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Post by Caroline on Jul 3, 2009 21:17:52 GMT 1
Probably one of the most interesting threads on here.... can't wait for the experiment!
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Post by pembrokian on Jul 5, 2009 20:27:15 GMT 1
Well chaps & chapesses, here is the definitive answer from a real-life professor.
Just to set his answer in context here is the full e-mail exchange :
Dear Prof. Hatton, please excuse the informal approach but, having just read your paper on javelin throwing, you may be able to answer a question for me. In a recent discussion with a fellow thrower he claimed that high altitude would be beneficial for javelin throwing and I argued that there would be negligable difference.
I then went home and dusted off my textbooks from A Level Physics which I sat in 1983 prior to embarking on a degree in Chemistry - so second derivatives and triple integrals are way beyond me ! However, in our own simplistic way, we looked at a host of effects such as Archimedes displacement and reduction of gravitational acceleration before deciding that these effects were very small and it came down to two :
(i) viscous drag, a negative effect which reduces in thin air
(ii) aerodynamic lift, a positive effect which also reduces in thin air
My reasoning was that, as far as I could see, these forces both have a linear relationship to the density of the air, so the change in that density with altitude would have an equal, and cancelling, net effect.
I'm sure I have over-simplified the situation grossly. Without taking too much of your time, would you be able to offer a simpleton such as myself an understandable answer to our question ?
Many thanks.
Dr David Brown Liverpool Pembroke & Sefton Harriers AC Javelin coach and (very) amateur scientist.
The reply :
Dear Dave:
Thanks for the enquiry.
Its a complicated question which I don't really have a satisfactory answer to. In most of the simulations I have tried, introducing the air gives a small aerodynamic advantage, (maybe 3%). This suggests that altitude will slightly reduce the performance. However, you also find that delivering the javelin at a different combination of angle of release and attack angle can have a bigger effect.
To flesh this out, at exactly the same angle of release and attack, I would expect the javelin to fly slightly less far at altitude. However, its quite possible that for a different combination, it would go further at higher altitude (because the relationship between drag and lift effects can vary either side of 1.). The question then becomes much more complicated - if you are allowed to change everything, will it go further at high altitude or not.
So, don't know. :-) My guess is it would be hard to see much of an effect given all the other variables and I don't think there is an 'answer'.
Best wishes, Les.
Closing thanks :
Dear Les, thank you very much for taking the trouble to answer this. Actually I'm glad there isn't a definitive answer because, I think, that would take much of the fun and skill out of the event.
As, I suspect many of my colleagues and adversaries already knew deep down, javelin throwing remains an art that lies beyond mere computation.
Best wishes and sincerest thanks.
...so there you have it.
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Post by slinger on Jul 5, 2009 21:21:58 GMT 1
throws at altitude are marked with an A after the effort like sprinters who run wind assisted get a W Alex van der Merwe has a best of 74.62m at altitude but only 71.86m at sea level (below 1,000m i believe is the requirement) I know that david parker has an altitude throw of 78.33m compared to his PB of 78.24m His PB IS 78.33m Sam.
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Post by jeremy on Jul 5, 2009 23:25:38 GMT 1
Altitude is exceptionally important when it comes to speech; mostly the speech is of a higher standard: clearer too, when delivered from the mouth.
At an altitude approximately 2 - 3 feet lower than this, the alternative orifice for speaking is employed and generally the speech is less coherent: the air is also less clear around this part.
So for example if someone were to say "It is imperative that we spend £25,000,000 per year on a staff and infrastructures so as to support athletics from grass roots to elite", it may be possible to assume that the altitude level of this speech is at the lower of the two levels mentioned above.
If for example I stated that Chris Watts is good at ten pin bowling and can do so in size 16 shoes, then it is fair to assume that I am using the higher altitude for speech.
Final example is that if I'm having a chat with The Slinger about the spear, life, death, the spear, people and the spear, it is fair to assume that both parties will speak from a cariety of altitudes.
That's as best as I can explain things.
Jezza
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Post by sam on Jul 6, 2009 0:55:06 GMT 1
throws at altitude are marked with an A after the effort like sprinters who run wind assisted get a W Alex van der Merwe has a best of 74.62m at altitude but only 71.86m at sea level (below 1,000m i believe is the requirement) I know that david parker has an altitude throw of 78.33m compared to his PB of 78.24m His PB IS 78.33m Sam. Not according to power of 10. It shows his 78.33m throw as being at altitude down in south africa and his 78.24m as being his non altitude pb.
