and speed, the speed of sound will always be faster, and a whitetails 1110 fps will always be faster[X(] so just shoot a quiet bow with accuracy. and u will never have tag soup![:'(]

RE: What is the best way to get kinetic energy II
 

That is simply not correct. Any book on mechanics will tell you that KE is the indicator of the depth of penetration while momentum determines if penetration will take place or not. KE is defined as the integral of force over distance. Momentum is defined as the integral of force over time. The example you use though demonstrates approximately equal amounts of ke but significant difference in momentum is so extreme it is not analogous to any real hunting scenario. A sharp broadhead shot by even a significanlty below averge strenghth man WILL penetrate flesh. The best indicator of how far it penetrates is KE.

Anyway like I've said before this is a silly argument. In archery, everything you do to increase momentum also increases KE and everything you can do to increase KE also increases momentum. The go together they are not opposites.

For those who think momentum is all important, please put a number on it. Please tell us in slug ft/sec what you think the minimum adequate amount is. Once you decide that start generating examples of arrow weight and velocity that give you that minimum momentum and you will find that you will ALSO be in the neighborhood of acceptable minimum KE.

RE: What is the best way to get kinetic energy II
 

manboy, O.K. lets play trivial numbers pursuit. You obviously didn't get this number by (550/225120) times 297 like I said in the original post or you would have got .7256130 which is different from your number by 0.0009033 No thats a huge difference why its a little more than 1/10 of 1% difference, I see why you broght it up. Now how can we account for it? You either ran a little program or you calculated it yourself but either way gravity comes in to it doesn't it? So what did you use for g. I used 32.16 ft/sec/sec. Did you use a different value? I bet you did. Either that or you just ran a little program to give you an answer and you have no clue as to why there is a difference.

RE: What is the best way to get kinetic energy II
 

sylvan, here is a example for you
K.E. determines how HARD an object hits. not how far it penetrates.
momentum is how hard the object is to stop.
SECTIONAL DENSITY = how effectively it penetrates.
5 gallon bucket full of sand. shoot it with a .357 mag. and an 500 grain arrow at 165fps. and thow a baseball 5.12 ounces at 95 mph.
the .357 bullet has a k.e. of 583 ft-lbs, it also has a momentum of .80
the arrow has a k.e. of 29ft-lbs and a momentum of .37
the baseball has a k.e. of 87ft-lbs and a momentum of 1.31
WHAT ONE SHOOTS THOUGH THE BUCKET? the ARROW
p.s.i. arrow= .508, bullet=.140, and the tough guy baseball=.039 THANKS:eek:

RE: What is the best way to get kinetic energy II
 

SORRY I USED 32.2 GRAVITY[:@]

RE: What is the best way to get kinetic energy II
 

KE is simply the energy that motion imparts to an object (mass). It's a quantitive value. It could be going straight or going around in circles and still have the same amount of energy. Momentum is a vector. It is what determines what direction that energy is directed. It determines how that energy will be expended.

Remember this law of physics? An object in motion tends to stay in motion until acted upon by a force. The greater the momentum, the greater the opposite force needs to be to stop it. The less momentum an object has, the easier it is to stop.

Kinetic energy is proportional to the square of it's speed. Wind resistance for subsonic projectiles is proportional to the cube of it's speed. Wind resistance or drag is an opposite force acting to stop an arrow. Out of a given bow, a lighter, faster projectile is carrying less kinetic energy at a greater speed, with less momentum and having to fight increased wind resistance. It uses up a greater proportion of it's energy just cutting through air than the heavier, slower arrow does.

Simple test of the concept. Stick your hand out the car window at 40 miles an hour then speed up to 70 and do it again. A very dramatic increase in wind resistance, isn't there.

The heavier, slower arrow starts out with more energy. It has more momentum and less wind resistance. That's why it gets out to longer distances retaining a higher percentage of it's energy. And it started out with more energy than the light arrow did, in the first place.

Simple, isn't it.

Again, if you've got energy to burn, then you've also got a healthy amount of momentum and you might as well rocket your arrows along, if you're after thin skinned critters like deer. A 350 gn arrow at 300 fps gives exactly the same momentum as a 700 grain arrow at 150 fps and, at the same time, carries twice the heavy arrow's energy. Both arrows will blow through a deer at 20 yards. So, how can anyone say KE is THE indicator of penetration? Easy answer, it's not.

I agree that, to guys who are shooting high poundage, hard cam, efficient bows, this is a silly argument. But not everyone is shooting that kind of bow. There are people who have to use bows on the low end of legal hunting weight. There are people using older, less efficient bows. Traditional and primitive bows. Low poundage/low efficiency bows do not generate gobs of excess energy. For those people, this is definitely not a silly argument.

It gets dangerous when the KE/speed crowd talks about mandating minimum KE values because it's a false premise that would needlessly put a good number of legal, ethical bowhunters out of bow season.

RE: What is the best way to get kinetic energy II
 

I would reverse what you are saying here.

Comparing bullets and arrows is IMO a meaningless exercise. Arrows penetrate because they are very very sharp. Comparitively bullets though dull penetrate because the carry much more energy. But seeing that we are just playing around, lets change the object to a cinder block. Now the arrow bounces off and the bullet smashes through.

RE: What is the best way to get kinetic energy II
 

Arthur,
I agree with you on most everything you said but how about put a number on it? What initial level of momentum would you say is proper or should I say adequate for hunting whitetails with a bow?