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On Jun 3, 2021, at 01:30, Bill Norwood via Phys-l <phys-l@mail.phys-l.org> wrote:
I think that these guys felt that it was necessary to demonstrate success, when, actually, they were not well-tooled enough to do so.
Red flag: These guys are much into their emotions, as a significant amount of screen time is about their emotions
Even if their theory is correct, I believe that reality prevented their proving their theory. Five reasons that I believe reality undid them:
1. There was a 4 or 5 second showing of the gears in the gearbox connecting the axle of JUST ONE of the rear wheels to a shaft which drives the propeller. This caused a sideways torque on the vehicle which would create sideways skidding of the rear wheels, which would waste energy.
If this were a differential as used in automobiles, the rear wheels would have had, on average, equal burdens in driving the propeller, and there would have been no sideways torque.
Have you ever rode an adult tricycle and tried to make a sharp turn in the wrong direction, which does not allow the one driving wheel to rotate?
2. The rear wheels are very narrow, so they would tend to sink a little into the sand - again wasting energy. This is especially true for the one rear wheel that is driving the propeller.
3. I think that the scene where the the fan vehicle nearly tips over as the guy in the towing truck takes too sharp a turn too fast, is just showmanship which would tend to take viewers’ attention away from the flaws in the experiment. (They had decided to move the fan vehicle when the wind direction changed.)
4. After observing that the fan was shaking so badly it would have to be taken apart and balanced, because it was dangerous, they went ahead with the experiment without balancing the fan, while emphasizing the high level of risk.
The trouble with this is that there was no shaking of the fan either before or after their demonstration of the fan’s shaking.
5. The person electing to proceed with the experiment (drive the propeller car) despite the hazards is portrayed, as actually contemplating his own death as a possible result.
This does not make sense. The theory that he seeks to prove clearly does not warrant his risking his life. Sure, if it were wartime and the rapid development of a weapon that would enable winning the war...
Bill Norwood
U of MD at College Park
1966-2018
Sent from my iPhone
On Jun 2, 2021, at 5:14 PM, Daniel MacIsaac via Phys-l <phys-l@mail.phys-l.org> wrote:_______________________________________________
In the Veritasium video they claim the vehicle (a sail car / land car with backwards facing propellor) is pushing back against the oncoming air. So if the air is moving, when pushing downwind if they can reverse the direction of the air approaching the sail, then they can extract more than just 1 unit of momentum. This’d be analogous to the old chestnut of bouncing a rubber ball rather than a clay ball off a door to close it, to get more than 1 mv (2mv if both balls have same mass and velocity) transfer to the door. So by BLOWING back the oncoming air at more than 1mv, they get to go downwind faster than the wind (neglecting other losses). I’m thinking the only surprise here (airboats exist and I’ve seen lots of Everglades boating footage; propellor driver aircraft also exist) is that the Veritasium cart uses gearing driven by the wheels to drive the fan blades so no additional external energy source except the wind.
On Jun 2, 2021, at 22:10, Bill Norwood via Phys-l <phys-l@mail.phys-l.org> wrote:
(In the one-dimensional case) the sailboat’s speed is said to max out at wind speed, but actually it must be less than wind speed, due to the water drag on the boat.
Bill Norwood
U of MD at College Park
Sent from my iPhone
On Jun 2, 2021, at 2:31 PM, Brian Whatcott <betwys1@sbcglobal.net> wrote:_______________________________________________
Here's the directly upwind version of a similar vehiclehttps://www.wired.com/2012/07/wind-powered-car-upwind/?redirectURL=https%3A%2F%2Fwww.wired.com%2F2012%2F07%2Fwind-powered-car-upwind%2F
On Wednesday, June 2, 2021, 01:09:42 PM CDT, Brian Whatcott <betwys1@sbcglobal.net> wrote:
I know of two vehicles that give rise to invective from physics professors: The sand-yacht that rolls directly down wind at twice the speed of the wind
https://www.youtube.com/watch?v=jyQwgBAaBag
Couldn't find a video of a toy boat with a big air propeller driving a small water prop directly upwind.But they exist!
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_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
https://www.phys-l.org/mailman/listinfo/phys-l
Forum for Physics Educators
Phys-l@mail.phys-l.org
https://www.phys-l.org/mailman/listinfo/phys-l
_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
https://www.phys-l.org/mailman/listinfo/phys-l
Forum for Physics Educators
Phys-l@mail.phys-l.org
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