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Post by wez on Jul 6, 2009 8:41:29 GMT 1
Well done Pembrokian, although i don't feel very satisfied with a 'don't know' answer Maybe a statistical analysis would be needed of altitude verses non altitude throws for internationals. Unfortunately because of all the variables you would need a pretty big sample set. I'm thinking around 1000 throws over the same time period. Going back to fluid dynamics for a moment though, if air and water behave in the same way, then why is it that a javelin will not travel far under water given a similar release velocity if the density has no effect? By the way my Eton experiment went tits up! Too much human error- in my case i couldn't seem to throw without slipping over.
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Post by pembrokian on Jul 6, 2009 11:15:49 GMT 1
"if air and water behave in the same way, then why is it that a javelin will not travel far under water given a similar release velocity if the density has no effect?"
Struth you ask some bl**dy hard questions; I bet your teachers just loved you in school !
I don't have the expertise in areo or hydrodynamics to be sure of an answer but I can hazard a guess.
When we were talking about air I never said that density had no effect, in fact I did harp on at some length about at least two effects, drag and lift. Drag and lift both vary according to relative air density but the degree of that variation due to increase in altitude is small and , since one effect is positive and the other negative, they approximately cancel out.
With a much more dense fluid (like water, or if you wanted to be really extreme, mercury) the drag effect is huge and would reduce the velocity so quickly that there would, effectively, be no lift at all.
I'm guessing here, of course, but hey if a full-blown professor didn't know, I don't feel any shame in not knowing either !
On a more practical level I would like to know why statisticians have insisted in putting an "A" after such throws ? I'll bet a pound-to-a-penny they just assumed it would be advantageous without actually examining the physics behind it.
I seem to recall a young lady who is a member of this august forum was doing a degree in physics...lets put a call out for her input ?
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Post by wez on Jul 6, 2009 12:09:37 GMT 1
I do like to keep you interested....actually it was a loaded question. Water is very cohesive in nature with regular hydrogen bonding and polar orientation. Throwing a spear through it will need to break the hydrogen bonds which is gonna cost a fair bit of energy i'm guessing. The fluid dynamics might be the same but the fluid isn't. BTW i don't think the variation between lift and drag are so out of balance in water, diving birds have been shown to effectively fly underwater and i believe that lift may even become a far bigger factor in such a way that it is infact negative to optimum attack angle. This is way off subject now but it does bear thinking about the possible natural examples we can come up with to test the theory. Still what do you reckon about the throwing on the moon theory. There you can find a very thin fluid atmousphere and also lower gravity conditions which you do also get in a very minute way at high altitude on earth. It goes further there so surely it will at high altitude on earth also, but how much further 1-2m maybe? To be honest i don't think Prof Hatton even answered the gravitational part...or possibly several other relevant factors. Its far easier to write scientific papers when you take a simplified approach and ignore the bits you can't get you head round. We also have not addressed the biomechnics either have we, eg an athlete can run faster at high altitude eg more release velocity generated! It goes on.... My personal opinion is that its such a multi faceted question when you assume metabolics, biomechanics, physics and even chemistry there probably are no experts out there who have the answer. sorry Prof Hatton We can stab in the dark with all the various principles and theory but statistical evidence is where you will find your answer. This is very often the way it goes also in bioscience, we find out the results first and then try to figure out why. .....yes they loved me at school i found out fairly early on that just because someone has letters after their name doesn't always mean they have the answers...hell i've got some and i'm wrong about plenty of things....
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Post by sam on Jul 6, 2009 13:33:54 GMT 1
and we've all noticed that Prof Hatton is Felix's dad have we...
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Post by wez on Jul 6, 2009 13:42:09 GMT 1
No, wasn't aware of that but then i don't think i've ever thrown against Felix either so how would i have met him?
It might be a good talking point some time though if i ever do.
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Post by pembrokian on Jul 6, 2009 15:18:53 GMT 1
The gravity effect really is tiny, less than one part in 1,000 (or, for a 90m throw, less than 10cm). That's why they don't bother launching space shuttles off mountains, the benefit isn't worth the agro.
I never clicked the "Hatton" connection; is this known for a fact or just a guess ?
