The Truth about Kinetic Energy and Momentum for Deer Hunting

Рет қаралды 12,172

2 жыл бұрын

As bowhunters, we have one goal. A well executed shot & perfectly placed arrow providing a clean passthrough. I want you to read that last line once more and then understand Kinetic Energy has less to do with our goal than what we've been fed. IF YOU ONLY RETAIN ONE THOUGHT FROM THIS ARTICLE, LET IT BE THIS.....ARROWS KILL THROUGH BLOOD LOSS WHICH IS OBTAINED WITH A BROADHEAD AND PENETRATION...WE NEED TRAUMA!!!
As bowhunters we've bought into the concept of high KE setups being better, but the truth of the matter is KE isn't the driving force behind our goal as bowhunters. Put a firearm in your hands and that statement flips 180 degrees.
Let's face it, there's a ton of buzz around arrow builds these days. 20 years ago folks were buzzing around speed, now terms like FOC, KE, P, and total arrow weight dominate the arrow lingo. There's constant jabber about kinetic energy of your arrow but not nearly as much talk about momentum (P). At least until you talk with someone who understands physics or a bowhunter who prioritizes down range energy and penetration.
WHAT IS KE
We know that KE is the function of speed and mass of a moving object without direction. In the bowhunting world an arrow at rest has zero energy. Work, being directional force over a period of time, must be done on the arrow by your bow. Seems obvious. PE or Potential Energy stored in your bow and string is transferred to your arrow launching it forward and giving it Kinetic Energy while in flight.
To calculate Kinetic Energy we can use the following basic formula.
KE = .5Mass x Velocity².
For bowhunters, we can take the total weight in grains of our arrow as Mass. Velocity can be speed of the arrow in feet per second. The final equation to calculate your arrow's KE will be
KE = (Mass)x(Velocity x Velocity)/450,800
This expresses KE in Foot-Pounds of Energy or the amount of energy needed to move 1lb, 1ft of distance. Keep in mind, there is still no direction with KE and understanding this should force us to realize KE is not doing the killing with an archery setup. It simply tells us how hard the arrow will hit our target, but it becomes more into play when bowhunters choose to shoot mechanical broadheads.
WHAT IS MOMENTUM
You probably heard the saying "An object in motion stays in motion, until...."? If you have that understood, then you understand the concept of momentum. In bowhunting terms Momentum is simple, persistent force with direction or how much opposite force/resistance it will take to stop our arrow. Mass of your arrow multiplied by the arrow's velocity equals momentum. So we can note this as:
P = Mass x Velocity
For bowhunters, we can take the total weight in grains of our arrow as Mass. Velocity can be speed of the arrow in feet per second. The final equation to calculate your arrow's P will be in slugs FPS and can be noted as:
P = MV/225,400
Momentum is a vector quantity, so it has both magnitude and direction. Because Momentum has a direction, it can be used to predict the resulting direction and speed of motion of objects after they collide. For a bowhunters calculation, 1 slug is simply a unit of mass moving 1 foot per second when 1 pound of force in direction is enacted upon it.
All this sounds complicated but it boils down to this simple state. Our goals are passthrough shots, momentum being the resistance to a change in velocity is critical and THE most important aid in bowhunters achieving that goal.
Momentum vs KE Blog Article: bit.ly/3ydzj2t
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Пікірлер: 79

@danehale8637 2 жыл бұрын

I love reading the comments 🤣😂. As an engineer I've had to take numerous physics and math classes. It's nice having that foundation to understand these topics that apply to one of my passions which is archery. Id just say try not to over complicate things. Keep it simplified. Find a happy medium between arrow weight and speed for your particular bow set up. Also tune your arrows and make sure they are flying as straight as possible. Everyone is different. Some guys like light arrows some like heavy. Keep it positive and support your fellow hunter . We all don't have to agree on setups. What works for me might not work for you but what we all do share is the camaraderie of hunting!

@chadsyl23 2 жыл бұрын

💯 Dale! We appreciate you watching our content and taking the time to leave a comment! That means the world to us.

@danehale8637 2 жыл бұрын

Oh yeah and make sure you listen to deer hunter podcast 😂🤣

@timl8302 Жыл бұрын

This should be fun for you: kzfaq.info/get/bejne/b6uoqJuJ2cDblI0.html

@paulwakefield1015 2 жыл бұрын

Dr Ed Ashby is also an excellent resource for maximum penetration. Thanks Chad for addressing the subject.

