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Post by doogiehowsermd on Jun 30, 2009 11:16:58 GMT 1
Watching the lions game on Saturday and that winning kick from 54m made me think about the effect of throwing at altitude. If a rugby ball goes further would a spear do the same?
Is there anyone with experience of this or knows of good throws at altitude?
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Post by sam on Jun 30, 2009 11:28:30 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
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Post by wez on Jun 30, 2009 11:33:05 GMT 1
The air is thinner at altitude so that in theory means less wind resistance but given that javs fly further with a good following wind it would also mean less push from behind and the tip dropping down earlier.
Maybe throwing in non-optimal winds would in theory go further at altitude. I don't know any specific examples though, but the same thought has crossed my mind before....
How about world class throws....anyone?
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Post by doogiehowsermd on Jun 30, 2009 14:02:03 GMT 1
can you also achieve a qualifying standard at altitude?
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Post by sam on Jun 30, 2009 14:28:17 GMT 1
i don't think so but will check and get back to you
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Post by pembrokian on Jul 1, 2009 11:08:12 GMT 1
I would imagine that there are (at least) two conflicting effects that suffer and benefit from the thinner air at higher altitude.
On the one hand for any object moving through a fluid (air is a fluid, just like water) the less dense the fluid is, the less the resistance to motion. The viscous drag on a body moving through a fluid is directly proportional to the fluid density and the velocity of the motion.
But there is another factor which doesn't apply to rugby balls but does apply to javelins and that is one of lift. Because of the aerodynamic design of a javelin (especially the posh, expensive ones) they generate their own lift as they move through the air. This lift is also proportional the the density of the fluid but is proportional to the velocity squared. Thus the lift force tails off very much more rapidly than the viscous drag as the javelin slows.
I can't see at first inspection why altitude would make a significant difference since the air viscosity/density has a similar effect on both lift and drag.
However, never underestimate the effect of psychology on that superstitious creature known as "the thrower". All you have to do is tell them it will go further at altitude and, within minutes, there'll be a queue out of the door at the BA check in desk !
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Post by wez on Jul 1, 2009 12:29:05 GMT 1
Actually Pembrokian to be pedantic....air is a gas and not a liquid! Here comes the chemistry lesson......Gas molecules are very light and fast moving and very weakly bound to eachother allowing things to pass through them easily. If you were to pressurise air you would get a liquid. In 'fluid' dynamics though it seems that they act similarly. If the formulas you mention are correct (where did you get them?) then it means the thinner the air the further the implement will fly given that high velocity causes far more drag than its does lift- velocity squared is a much bigger number. eg a 90m throw= 30m/s release velocity which is proportionate to drag and only its square root of 5.47m/s for lift....at jav throwing velocities you get alot less lift. That means that the density of the air does make a big difference as drag is a considerably bigger negative factor than lift as a positive factor. So to sum up thin air makes you throw a javelin further. The question is how much thinner is it up there? and do you get the same powerful tail-wind conditions you might find for example in a track situated in a valley for example?! I might build a jav runup on a high altitude plateau between two mountains in order to channel the wind through. Would you be able to get legal throws there? i doubt it.... If anyone could be bothered to read this far well done, now go and find something more useful to do with yourself. Just joking its a relevant point.
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Post by wez on Jul 1, 2009 13:13:25 GMT 1
Just thinking about it further, i don't believe that a javelins aerodynamic properties give it lift! What they can do is to buff the air out of the way with a spinning blunt end which reduces air drag on the shaft as it passes by. On the other hand having a strong tail wind pushing behind will favour friction on the under side of the shaft near the point giving a slight upward thurst to the tip allowing it to fly flatter on the way down and hence go a bit further. One other thing in favour of altitude throwing is that gravity is slightly weaker at high altitude (although it proportional to altitude squared unfortunately) and hence your jav won't come down quite so fast. To get a noticable effect though you need to be at very high altitude. On top of mount everset at 9000m gravity is about 9.5m/s/s vs 9.8m/s/s on sea level. If you could find a track even at 5000m you could well get an advantage from weaker gravity maybe 0.2m/s less for every second it is in the air. So it will fly higher and fall slower and go further, then the thin air ontop of that should help also. Take a look though 0.2m/s and a jav is in the air for what 3 seconds? thats 60cm! The longer you could keep it up there the further it would fly so this is where thin air may have a combined effect. I think i should go and do something with my life now...
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Post by pembrokian on Jul 1, 2009 15:30:31 GMT 1
Wez, the gloves are off ! I never said gas was a liquid; I chose my words very carefully when I described it (accurately) as a fluid. A thrown aerodynamic javelin does generate lift since, in cross section, it resembles an aeroplane wing insofaras the lower surface provides a shorter, faster route for the fluid to pass across than the upper surface. You seem to assumed that a javelin thrown at sea level must be slower in some way ? For a 30m/s release velocity at sea level or high altitude the effect of the air viscosity will be the same for drag or lift because the gas density term is linear for both effects; it is the velocity term that is squared. So, as an ex-physics teacher, how confident am I about all this ? Not very ! Because I'm sure this is all very simplified (though I am happy with the basic equations, Stokes & Bernoulli's). Now I will have to go and find out about it; because I'm very sad like that. Damn you Doogie Howser !!!
