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Belated application of physics

So, I've heard that the energy extractable from wind goes up as the cube of windspeed. This is easy to follow: the kinetic energy of a mass of air goes up as v^2, and if the wind is v times faster, v times as much mass goes by, for a combined v^3.

Only today did it occur to me that this applies to wind blowing down on you, or your house: double the speed from 10 to 20 mph, octuple the energy involved. Suddenly, hurricane winds of 75 mph and tornado winds of 300 mph snap into perspective.

Perhaps more directly relevant to not being blown over is force, or delta-momentum. A mass of air moving v times faster has v times as much momentum, and again v times as much air mass can go by, so the force exerted on a stationary object goes as v^2. High everyday winds might be 30 mph; a tornado is not 10x as forceful, but 100x. Whee.

I suspect that in a fit of Galilean relativity, all this applies to propelling yourself through a stationary fluid, as well, but I'm not certain of that.

Tangentially, we live in a new era: avalanches on Mars visible almost live.

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Damien Sullivan
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