@camthecameraman5096 2 жыл бұрын

Pretty happy with my current setup. Sitting at 456 grains

@YoureSoVane 2 жыл бұрын

Poncelet's equation, anyone? Seriously, there's an actual answer to this. You can roughly approximate it as mass*velocity^1.35 Mass has a bigger effect, but velocity is still important. On a modern compound at 70#, just go as heavy as you can tolerate for trajectory.

@PoeOutdoors 2 жыл бұрын

A huge factor ignored by mechanical broadhead users is how much energy is spent just to open one on impact. This becomes more relevant with lower weights/shorter draw lengths. Test the flight and durability of your arrows thoroughly and out a good fixed blade head on the end of it. One piece machined from solid steel (like VPA) is the best choice, but any fixed head > any mechanical.

@chadsylvester8336 2 жыл бұрын

Definitely can't argue that fact!

@ScratchGolfer0 8 ай бұрын

the amount of energy to open a mechanical broad head is not ever worth mentioning at 300 fps lol

@PBS-nm1uu Жыл бұрын

great presentation, looking forward to seeing more from you.

@steveyd101 2 жыл бұрын

For whitetail hunting distances (

@russelllangworthy8855 2 жыл бұрын

I agree with you. I shoot a lot of deer straight down and a heavier arrow with a fixed blade broadhead is much better for punching through the spine.

@chadsylvester8336 2 жыл бұрын

Totally agree. Distance is the equalizer when looking at velocity and momentum deprivation.

@steveyd101 2 жыл бұрын

@@chadsylvester8336 yes. but for whitetail, the distance where arrow weight affects speed enough to make a difference should not be an issue. If anyone misses a whitetail at 30 yards because their arrow weighed 100 grains more should not be blaming the arrow lol.

@The-Gun-Show Жыл бұрын

Yes and no. I had a 29.5 in draw 70lb bow and hit the shoulder of a deer this year with 594 grain arrow tuned to shoot groups out to 100. I was using a fixed blade that I sharpened. Not sure how I didn’t get a pass thru but it definitely mattered what bone I hit😂

@The-Gun-Show Жыл бұрын

That was at 25 yards only had one opening and tried to thread the needle

@thetinemen4842 2 жыл бұрын

Awesome info!

@cameroncunningham687 2 жыл бұрын

Damn ol dude is slapping that tigger 😂

@indy5797 2 жыл бұрын

270 to 290 fps is a sweet spot for a hunting arrow. Over 290, flight can start to degrade, and under 260 can cause trajectory concerns. I bulld for around 280 fps. For my stats (30", 70lb, 350 verified ibo) this translates to a 520 to 530 grain arrow. If I was in a situation where my shoulder could only handle 60lbs or my draw was 26" I would keep arrow weight up to meet momentum requirements and make a trajectory sacrifice rather than shoot a very light arrow. I started shooting a bow 35 years ago, so you can imagine that trajectory has never been a huge concern for me, and should probably not be for you unless you are shooting past 45 yards or at very small game.

@chadsyl23 2 жыл бұрын

That’s good advice! Aerodynamics start to have an effect at those speed, I believe that’s probably what you start to see your flight degrade. I’m pretty sure that starts around 270 fps but amplifies any issues the higher the velocity.

@indy5797 2 жыл бұрын

Yep, the more out of tune the bow and or arrow the earlier it starts! Always do a final broadhead tune to determine / mitigate this. I keep my old worn-out targets for this step.

@indy5797 2 жыл бұрын

Twill94, we are going to have to agree to disagree on flight degradation. 270 to 290 works just fine for me north south east or west, but hey, my limit is around 50 yards. Thanks for confirming my statement about 45 yards. Shoot whatever makes you happy.

@JZMartinez Жыл бұрын

What bow are you shooting with a verified 350ibo? With a shorter DL, I'll take a speed bow and mass.

@brokenarrow6491 Жыл бұрын

@BOWHUNTER I agree. I'm at 315 fps and my set-up is deadly on whitetails

@chrismacomber9727 2 жыл бұрын

Great video guys ...alot people say ohh I want my arrow sticking in the ground on the other side but seems to me anything after it passes through is a waste ...I try to him that happy medium we're I get two holes but the arrow don't need to go 30 yards after it goes through lol .

@chadsyl23 2 жыл бұрын

You are 100% correct!!! Thanks for watching.

@Antskillet 2 жыл бұрын

While this is true the arrow staying inside the animal will block some hemorrhaging therefor having more potential for low blood trails and internal blood loss. So you are correct it’s all the happy medium, but if your a hunter that likes to hunt elk hogs moose etc you might want to air on the side of heavy.

@chadsyl23 2 жыл бұрын

@@Antskillet the goal is always a pass through as mentioned in the video. When you calculate momentum you’ll realize you don’t need to be as heavy as “people” preach. For example a 450gr setup at 300 fps is .59 slug fps….. that will go through anything in North America.

