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

That thread is really screwed up. I suggest for those of us who want to continue that we do it here...

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

The quickest way to get KE is to increase your speed. The quickest way to increase your speed is to make your draw length longer. If the draw length is too long you won't shoot accurately.

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

How do you increase your draw length?

[There now things are working!]

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

If you shoot a loop take it off. That will gain you a quarter inch...

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

With a 30" draw 7" brace and 60 pounds initially shooting a 350 grain arrow 265 ft/sec a 1/4" increase in draw buys me only 0.6 ft/lbs KE and 0.002 slug ft/sec momentum.

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

My point exactly, increasing your draw length is usually not an option. Like was stated in the previous thread, it's obvious that a heavier arrow will increase down range KE and momentum.

I just try to find a happy medium of trajectory, arrow weight and KE/momentum and put it in the boiler room

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

I agree completely. The discussion about KE and momentum is interesting and I enjoy talking about it but most of us are delivering plenty of energy/momentum and having more of it won't make up for poor shot placement.

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

Sylvan, on the other thread you asked why I use pound-seconds instead of slug ft/secs. I use pound-seconds because that is the way the ballistics program I use lists it. If you want to convert my figures to slugs, be my guest. They are the same values, just a different (maybe old fashioned?) way of listing momentum values.

For those of you who don't have a clue what we're talking about: Slug - The unit of mass that is accelerated at the rate of one foot per second per second when acted on by a force of one pound weight.

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

Interesting, I've never seen momentum referred to in pound/seconds. I wonder why they do that seeing that momentum = mass x velocity and the pound isn't a unit of mass and seconds aren't units of velocity. Slug ft/sec or kilogram meters/sec if you like the metric system are typically what you see in physics/mechanics. Technically what they use is incorrect. I didn't check your values but they appeared to be values that made sense as slug ft/sec. Anyway it isn't a big deal I just have never seen it.

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

Yeah, eventually somebody's gonna come along and list things in Newtons and really screw us all up. [8D]

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

Arthur P,
It's funny but when I was in freshman physics we did everything using metric units (probably because its easier). The prof never used eglish units in any examples and I don't believe there were any in the text book either. Anyway, on an exam he gave us a realtivly simple problem to solve but suddenly it was english units. Nobody got the right answer!

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

I am still waiting for someone to answer this.......

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

i can answer this for u, if u give up a little speed you will have a quieter bow. this will give you a chance at hitting that whitetail! sence a whitetails reaction time is 1100 f.p.s. [:-] i don't care how tough you are, you will never get 1100 fps out of a bow!
i hope that didn;t burn to bad, lol:D

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

As long as I'm over what I consider a minimum adequate amount of energy/momentum for the distance I'm willing to shoot I wouldn't give up any speed for energy.

Actually I think this was answered several times in the other thread. Several people said that delivering energy over the minimum needed only winds up wasted in the ground after it passes through the deer.

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

That looks like a reaction velocity.

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

I don't know what your problem is, the only thing that burns around here is reading your non-sense posts .

So Einstein how many grains and weight should I shoot as 70# and 400 grains don't fly for you on a hunting setup? As you seem to have the holy grail of archery knowledge.

I shoot around a minimum of 200 arrows per week this time of year between my two indoor 5 spot leagues, indoor 3-D league and outdoor 3-D on the weekends. How about you?

How about we toe the 3-D line??? I don't think you want that "TOUGH GUY";)

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

buckeyebuckhntr,
I wouldn't waste my time with posts that make no sense. I think somebody has been smoking something other than the targets!

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

Good enough:)

Syl IYO what do you consider adequate energy?

For inside 40 yards I like to have around or better than 65 ft/lb of KE at point of release.

It got a little hard to follow with all the posts not showing up[8D]

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

wow! i have never seen a 3-d target move! that could be fun!:D my knowledge goes way beyond the bow arrow setup

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

Can I get any one that can figger it out how much KE I am getting?
Allso all you supper smart people HOW much MOMENTUM am I getting?

I get 297 fps bow is set to 90# 29 in draw, shooting 2514 xx78 arrow is 550 grs

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

108 Ft/lb of KE

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

You got that right.

I'm no expert but from what I've read, 35 ft/lbs is adequate for whitetail deer. If you back up 40 yards and 35 ft/lbs I'd guess maybe that translates to around 40 ft/lbs at launch so I would think you've got plenty of punch. For the past 10 years I've been launching pretty close to 50 ft/lbs. The farthest I've taken a whitetail is only 35 yards but the arrow passed through and was buried maybe 6 inches in the ground. In the last 10 or 15 years I don't think I've ever not had the broadhead poke a hole through the other side of the deer. Maybe not fly into the ground but holes both sides none the less.

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

Syl did you pick up the Old Glory? Sure is a sweet shooter.


As I posted earlier when the tough guy nazi showed up my Allegiance pushes 80ft/lb of KE at 70.5# 299.6fps and 400 grains.

That is unreal!

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

No, I'm still debating with myself. It's a fair chunk of change and I've bought quite a bit of other equipment lately so I'm thinking I'll wait a while. Funny though I took a friend to look at one. He shot it (an Old Glory) and ordered one a couple days later.

I'd say you're set for any big game animal in North america, probably Africa too.

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

Are you guys glad i started this????

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

How about this why would someone give up energy/momentum (Which kills the animal) for a trivial amount of speed? I just don't see it.

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

Well E when is enough.... enough? 400 grains at 80 ft/lb isn't enough? Where do you stop?

Ok lets add 210 grains and subtract 70fps....


SO 610 grains at 230 fps only yields 72 ft/lb of KE

Perhaps I should shoot that setup instead from what you are saying?

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

Momentum in slug ft/sec = Arrow weight in grains divided by 225120 times velocity
Kinetic Energy = Arrow weight divided by 450240 times velocity times velocity.

In your case momentum = (550/225120) times 297 = .73
Kinetic Energy = (550/450240) times 297 times 297 = 107.8

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

Speed gives you a flatter trajectory which actually improves accuracy which of course is a good thing. As long as you have "excess" energy to do the job that energy will be wasted unless you channel it to velocity where it can be used to flatten the trajectory. Let me exagerate to make the point. Lets say it takes 10 units of energy to pass an arrow through a deer and lets say you have 100 units available. Theoreticaly you could shoot an arrow through 10 deer if they were lined up just right. But wouldn't it make more sense to use say just 20 units for driving the arrow through and the other 80 channel into velocity? You're still sure you can kill the animal but you also are putting the exess energy to good use rather than wasting it.

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

Buckeye why don't you ever look at momentum. It is what determines penetration. Put in an arrow that goes 1000FPS at 40 grains. What is the KE? More than your arrow, would this arrow penetrate better than yours? NO so look at Momentum, hey what do you know, it has a lot less momentum than your arrow. It only makes sense, if you think about it. :eek:

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?