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2 years ago
sooo knaughty with that remark. |
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2 years ago
Did you ever consider that maybe the problem is the wind meter. There is a lot of junk science in this discussion. The what really is happening is that the anemometer that they used to measure wind speed is not correcting for the difference in the air density (which does change as a function of temperature). It is not that 6knt has more power when it's cold compared to when it is hot but rather the accuracy of the instrument is off. Might want to take a physics class. |
I am not sure I agree with you, but I will think a bit more about it...
an anemometer will spin due to the drag force on the cups. The cups will reach equilibrium when they are spinning at such a rate that the apparent wind speed over the cups approaches zero. I don't think this value will change much with air density. Drop a feather in an air tunnel with wind going 5 knots and the feather will go 5 knots....drop it in a tow tank of water moving at 5 knots, and the feather will go 5 knots. For something small and light like an anemometer, the density shouldn't be a major factor.
What Alex is saying here is that the amount of energy, or power in a fluid is a function of its density and speed. So think of power for a sec, the units are Watts (Joules/sec or kg*m^2/s^3). Really what we are thinking about is the kinetic energy of the particles of the fluid. In fluid dynamics you can approximate the
fluid power as = 1/2 * density of fluid * velocity of fluid squared * volume of the fluid packet.
This will give you the "power of the fluid".
if you turn the crank on the math, this means that wind that is 25 degrees (celsius) colder will have approximately 10% more power (assuming you are considering the same size volume of fluid). Alex noted that riders went between 6.5 and 8.0 square meter sails, which is about a 20% change in sail area.
on another note, don't be too quick to judge, Alex is a super smart guy and has tons of experience. His discussion is not junk science.
and for reference...I have a M.S in Ocean Engineering and getting a Ph.D in Applied Marine Physics.