@chrismacomber9727 2 жыл бұрын

@@Antskillet yes I agree brother I should have said that I live in NC hogs are not all that big and deer are smaller body's to...

@russelllangworthy8855 2 жыл бұрын

It's always better to have a complete pass-through. With the deer carrying the arrow, there's a far greater likelihood of the arrow being broken or damaged when the deer piles up.

@JoeyBaby47 2 жыл бұрын

I just started shooting a bow and have bolts with 100g tips and 125g tips. I can tell my 125g tips drop a lot fast than my 100g tips. At this moment, I feel more comfortable with a flatter trajectory arrow.

@chadsyl23 2 жыл бұрын

Ideally you carry maximum mass that provides your ideal trajectory. Glad to hear you are tinkering and learning for yourself first hand. Thanks for watching!

@philliparm Жыл бұрын

Momentum being such an important factor in penetration raises this consideration, once the arrow strikes the target animal a massive deceleration takes place and so a corresponding high loss of momentum. Mass on the other hand will remain constant. By manipulating the momentum equation by ‘weighting’ (sorry) the mass component rather than the the velocity one, momentum will remain comparatively high after impact greatly improving penetration and lethality.

@brokenarrow6491 Жыл бұрын

Good video.I don't understand why people make this so difficult. Shoot the proper spine, tune your bow and match the broadhead to your particular setup. If your shooting a lower poundage/energy bow bump up the arrow weight a little and use a two blade broadhead. If your shooting a fast bow at 70 lbs you can pretty much shoot what head you want. I'm shooting a 345 IBO bow at 315 fps with 375 grain arrows and a mechanical that cuts 1" going in and 1.75" coming out. I blow through whitetails and break bone with no problem. I shot a buck at almost 30 yards and I broke both front shoulders. I shot a sharp quartering away doe and it entered in front of her hip and came out at opposite front shoulder. I shot a deer last year and broke the exit side leg at the joint and had a complete pass through. A lot of people say this can't be done unless you shoot a heavy arrow, a high foc and and a fixed head and it's just not true. I shot a buck in 1973 with a 45 pound recurve but I was so small I was only shooting about 30 lbs with a bear razor broadhead and the arrow stuck out the opposite side of the deer. So the broadhead still went through shooting 30 lbs. I can't imagine how terrible the kinetic energy and momentum was with that setup but I killed the deer. I've been bow hunting for 50 years and I've tried just about everything and the set-up I have now is by far the best I've ever had for whitetails. Shoot what works for you and what you have confidence in. Be aware of heads that take a lot of energy to open. Stay away from those especially if your shooting a lower poundage bow. It's not easy trying to drive a 2" cut through the shoulders. That being said if ii was going for moose or elk etc I would shoot a different head and arrow weight. I would adjust my set-up to the game I was hunting.

@russelllangworthy8855 2 жыл бұрын

Kinetic Energy is a useful stat to judge different arrow setups. It may not be the most important factor, technically, but I still want the highest KE possible. You can have KE without momentum (figuratively) but you can't have momentum without KE. Chuck Adams wrote about Kinetic Energy in his book, "Bowhunter's Digest 3rd Edition" back in 1990.

@chadsylvester8336 2 жыл бұрын

100% We actually mentioned that....focus on the right momentum and you'll have the right KE. The big difference is that KE priorities speed and momentum leans towards mass due to the KE=M*V²

@bloodlines9610 2 жыл бұрын

I completely stopped stressing over all of this. Guys hunt with recurves with wooden arrows and 45lb draw and absolutely smack deer. So just hunt and be happy.

@h2olove 2 жыл бұрын

I think you are right not to stress over this. None of this should become stressful. There is a range of good answers. Historically, those recurves used heavier arrows. It was just the way they were made. It is important to know why something works as well as how well. Otherwise you can't apply it to other situations.

@torisglory4god 2 жыл бұрын

This gonna be a never ending argument/discussion. 🙄

@chadsyl23 2 жыл бұрын

😂

@TheTylerKline 2 жыл бұрын

What’s the equation to figure out .4 feet slug per second?

@chadsyl23 2 жыл бұрын

Mass (total arrow mass) x velocity(down range arrow speed) /225,400 For example a 450gr arrow at 300 fps is .59 slug fps

@garrettrowe7917 2 жыл бұрын

Good info, only thing I disagree with is when you said your bow loses efficiency when arrow mass goes up. From what I’ve gathered the heavier the arrow, the less potential energy is lost in sound/vibration (that’s why bow gets more quiet with heavy arrow) thus the arrow is absorbing more of the bow’s energy. I’m not saying to shoot 1000 grain arrow, you need to find your happy medium of speed vs mass to get the trajectory that you are comfortable with. DIY sportsman does an experiment on this where he increases arrow mass all the way out to 1200 grains, and the bow efficiency never dropped, it actually continually went up on a slope when graphed.

