Gonna be a scorcher in Austin today

[gh]

My guess is any benefit is only measurable at velocities much higher than any sprinter can run.

I meant to posit that as well in my response. The 'aid' HAS to be less than .01 sec (IVHMO).

Empirical evidence suggests otherwise.

[La_Spigola_Loca]

Nitrogen gas is N2, with a Mw of 28.

[gh]

I've asked JRM to weigh in on this. Like having Suso comment on the Davis foul, I realize that getting a real scientist involved takes all the fun out of it, but hey....

[La_Spigola_Loca]

My most simplified calculation for 10.00 at 0% humidity gives 9.95 at 100% hunidity.

[bekeselassie]

I realize that getting a real scientist involved takes all the fun out of it, but hey....

Maybe we could have one of the scientists around here just PM his explanation to Squackee, and Squack could paraphrase it for us. 8)

[DrJay]

No doubt temperature affects longer distances, but the 1500? I don't know for sure, but here's something to consider. Even if the race distance doesn't seem to come into play so much in the heat, how about the warmups plus the race? For an 800 or mile my typical warmup was a mile-and-a-half before my accelerations and such. It took that much before I really felt everything was flowing just right.

In late spring, I'd step to the starting line already dripping sweat sometimes. So could it be argued that if we include the warmups then not only the 1500 is affected by the heat, but maybe the 800 as well?

Good point. I think it's up in the air as to whether the 1500 is slowed by hot temps, but if it's not, you can bet the athletes feel it worse in the 15 minutes or so after a fast (near PR) race. I bet if you measured core temps 5 or 10 minutes after the finish of a 1500 on an 85F day, you'd find some values in the 102-103 range, with said warmup setting things up for that.

[mike renfro]

The perfect weather for a track meet is 55 degrees, overcast and no wind. 8)

Not if you are sitting in the stands, shorts, sandals, tshirt optional. Give me the suntan days!

[donley2]

Here is JRM weighing in on the previous thread

http://www.trackandfieldnews.com/discussion/viewtopic.php?t=15273

[tlb747]

The perfect weather for a track meet is 55 degrees, overcast and no wind. 8)

I think both sprinter/jumper types and spectators prefer something a bit warmer.

Yeah, and I would be the exteme example because I love the heat. Perfect track'n'field conditions FOR ME is a least 90 degrees, with hardly any wind and humidity. I remember the 1998 Texas Relays (last held at the football stadium) was quite humid for me because I was running in Arizona at the time. As soon as I walked out of the Austin Airport, is was like the humdity just slapped me in the face. It was so bad that I can see it, slowly falling to the ground, almost like fog. The city is known to be a "Clean Air" city, but I know it as a "Slap in my face humid city."

[tafnut]

My guess is any benefit is only measurable at velocities much higher than any sprinter can run.

I meant to posit that as well in my response. The 'aid' HAS to be less than .01 sec (IVHMO).

Empirical evidence suggests otherwise.

I just used JRM's algorithm and using 10.00 on a 25C day with 1000 mb, zero wind, zero altitude I get zero difference between 100% humidity and 0% humdity. Am I doing something wrong?

[La_Spigola_Loca]

My most simplified calculation for 10.00 at 0% humidity gives 9.95 at 100% hunidity.

Eeep! I meant 9.995.
Let's do this again. The average force of your "average elite" sprinter, say a 70 kg guy, is around 4000 N, applied about 25% of the time of the race. Let's simplify this and talk averages:
100m, 10.00 at 0% humidity.
4000 N *.25 = 1000 N
Let's assume 10 m/s is quick enough for a drag impact, where the force ius proportional to the square of the body's velocity, or F(drag) = qV^2, where V is the body's veocity, and q is the drag coefficient. q for your average guy (say 1.75 to 1.80, 70 to 75 kg) is about 0.45 kg/m. Now 0.45 kg/m * (10 m/s)^2 = F(drag) =~45 N, applicable throughout the race. So we can assume the guy applies on average 1045 N, out if which 45 are F(drag).
Now F(drag) is linearly dependent on air density. On going from 0% humidity to 100% we'd be changing air density by about 2% (at 20°C and atmospheric pressure, the difference is between 1.204 kg/m^3 and 1.176 kg/m^3), or decrease F(drag) by around 45 N *.02 =~0.9 N, which our sprinter can now put into his speed generating force, increasing it from 1000 N to 1000.9 N.
10.00/(1000.9/1000)^0.5 = 9.9955. So, not really a measurable difference there.

