Tyrrell_McAllister comments on The Correct Contrarian Cluster - Less Wrong

38 Post author: Eliezer_Yudkowsky 21 December 2009 10:01PM

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Comment author: Tyrrell_McAllister 23 December 2009 06:35:17AM *  2 points [-]

Did you read the "Solution" post that Vladimir linked to? What about it was unconvincing? (If it's any comfort, that guy ate enough crow for the both of you ;).)

Comment author: PhilGoetz 23 December 2009 07:56:26AM *  0 points [-]

I read the solution. I don't need to think too deeply about his long, complicated explanation that begins with a detailed and erroneous description of the gears, because I have a short, simple explanation of how the illusion is generated in the video, and a short, simple explanation of why such a device would violate conservation laws, which I gave below.

Comment author: Nick_Tarleton 23 December 2009 07:14:38AM 0 points [-]

It wouldn't have convinced me, if I thought the thing didn't work — it never mentions rolling resistance!

Comment author: Tyrrell_McAllister 23 December 2009 07:29:35AM 1 point [-]

it never mentions rolling resistance!

What do you mean by that term? The post does say this:

What this all means is that you've essentially gotten energy from the friction of the wheels against the ground, and turned it into propulsion. The ground friction is providing a way to make the propellor "tack" against the wind. The nature of the mechanism means that the initial acceleration of the cart is slower than a pure sail-driven system, because the way the propeller spins adds resistance to the wheels via the gearing. But ignoring losses to friction, if the wind is constant, it won't stop it from accelerating - it'll just slow the rate of acceleration.

(Emphasis added.)

Comment author: Nick_Tarleton 23 December 2009 07:31:16AM *  0 points [-]

Okay, it does there, but I refer to this part:

At this point, the pure wind force has fallen to 0, because the cart isn't moving relative to the wind. But the propellor is still producing a force dependent on G, A, and r.

So for the right values of G, A, and r, you'll still be accelerating.

This seems to equivocate between wind/propellor force and net force.

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