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Old 06-23-2021, 03:57 PM   #31 (permalink)
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Would you please define the road, cart, and any topological or environmental considerations?
The road is a level flat surface, the cart is a small rigid body that has it's weight supported by four wheels mounted on two axles. There is small but positive rolling resistance, and small but positive air resistance. There are no magnetic nor electrostatic attractions nor repulsions. There is no magic nor telekinesis going on.

Our inertial frame of reference is the road, and there is no wind.

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Old 06-23-2021, 04:29 PM   #32 (permalink)
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faster than the rope?

Under the conditions stated, I would conclude that the cart velocity cannot exceed the tow-rope velocity.
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Old 06-23-2021, 09:24 PM   #33 (permalink)
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So a water skier never travels faster than the boat that's pulling him?
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Old 06-24-2021, 03:36 AM   #34 (permalink)
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Under the conditions stated, I would conclude that the cart velocity cannot exceed the tow-rope velocity.
FAMOUS LAST WORDS!!

Prepare to have your mind expanded: (or blown if it was inflated to its limits)




The cart moves 93cm when the string moves 43cm, the cart is 2.16 times as fast as the string, exclamation point, QED, more exclamation points.
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Old 06-24-2021, 04:07 AM   #35 (permalink)
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Quote:
Originally Posted by jakobnev View Post
FAMOUS LAST WORDS!!

Prepare to have your mind expanded: (or blown if it was inflated to its limits)




The cart moves 93cm when the string moves 43cm, the cart is 2.16 times as fast as the string, exclamation point, QED, more exclamation points.
I deliberately haven't entered this overall debate because if I don't know nothin', I say nothin', but wouldn't that just be a simple geared-up windless?

Last edited by JulianEdgar; 06-24-2021 at 04:22 AM..
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Old 06-24-2021, 11:53 AM   #36 (permalink)
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Ha, I actually tried that myself.
All you need is two wheels on an axle and a rope wound up on the axle.
Yes, it definitely works; it is not a trick.

On the cart the rope winds itself up on the axle.
It still gets pulled forward because the rope still moves forward (albeit slower than the cart).
The forward pull on the axle is stronger than the resistance it meets from the wheels, as the axle has a smaller diameter than the wheels so it rolls up the rope more slowly than the forward motion.

Likewise, the surface the blades of the propeller provide moves with the wind but more slowly than the car. Hence the wind is still able to blow against it.
And just like the axle winds up the rope slightly, the gears move the propeller against the wind slowly.

I did a step by step explanation in this post.
If you are still convinced this faster than the wind car thing is impossible or if you don't see how it works, please do go through those steps and tell me which of them sounds wrong.
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Old 06-24-2021, 07:20 PM   #37 (permalink)
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Quote:
Originally Posted by aerohead View Post
* the vehicle, with wind from behind, is a crude square-rigger.
No, it is not. You are starting from this assumption, and so you go wrong from the beginning.

It is not a square-rigger, it is much more like a modern sailboat with triangular sails. Which can and do sail faster than the wind speed. And the sails (the propeller blades) meet the wind at an angle.

-soD
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Old 06-25-2021, 10:15 AM   #38 (permalink)
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faster than the boat

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Originally Posted by ennored View Post
So a water skier never travels faster than the boat that's pulling him?
Not if they're just trailing straight behind the tow-boat, which would be the proper context with respect to Blackbird.
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Old 06-25-2021, 10:22 AM   #39 (permalink)
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video

Quote:
Originally Posted by jakobnev View Post
FAMOUS LAST WORDS!!

Prepare to have your mind expanded: (or blown if it was inflated to its limits)




The cart moves 93cm when the string moves 43cm, the cart is 2.16 times as fast as the string, exclamation point, QED, more exclamation points.
Thanks. I could see the video portion, but no audio.
Can you provide a transcript of what the presenter was saying?
------------------------------------------------------------------------------------
1) Did you notice that the pull-string shortens during the presentation.
2) The string is being wound around a spool within the 'cart'.
3) If there is a spring-powered clock-drive, or battery-powered- motor-spool within the 'cart', this power , added to the 'system', is what's responsible for the phenomena you are experiencing, as the string continuously winds itself onto the spool.
4) A parlor trick.
5) A visual distraction from the actual dynamics.
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Last edited by aerohead; 06-25-2021 at 10:30 AM.. Reason: add data
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Old 06-25-2021, 10:32 AM   #40 (permalink)
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It is frustrating to see how you miss it. I really did not expect that.

You're so convinced it cannot work that you can't bring yourself to studying it in detail.

If you set the blades of the propeller flat, so the wheels make it spin but it does not push the air forward or backward compared to the car, do you agree that the wind will push the car forward, albeit not as fast as the wind?

Now if you alter the angle of the blades so that it pushes slightly against the wind, do you agree that would only increase the pressure on the blades leading to an even greater forward force, although a part of that is needed to overcome the resistance of moving the blades against the wind?

A sailboat cannot sail straight against the wind because its mast does not move relative to the boat. But propeller blades do move and that has the same effect as a sail boat tacking back and forth to end up in a position that is straight against the wind from the starting point.

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