Archery ballistics

this is a fairly good reconstruction of a medieval longbow war arrow it's got the feathery flats at the backend for stability and it's got the iron warhead at the front and in between the two it's got a long wooden shaft which is quite thick it has to be quite thick it's much thicker than a target arrow or a hunting arrow because the war bows used were very very powerful and the only way you could make an arrow stronger was to make it thicker so this is a thick shot to withstand the very substantial launch stresses so the archer would draw back his arrow and at this point it would be quite content and stationary and then he would release the string which would put a massive stress on one end of the arrow and this pushing would cause the arrow to bend and why would it Bend well it would Bend because of something called inertia things that have mass are reluctant to move and the more mass they have the more reluctant they are to move so you've got a length of wood that would rather stay still frankly and you suddenly push it that way and because there's a reluctance to move which I'll represent with as a as a resistance in my hand pressing that way as you put a massive stress on one end it burns so they had to be quite thick to withstand the launch pressures but actually there is an inaccuracy in this reconstruction because you'll see that it's equally thick all the way down its length this is a modern piece of Dowling I think it's cedar wood that's been produced by a machine I imagine and it's very easy for a machine to produce something today with even thickness all the way down its length but in fact long bow arrows weren't perfectly even in thickness all the way down their length and there's a reason for that that I'm going to demonstrate with this piece of balsa wood which fell out of the sky during a firework display now and where when I press on the ends of this piece of wood where will it break do you think will it break at some random point when it might because there may be some unpredicted weakness in the wood but it's even the wood is of equal equal strength all the way down its length it actually will break in a predictable way now if I take this adjusted spanner yes that's right I called it an adjustable spanner because I am British and I clamp this into the spanner oops wrong way and what you've got then is let's imagine I'm infinitely stronger so this is totally a mobile if I press down somewhere along the length of this it will break but where why I put at you it's going to break here and the reason is because this acts as a big lever when I push down so where the leverage yes that's right I said leverage I'm British is greatest it will cause the arrow all bit of wood to break okay it split a bit because they went down the grain but you can see it split up towards this end so if you get another one of these it was a big firework display and press in from either end where will it break will break where the stress is greatest because it's that's where the stress is being applied or or the other end well it's going to break in the middle isn't it this broke actually surprisingly easily again it's going to break in the middle because that this end is acting as a lever on the middle and this end is acting as a lever on the middle so the part of of the arrow where the the leverage of both ends is greatest in effect is actually the middle so yeah by and large they will break in the middle so if you want to make an arrow that's strong enough to withstand the launch stresses you need to make it thickest in the middle but actually the ends won't be subject to so much stress you could make those thinner and still the arrow would stay intact would survive launch and why would you want to do that well you might want to make the arrow lighter but there's another puck this equation you see as soon as you make the stick shorter you then have to put more stress on it to get it to break and all took a lot more and you can see still broke somewhere near the middle and if we then take stick that's shorter again and now you'll understand why I'm wearing gloves because this is going to hurt you have to put an awful lot of stress on it okay it didn't break the arts because it was where it split earlier but you can imagine it every time I break this it becomes harder to break by pushing it inwards from the ends and oh that really hurts now even through the gloves so what that means is that the crossbow bolt or quarrel by the way as far as I understand it the meaning of quarrel derives from the core as in quod quadrilateral quarter for a quarrel has a four-sided warhead on it or some square section thing and the bolt doesn't necessarily so that I think is why quarrels are called quarrels a quarrel in a crossbow it's about that long but the launch stress is on it can be huge because crossbows are often very powerful but because it's short it doesn't have to be very thick to withstand the launch stresses so a crossbow bolt can be the same thickness as a longbow arrow even though it may be subject to enormous ly greater poundage of bow and launch stress yeah now where is a longbow arrow thickest therefore I said that at the point of greatest stress so you might say in the middle but a longbow arrow isn't actually thickest in the middle and I think the main reason for this is the warhead now if I show you where the balance point on this is it's about there you see it's way off the center because this is the point in the arrow with the greatest inertia metal is much denser than wood so just as the centre of gravity is shifted forwards the inertia of the head is so much greater than the wood behind it that when you launch the arrow the point at which it bends greatest is also shifted forwards from the center so that is why when you look at a medieval arrow they tend to be barreled yes but the tenth bit they're thickest somewhere towards the front okay so that explains the shape of medieval arrows it also explains why crossbow bolts don't have to be quite so thick but there is more to this how far will an arrow go well it's based partly upon its weight think of a stone how far could you throw a stone well if I give if I gave you a a pebble like that or a little stone that's right I said stone or pebble not rock because I'm British you couldn't