wedrifid comments on The Correct Contrarian Cluster - Less Wrong

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

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Comment author: wedrifid 23 December 2009 07:00:02AM 0 points [-]

I just watched the video. It's a trick, though probably not intentional. The windsock is mounted directly behind the propeller. So when the vehicle moves and the propeller turns, it blows the windsock backwards, and this is the "proof" that the vehicle is travelling faster than the wind.

The sock shows only that at the point where the sock is mounted the air is going backwards relative to the vehicle. What are the implications of that? Where is the energy required to do this coming from? As the vehicle approached the wind speed what would happen to the sock?

Comment author: PhilGoetz 23 December 2009 07:05:22AM 0 points [-]

Where is the energy required to do this coming from?

From the wind. Which is travelling faster than the vehicle. Except in the immediate vicinity of the propeller.

As the vehicle approached the wind speed what would happen to the sock?

If the vehicle moved exactly at the speed of the wind, with the propeller moving, the air would appear dead still before taking into account the movement of the propeller, and so the sock would be blown strongly out behind the vehicle, making it look as if the vehicle were moving much faster than the wind.

Comment author: wedrifid 23 December 2009 07:24:44AM *  0 points [-]

From the wind. Which is travelling faster than the vehicle. Except in the immediate vicinity of the propeller.

So the parts of the vehicle that are travelling slower than the wind receive energy from the wind but not the propeller? If I took off the propeller would the vehicle go faster or slower?

Comment author: PhilGoetz 23 December 2009 03:05:09PM 0 points [-]

The point is that the propeller blows the sock backwards, regardless of whether the vehicle is moving faster than the wind; and this is shown as proof that it's travelling faster than the wind.

Comment author: Vladimir_Nesov 23 December 2009 03:25:20PM 0 points [-]

The point is that the propeller blows the sock backwards, regardless of whether the vehicle is moving faster than the wind; and this is shown as proof that it's travelling faster than the wind.

It is a very good feature of the video (from rationality test standpoint) that this piece of evidence is compromised: you are handed a conspiracy theory right away, and so when rationalization kicks in, you know what to point to.

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