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Post by doogiehowsermd on Jul 1, 2009 17:14:30 GMT 1
does air temperature have any effect as well? Assume hot air is less dense?
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Post by pj on Jul 1, 2009 20:44:15 GMT 1
I've had a nice game of golf this afternoon, just watched Murray and A-Rod win at Wimbledon and after reading this just lost the will to live !! Where do you guys get this stuff from? I did Sciences at A Level a long long time ago. Perhaps I have forgotten everything?
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Post by wez on Jul 2, 2009 8:11:44 GMT 1
Lol this could go on and on, Pembrokian you got me there, i assumed that you meant liquid when you said fluid....thats my biochem throwing a spanner in the works. Well good that we are reading from the same page anyway Back to the lift bit, you said "This lift is also proportional the the density of the fluid but is proportional to the velocity squared" and "The viscous drag on a body moving through a fluid is directly proportional to the fluid density and the velocity of the motion" Meaning that they are not equal when assuming velocity as constant??? To me that tells that lift is a smaller factor than drag so then the thinner the air the longer your throw. ... just had a look at the equation and as far as i can see the above is a bit misleading, and like you say it suggests equal forces in lift and drag. Still i'm not convinced by the lift thing for a jav though. An aeroplane wing works on the principle that it is flat underneath and curved ontop so the air moves faster over the top creating a a gradient in air pressure. eg low pressure above the wing causes the higher pressure underneath to push the wing upwards. I don't see how a jav can do this given that it is symetrical across its axial point. I mean underneath and ontop it is the same shape. I can only see there being an effect when it effectively tilts in the air so is no longer flying through the point but the dynamics of the shaft have more effect. As i see it the tip of a jav if blunt is curved so it causes the air to move faster over it than it does on the shaft, so the shaft is in low pressure and can slip through more freely a bit like slip streaming in formula one. Maybe a diagram showing lift of a javelin would help here. I'm still not convinced. Doogie, if thin air helps a jav fly then indeed warm air is also thinner as the gas molecules are moving faster due to the extra kinetic energy and they bump eachother apart. Are we any closer to finding the answer to "If a rugby ball goes further would a spear do the same?" i'm not sure, i bet its more complicated than we have discussed which makes me think of weather. Low pressure weather must be better for throwing when its cloudy and close to a storm and high pressure when its clear and sunny would make throwing more difficult. Back to altitude for a moment though and don't forget the weaker gravity factor- we all know what happens when someone hits a golf ball on the moon. There is very low gravity and very thin 'fluids' which has to be a working example and proof that such conditions are better for throwing. Its the closest extreme example your going to find to mimic lets say VERY high altitude conditions. One last thing, even assuking that high altitude make the jav go further. The athlete themself gets less oxygen in the blood due to the thin air and has less energy to throw.... If anyone is still reading by this point then i seriously doubt you have ever picked up a javelin in your life let alone left your computer for more than 10 minutes at a time to find sugar based snack food. So is this really relevant to you just found this..... www.leshatton.org/Documents/jav2007a_paper.pdf
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Post by pembrokian on Jul 3, 2009 0:49:48 GMT 1
I've emailed Prof Hatton for his opinion. If you thought that paper was bad just try wrapping your grey matter round this one : versita.metapress.com/content/q2118327nk154h56/fulltext.pdfThis one : www.faqs.org/sports-science/Ha-Ja/High-Altitude-Effects-on-Sport-Performance.html...suggested that "any objects thrown, such as a discus or javelin, would tend to travel further as well", you are correct but it's not the most scientifically written document I've ever come across. This one : masterstrack.com/blog/003420.html...seems to back my own beliefs "Altitude is a detriment to the javelin, discus ... The loss of aerodynamic lift is much greater than the gravitational gain for both javelin and discus.", but, to be honest, it doesn't cite where it gets these results and is equally amateur in it's approach. So we'll just have to wit for a response from prof Hatton. Some things I can confirm : (i) gravitational acceleration at 2300m (Mexico City) is 99.928% of that at sea level, a tiny effect. (ii) a javelin in air at sea level "loses" 0.869g due to Archimedes displacement in air, at 2300m this is only 0.695g but still a minute effect. (iii) physiologically the thin air would have almost no effect on an anaerobic event such as a throw; in the Mexico games new World records were set up to the 400m. Only endurance events really suffered from the thin air. Now to send of my application form for the Little Middleton & District Train Spotters Club.
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Post by wez on Jul 3, 2009 9:25:47 GMT 1
You know what, theres so much theory and minor contradiction that there is probably only one way to trully solve the problem and that would be experimental data. I'm visualising a portable wind tunnel, and jav launcher.....people just aren't reliable enough! To be honest though i think you would need to get higher than Mexico city to get a significant effect, more like 5000m i think. I wonder if there are any really high tracks? I tell you what i have learned from this episode, i will be trying to keep my jav at the optimum attack angle and putting on as much spin as possible. Tomorrow at Eton will be my test field
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Post by pj on Jul 3, 2009 9:34:33 GMT 1
Hi Wes,
Here's hoping the 'fluid' is good.
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