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Post by Caroline on Jul 6, 2009 18:41:52 GMT 1
I have to say that this sounds like a great subject as thesis material... imagine ....
'why are you warm weather training in Nepal/Dead Sea...?
so 12 months spent flying round the world chucking javs up mountains and down dales. Form an orderly queue please.... ;D
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Post by leshatto on Jul 11, 2009 6:44:02 GMT 1
Wez said: > To be honest i don't think Prof Hatton even answered the gravitational part...or possibly > several other relevant factors. Its far easier to write scientific papers when you take a > simplified approach and ignore the bits you can't get you head round. This is the first time I have ever posted anything on this forum but first of all thanks Wez for the help you gave us for Felix some months back. It was the start of a continuing but positive saga and much more on this later, although I am getting quite good at elbows. I hope yours is progressing well. I didn't mention the effects of gravity as its negligible as Dave suggested. Its perfectly possible to take account of most other things and the model here:- www.leshatton.org/javelin_2005.htmltakes account of all of the significant effects including the biomechanics of the thrower, (briefly if you throw it lower you hang on to it longer), rotation, pitching in flight, wind, lift and drag, as well as different nose cones (head and tail wind). This leads to an exotic set of non-coupled differential equations which are described in the paper Dave referenced. Its no big deal to solve them (aeronautical engineers do this all the time with wing design) and on a modern PC it takes about a tenth of a second. On the only two sets of data available, (way back in the 1990s), its within a metre at 85m which isn't too shabby when you include the wind. Please do feel free to download and play with it. Its been downloaded several thousand times around the world in the last few years so enjoy, or alternatively try to get out more. All I can say really is that the situation is sufficiently complex that it is impossible to reason about it in words. You just have to bash through the maths and compare it with measurements, (a classic characteristic of non-linear problems). There are a few things I could add, notably differences in javelin although the software can tell the difference between a tailwind and a headwind javelin. I would never try to compare manufacturers without a mountain of good data and this simply isn't available. Note that javelins behave like a thin aerofoil in flight and have both drag and lift depending on delivery angle, speed of delivery and the relative angle of attack with respect to the prevailing wind. The motion of a well-thrown javelin is a delicate balance between the centre of gravity which is static and the centre of pressure where the aerodynamic forces of drag and lift act. This moves in flight, typically by a few centimetres and is affected by the shape of the nose of the javelin. It also used to be affected by roughening the tail until that was made illegal. I was standing with Peter Yates at Crystal Palace a few months back and we found a roughened tail javelin lying round so we both had a go for old times sake, although his went a bit further than mine. I would like to think it was because he is ten years younger than me but that would not be telling the entire truth. :-) I hope this is useful. Best wishes, Les.
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Post by pj on Jul 11, 2009 10:14:02 GMT 1
Welcome to the JCUK forum Les.
Your credentials are impeccable and a very thought provoking first posting.
I shall look at your 'model' explanation as soon as possible.
(Congratulations to Doogiehowser on this topic and for reinvigorating the 'Science bit'.)
I guess that prior to this posting you have been one of the many guests that we read have been looking in but not contributing, Les.
With yours and Sarah Bradfield's recent contribution, things are really looking up for the Forum.
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Post by leshatto on Jul 11, 2009 15:53:38 GMT 1
pj:
Thanks. Life is a bit busy so I will be an infrequent poster at best. The model is about as good as I can make it with the available data. The only two decent datasets I could find were the World 1991 and the BAF 1993, (the Hatton in there is Tony Hatton not me by the way). These were measured well with trackside high speed cameras by Roger Bartlett and collaborators. Unfortunately there was no wind information. My calibration was based on reducing the error as much as possible whilst using a consistent wind-profile for the day. Its persuasive but not proof.
The other paper referenced by Dave included javelin vibration. This was first studied by Professor Mont Hubbard at the University of California in the late 80s. It has an interesting effect, increasing lift in some cases, but without measurement data to support its contribution, its difficult to justify adding this complication.
Jan Zelezny was notorious for wobbling his javelins with vibrations of amplitude +/- around 20cm at the ends on a couple of clips I have seen. I'm surprised they didn't break up in mid-air.
PS, there was a typo in my first post. When I said non-coupled differential equations, what I really meant was non-linear coupled differential equations. Missed a word out there, which is par for the course these days. :-)
Best wishes, Les.
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