下面是那位不知名人士的email：

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On Sunday, January 2, 2022, 02:43:05 PM EST, Vess Velikov <[e-mail]> wrote:

 

Hi. I just read your article "Self-feedback Perpetual Motion and Violation of Thermodynamics Laws" about Rick Cavallaro's Blackbird and similar DDWFTTW carts. In it you seek to solve the paradox of their apparent violation of the laws of thermodynamics. To pick this apart, the article spins away into various scopes of definition, types of perpetual motion, global vs local accounting, succumbing to entropy, etc.

 

But there is no paradox to solve. The cart does not use perpetual motion, claimed or apparent. The energy source is the wind, defined as the differential motion between air and ground. If there is wind, there is energy to power the cart. If there is no wind, there is no energy. Simple as that. Same as any other wind-powered device (like a sailboat, or wind turbine). The need to spin off into philosophical depths to find a solution to an energy problem for Blackbird, is the same as for a sailboat; that is to say, none.

 

One twist is an intuition that throws off many people when thinking about this, and that is thinking about the differential motion of air vs. vehicle; and if this was the energy source, then it indeed disappears once the vehicle reaches wind speed, and then (to make matters even worse) reverses. But this is not the energy source; it is the differential motion of air vs. ground. And this stays the same regardless of vehicle speed. And DDWFTTW carts have a clever arrangement of parts, that sits at this interface and taps into this energy no matter the vehicle's speed, or relative/apparent wind.

 

In a more fine grained view, very simply put, the energy comes from the air processed by the propeller. (This is in the ground frame of reference, but you can analyze from any frame of reference for the same result). The air (blown backward) slows down, therefore its kinetic energy is reduced, and this kinetic energy goes into the cart, used for a combination of acceleration and thermal loss (mechanical and aerodynamic). Mostly acceleration in the beginning, tapering to no acceleration and all thermal loss at the steady-state DDWFTTW speed.

 

(Your Appendix I analysis contains a fundamental error about the torque on the propeller at faster than wind speed, but I avoided talking about it because it doesn't really bear on the points above. But I will, if you'd like).

 

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真不知今天的科学界的这种根本读不懂文章还自淫自嗨的毛病是怎么遗传来的。。。