[26mi235]

[quote=La_Spigola_Loca]

My most simplified calculation for 10.00 at 0% humidity gives 9.95 at 100% hunidity.

Eeep! I meant 9.995.
Let's do this again. The average force of your "average elite" sprinter, say a 70 kg guy, is around 4000 N, applied about 25% of the time of the race. Let's simplify this and talk averages:
100m, 10.00 at 0% humidity.
4000 N *.25 = 1000 N
Let's assume 10 m/s is quick enough for a drag impact, where the force ius proportional to the square of the body's velocity, or F(drag) = qV^2, where V is the body's veocity, and q is the drag coefficient. q for your average guy (say 1.75 to 1.80, 70 to 75 kg) is about 0.45 kg/m. Now 0.45 kg/m * (10 m/s)^2 = F(drag) =~45 N, applicable throughout the race. So we can assume the guy applies on average 1045 N, out if which 45 are F(drag).
Now F(drag) is linearly dependent on air density. On going from 0% humidity to 100% we'd be changing air density by about 2% (at 20°C and atmospheric pressure, the difference is between 1.204 kg/m^3 and 1.176 kg/m^3), or decrease F(drag) by around 45 N *.02 =~0.9 N, which our sprinter can now put into his speed generating force, increasing it from 1000 N to 1000.9 N.
10.00/(1000.9/1000)^0.5 = 9.9955. So, not really a measurable difference there.[/quote:14fsjl3l]

Without going through the math in the limited time that I have it is my impression that at 100m speeds of 10m/sec, the wind resistence is greater than 4.5% of the effort. Now the figure that I remember from bicycling is that at 20mph most of the effort is overcoming wind resistence. At 10m/sec there is more running friction than other bicycle frictional losses. However, it would take a lot for the wind resistence to drop to 4.5%

[La_Spigola_Loca]

If you have any figures for me, that is, total force required to overcome air resistance, at a given speed and for a rider of a given weight, along with the ratio of the rider 's "surface area" (facing the wind) to the total surface area of the rider + bicycle, they're more than welcome. I had to use an "accepted" drag coefficient for "humans" of 0.45 kg/m (at a stretched position). Again, any value better than that is more than welcome.

[26mi235]

If you have any figures for me, that is, total force required to overcome air resistance, at a given speed and for a rider of a given weight, along with the ratio of the rider 's "surface area" (facing the wind) to the total surface area of the rider + bicycle, they're more than welcome. I had to use an "accepted" drag coefficient for "humans" of 0.45 kg/m (at a stretched position). Again, any value better than that is more than welcome.

Because wind resistence is so important in bicycle riding/racing there is a much more developed literature (and culture) on the topic. A long time ago there was a book (Bicycle Science?) put out by the MIT press that was fairly definative at the time, but I am sure there are better things available. Another comment I remember that is running specific is that the reduction in wind resistence when drafting behind a runner at sub-4 mile pace was 7%. The wind resistence should be just more than double at sprint speeds and I seem to remember that "drafting" reduces wind resistence by 30%, but certainly that depends on geometry and speed.

I suppose that JMR knows more on this topic.

[La_Spigola_Loca]

Another comment I remember that is running specific is that the reduction in wind resistence when drafting behind a runner at sub-4 mile pace was 7%. The wind resistence should be just more than double at sprint speeds and I seem to remember that "drafting" reduces wind resistence by 30%, but certainly that depends on geometry and speed.

I suppose that JMR knows more on this topic.

A 7% or 30% drop in air resistance still doesn't tell me how much of the power input goes to overcoming air resistance. But ponder this- even if you find 4.5% too little (I personally don't, but it's very difficult to estimate such a thing from pure experience- ever tried to evaluate the viscosity of water you were swimming in? we are not really accurate measuring equipments :wink, I think 10% would be a gross overestimation, and even 10% would give a difference betweeen running 10.00 and 9.99 uncder conditions of 0% and 100% humidity, respectively.