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Big News! UCLA Physics Prof, @alexkusenko bet me $10,000 that I'm wrong about going downwind faster than the wind. //www.youtube.com/watch?v=jyQwgBAaBagOur wager was witnessed by @neiltyson@BillNye@seanmcarrollIf I win, to what charitable cause should I donate the funds?
Here is a set of 10 slides that (1) explain what is seen in the video (2) point out the errors theoretical arguments, and (3) provide a complete solution to the problem.
Replying to @thephysicsgirl @alexkusenko and 3 othersCome on! If someone emails me saying I’m wrong, first I try to convince them that I’m right. Then if we continue to disagree I suggest we make it interesting. The key is to get to the truth. The best, scientifically accurate explanation should win.
Some literature on the subject Wikipedia page: https://en.wikipedia.org/wiki/Blackbird_(land_yacht)[1] Md. Sadak Ali Khan, et al, “Analysis of Down-Wind Propeller Vehicle”, International Journal of Scientific and Research Publications, 3, 4. (2013) http://www.ijsrp.org/research-paper-0413/ijsrp-p16135.pdf[2] M. Drela, "Dead-Downwind Faster Than The Wind (DFTTW) Analysis", unpublished https://www.blueplanettimes.com/wp-content/uploads/2010/08/Drela-DDWFTTW-Analysis.pdf[3] Presentation by Rick Cavallaro (from 54:47 until 59:00) //www.youtube.com/watch?v=X6oJpnSJyV8These references contain the same errors. Let us discuss them.
The experiment in the Veritasium video is consistent with the car’s behavior expected in variable wind. The experiment does not prove the possibility of a wind-powered sustained (v=const, a=0) straight-downwind land sailing faster than the wind. Incorrect theoretical arguments are found in the literature.The correct description confirms the intuitive result that, in a steady state (v=const), the speed of the car is always smaller than the speed of the wind. If the car moves faster than the wind, the acceleration is always negative (v≠const, a<0), so that the car decelerates until the speed drops below the speed of the wind.
Gaunaa, et al. describe the physics of rotor-powered vehicles. They describe two cases, one from the vantage point of the earth and the other from the vantage point of the air stream and come to the same conclusions from both frames of reference. They conclude that (apart from forces that resist forward motion):[6]There is no theoretical upper limit to how fast a rotor-driven craft can go directly upwind.Likewise, there is no theoretical upper limit to how fast a rotor-driven craft can go directly downwind.These conclusions hold both for land and water craft.Required for wind-powered vehicle (or water craft) motion are:[6]Two masses moving with respect to each other, e.g. the air (as wind) and the earth (land or water).The ability to change the velocity of either mass with a propeller or a wheel.In the case of a rotor-powered vehicle, there is a drive linkage between the rotor and the wheels. Depending on one's frame of reference—the earth's surface or moving with the air mass—the description of how available kinetic energy powers the vehicle differs:[6]As seen from the vantage point of the earth (e.g. by a spectator), the rotor (acting like a wind turbine) decelerates the air and drives the wheels against the earth, which it accelerates imperceptibly.As seen from the vantage point of the air stream (e.g. by a balloonist), the wheels impede the vehicle—decelerating the earth imperceptibly—and drive the rotor (acting like a propeller), which accelerates the air and propels the vehicle.The connection between the wheels and the rotor causes the rotor to rotate faster with increasing vehicle speed, thereby allowing the rotor blades to continue to obtain forward lift from the wind (as seen from the ground) or to propel the vehicle (as seen from the air stream).[6]
On July 2, 2010, Blackbird set the world's first certified record for going directly downwind, faster than the wind, using only power from the available wind during its run on El Mirage Dry Lake. The yacht achieved a dead downwind speed of about 2.8 times the speed of the wind.[1][16]On June 16, 2012, Blackbird set the world's first certified record for going directly upwind, without tacking, using only power from the wind. The yacht achieved a dead upwind speed of about 2.1 times the speed of the wind.[1]
So your speed with respect to the air around you is zero.What is driving the windmill?
Now, what I'm less sure about is whether you can sail into the wind faster than the wind.
For the windmill to turn, there must be a net wind passing through the propellor disc..If the wind vector over the ground is v and the car is moving downwind at v, there is no net wind passing through the disc.
No. The buck converter, electromechanical inverters, etc., generate less power than they consume, but at a different voltage.
think that an electronic device can't produce higher dc voltage than the battery that powers it.
As mentioned in the article I quoted above, it's the earth.
Quote from: hamdani yusuf on 15/06/2021 23:17:55As mentioned in the article I quoted above, it's the earth.The Earth isn't touching the windmill.
As seen from the vantage point of the air stream (e.g. by a balloonist), the wheels impede the vehicle—decelerating the earth imperceptibly—and drive the rotor (acting like a propeller), which accelerates the air and propels the vehicle.The connection between the wheels and the rotor causes the rotor to rotate faster with increasing vehicle speed, thereby allowing the rotor blades to continue to obtain forward lift from the wind (as seen from the ground) or to propel the vehicle (as seen from the air stream).[6]
Is it possible to make a device that produce temperature higher than 100°C?Is it possible to make a device that produce temperature lower than 0°C?
Third thought: In the optimal scenario, there would be no wind at all. In the reference frame of the vehicle, it's the same air movement across the propeller, but maximum forward movement of the road helping the vehicle. That makes it a perpetual motion machine. I vote no again.
Quote from: hamdani yusuf on 16/06/2021 09:21:54Is it possible to make a device that produce temperature higher than 100°C?Is it possible to make a device that produce temperature lower than 0°C?Yes*.So what?* for example, you could run a "steam" engine from the temperature difference using alcohol as the working fluid.That engine could turn a generator and run an electric fridge or furnace.