@chadsyl23 2 жыл бұрын

That has always been our thoughts two however after speaking with multiple lead engineers from two of the larges bow manufacturers, each stated on record that their flagship models are designed and most efficient at IBO specs. This was a big surprise to us as well. Check out the episode of the deer gear podcast where the lead engineer from Mathews was interviewed.

@garrettrowe7917 2 жыл бұрын

@@chadsyl23 well, I’d like to see them defy the laws of physics. Only way to know is to shoot different weights through a chronograph and measure the KE and momentum of each one and see which one has the most energy.

@ICU2B4UDO 11 ай бұрын

Ironically, with Flow Dynamics, the lighter the arrow the greater speed is lost over a heavier arrow at the same distance...Fun, huh!??! Lol 😂

@msarchery7053 2 жыл бұрын

Personal preference no matter how you feel about it. I'm shooting a Hoyt Ventum @84 lbs 29" dl. Last years setup of 545 grain arrow tipped with magnus black hornets, this stopped in the offside shoulder just above the joint on a 23 yrd hard quarter. Deer went down within 60 yrds or so. This season is a lil more jacked, 585 grain with Iron Will single bevels. Mind you yes @ 292 fps there's a trajectory but 2 holes and stuck in a tree counts to me. Shoot what you are confident with, me... heavy wins. Long shots are possible, but most NE Ohio whitetail shots are well within 40 yrds. My 3d arrows are 460 grain and they hammer foam lol. Good luck fellas, happy hunting

@chadsyl23 2 жыл бұрын

Happy hunting! Thanks for watching

@dlane3206 2 жыл бұрын

Good thing you skipped the physics lesson because you have it wrong. Take two arrows with equal KE and differing Momentum and then compare to two arrows with the same Momentum and different KE and you will see that penetration correlates with KE better than Momentum. Norb Mulaney proved this years ago yet. That does not mean that Momentum is meaningless. A good way to think of this is KE represents penetration potential of an object. Momentum determines how that potential Energy is used. The truth is they are both important. I find it interesting that you say KE does not matter ... unless you are using a mechanical. Which is it? Does it matter or doesn't it?

@ericnewman971 2 жыл бұрын

I never had the pleasure of meeting Norb, who passed away before I met Dave holt. but I have spent time with Dave Holt. I have also taken Dave's test data and put it into excel charts. Same as with Joel Maxfield. If people want to test to see if momentum is the driving factor, they only need to build two arrows of unequal weight. I like 700gr and 350gr. Then match the momentum at the target. doesn't matter how far the target is. 15 yards is a good distance. Again match momentum at impact. I don't care what media to use. Animal, sand, foam, or gel. this test will show if momentum is what gives us the penetration. people need to learn to look at Force =ma. I think the video is funny as he started out saying miss information and he post a crap ton of it.

@dudesweetpro 9 ай бұрын

I’m sorry but you don’t know what you’re talking about. The work that’s being done is the parting of flesh by the head of the arrow. The arrow is doing work separating the deer to the sides of the arrow. There is also friction. If you shoot the same bow with a heavy arrow and a light arrow. Given the bow is imparting the same amount of energy to each. The heavy arrow will have more momentum. Valuable for glancing blows, wind and grazing brush. But it will penetrate nearly the same as a faster arrow with the same energy. Momentum is just an attribute of that body in motion. A lighter arrow which will drop way less making for more forgiveness at changing distances and spooked game, will hit and do the same amount of work parting flesh at the head vs a heavier arrow with more momentum. Factoring in drag the lighter arrow will be affected more however the coefficient of drag is tiny and is pretty negligible. These things are not super sonic causing shock waves or cavitation etc.. this problem is simple and I’m thinking fixed blades. I’m a mechanical engineer. And this view of momentum is crazy in the bow hunting world.