throw it anything like as far as a great big rock like this big rock like this you could probably just throw far enough so it didn't land on your toe and but a pebble that you could hold in your hand like that you could throw well further and why is that well it's because of the inertia the inertia of a really big thing is really difficult to overcome so if you are of constant strength then you won't be able to throw it very far but you being the same strength as you were when you try to throw the large thing trying to throw a smaller thing will be able to overcome its inertia and accelerated up to a much higher speed and so it'll go much further so the light of the thing the further it goes right no you know that's not true now if I take this stone here and this ping-pong ball you will see two objects are roughly the same size so which of these do you think I could throw further you know don't you I could throw this even though it's much heavier much further than this why can't I throw a ping-pong ball very far I can't throw it very far even though I can accelerate it up to very high speeds really easily because it's so light I can't throw it very far because as soon as it leaves my hand it will start slowing down very very quickly because of air resistance now if I climb on the moon where there's no atmosphere I know this is different but assuming I'm on earth and I'm trying to throw it through air this will not go very far because inertia is greater when something has more mass and that's the reluctance to be accelerated but momentum is also greater when something has more mass and that's it's reluctant to be decelerated so the forces of air resistance trying to slow this down will have a very easy time of it because it has very little momentum so in other words the wind can affect a ping-pong ball quite a lot whereas when I throw this it leaves my hand perhaps not going as fast but air resistance will slow this down very slowly because it's got a lot more mass a lot more momentum and if I try to select this with wind oh it did actually get it to move which I wasn't expecting but it doesn't get affected by wind anything like so much now just think how strong the wind is on something that's being launched from a high power war bow or crossbow the air resistance when it leaves that weapon is going to be very very high crossbow bolts you may remember are a lot lighter than longbow arrows which is good because that means they'll have very low inertia which means you'll be able to accelerate them really quickly up to very high speeds which is handy because you've only got that distance of span to accelerate it from stationary to maximum speed so having something very light is very useful and those of you who've taken part in science experiments at school where you've you've got a little car which you have to accelerate using a rubber band or a gas canister or something you will know that the lighter the vehicle the easier it is to get it up to very high speeds quickly so if you want to get something a long distance you want a missile with a lot of range you want it an ideal weight for the power of whatever your launch method is if it's the power of your throwing arm for a stone say for instance there's an ideal weight of stone for a given thrower if it's too heavy then you won't be able to accelerate it very fast and it won't go very far for that reason and if it's too light then air resistance will affect it too greatly and it won't go so far so there's a perfect weight of stone for you to throw and similarly there is a perfect weight of arrow for a given power of bow or crossbow I realized while editing this that perhaps I've been a little bit misleading so I should clarify not all longbow arrows by any means were barreled but many were if you want to shoot a frenchman who's not very far away you might want to clog him with a really big heavy stick so you just use a simple cylinder of wood for a narrow shaft and thwack him but if it's a very long way away you might select one of your specialist shooting Frenchmen who are a long way away arrows which would be perhaps barreled and it's called a flight arrow arrows designed to go a very long way and so their barrel to the strong enough to survive launch but they minimize weight by tapering to either end and so they're light enough to go a long way because light things go a long way because they're light but of course these hours have still be heavy enough not to be so light that the air resistance remember the ping-pong ball you were listening good so a light bolt with a thin bit of wood that's still because it sure what strong enough to withstand the launch pressure will survive the launch of a very very high poundage but short span and go up to a very very high speed really really quickly which is great but remember the ping-pong ball the quarrel is light it doesn't have the momentum of something much heavier so air resistance will have an easy time slowing it down which is why crossbows were really amazingly deadly up to about 60 yards because you try a crossbow and that that baa bleats leaps out of the weapon at very high velocity but after about 60 yards it slows down really quite significantly and if you try one into the air to drop onto the enemy they often reported as being unstable and doing this in flight as they come down and so at extreme range a man in armor being hit with a crossbow bolt to comp it's probably fine doesn't bother him that much but one of these dropping down out of the sky would still be stable because they were long enough and had better flights than a quarrel and when they hit you they would have the weight of the whole of that piece of wood pressing into you so at very long range you really don't want to be hit by a longbow little birds member

Channel: Lindybeige

Views: 596,608

Rating: 4.9518661 out of 5

Keywords: archery, ballistics, arrow, arrows, shaft, shafts, arrowshaft, shoot, bow, longbow, crossbow, twang, twangage, range, power, inertia, physics, momentum, air resistance, friction, air, weight, mass, thickness, wood, dowel, rod, length, leverage, warhead, head, arrowhead, fletching, string, launch, bend, paradox, archers, archer's

Id: J__NRSNv45g

Length: 12min 35sec (755 seconds)

Published: Sat Apr 30 2016

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