@zacharywaterfield9463 2 жыл бұрын

If KE doesnt matter and its momentum, a heavier arrow out of a recurve should out penetrate a lighter arrow from a compound using the SAME broadhead, we dont see this happening though. The ability to penetrate is based off the amount of work that can be done, KE gives us the ability to work (penetrate), momentum keeps that projectile from changing direction. Penetration stops once energy is depleted. You cannot give an accurate slug value needed for penetration, Ashby even says Momentum derived from mass is better than momentum derived from velocity, that statement translates to a trad bow will out penetrate a compound bow with matched momentum. Ashby also stated he didn’t use a compound bow much as it was always getting a pass through so no measurable data could be taken… If you want to improve penetration in a given bow, you can increase the arrow mass, as mass goes up so does KE, this is efficiency. Lots of test done by Joel Maxfield that answer these penetration questions. Animals are the worst test media due to their inconsistent nature. If arrow A out penetrates arrow B in 10 out of 10 consistent mediums, a logical conclusion can drawn. Shoot what you want to shoot and find a balance between arrow mass and trajectory for what you want to do.

@zacharywaterfield9463 2 жыл бұрын

ways I recommend to increase penetration in your current bow without increasing draw weight, first a broadhead change then arrow mass increase. Increasing draw weight shows better results in penetration on consistent mediums than a mass increase, its more energy behind the projectile. Ashby showed what was needed to achieve like penetration with a trad bow as a compound bow gets, it took alot of mass and good broadhead design (as there is a huge difference in the amount of KE output). Look at some of the test Joel Maxfield has done and how they are backed by what physics tells us. If we take that trad arrow build and put it in a compound, obviously itll do even better but there are also draw backs to “downgrading” your modern equipment with tradtional arrow builds. As long as your are comfortable and confident in the setup, SEND IT and who cares what others think.

@jessedavis3196 2 жыл бұрын

Thata exactly what we see. Trad archers getting passthroughs with heavy arrows and compound boys shooting light arrows with expandables getting arrows stuck in ribs. Lighted nocks dancing as the deer hauls ass.

@aaronward3882 2 жыл бұрын

🙋‍♂️ you skipped over the first and most important step in the hunting arrow build.

@chadsyl23 2 жыл бұрын

We are all ears Aaron… even though the video was not intended around step by step arrow building.

@roderickmcleod4864 8 ай бұрын

I hate to be that guy, but, you have everything backwards, kinetic energy lets you know the distance needed when applying a given counterforce to stop an object momentum lets you know the time needed. I'm no bow hunter, I'm just taking phys1 at college, but it becomes clear when you look at the units for momentum and the units for KE. KE is measured in Joules (kg*m^2*s^-2 or kg(m^2/s^2)), and momentum is (kg*m*s^-1 or kg*(m/s)) if you divide KE by newtons (kg*(m/s^2) or kg*m*s-2) which is force, and in this case would be the deer's guts pushing on the arrow, you get distance, whereas with momentum u are left with time, so actually your shock which would be determined by jerk (m/s^3) will end up being determined by the change in momentum of the arrow before penetration divided by the spring constant (kg*s^2) of the deers skin, you could get this by seeing how much the deers skin deflects given a force. and this tracks, because your jerk would change with whatever tip is on your arrow, a more blunt tip would make it harder to initially penetrate the deer causing a higher change in momentum (or velocity) before penetration, giving high jerk, whereas a sharper and lower profile tip would have very little jerk. so if you were to actually calculate how deep the arrow will go, you would take your difference in velocity while the arrow is trying to penetrate the deer, multiply that by the mass of the arrow, to get ur change in momentum, then divide that by the spring constant to get ur jerk, then you would take the final velocity you used for that, find the amount of force that is required to push the arrow through the deer after penetration, and you can find your KE with (1/2)mV^2, then divide that by your force to push the arrow through the deer, and you will get a distance assuming you used all the right units depending on what measurement system you are using. it will be in meters if you use metric like I did. you could also just use the initial velocity and a maximum force for penetration and take a different route with the equations and arrive at the same answer but I've already spent way too long on this comment. this probably will go unnoticed, but the increase in understanding has helped me with my lab question, lmao.

@TheBladeSled 5 ай бұрын

Another engineer here. You guys are great but this physics lesson was a little awkward. you don’t actually understand what you are saying in this video.

@ericnewman971 2 жыл бұрын

Your physics is off. First, you need to learn what scalar means. I would suggest finding you a physic professor.

@chadsyl23 2 жыл бұрын

I’m not sure where this going but I well understand the difference between scalar and vectors. One has direction one doesn’t.

@ericnewman971 2 жыл бұрын

@@chadsyl23 no, scaler means no direction is needed to show KE. That means when we state that an arrow has 70ke we do not need to talk about direction, only magnitude. Momentum is a vector. which means we have to give it a magnitude and direction when showing momentum. This is one of the biggest miss understood things. people think that when an arrow impacts the ke is dispersed in all directions and then is gone. As long as the arrow is moving, it has energy. if the ke was dispersed on impact then the arrow would have stopped.