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From: "Jonathan Thornburg [remove -color to reply]" <dr.j.thornburg@gmail-pink.com>
Newsgroups: sci.physics.research
Subject: Re: The Elevator in Free Fall
Date: 29 Dec 2024 07:20:44 GMT
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In article <vk0k8g$2p4uk$1@dont-email.me>, Luigi Fortunati asked
> Are tidal forces real?

In article <lt1tqbFapkrU1@mid.dfncis.de>, I replied
> They can do work, so they must be real.
> 
> [[...]]
> 
> See
>   https://en.wikipedia.org/wiki/Tidal_power
> for some real-world examples of work done by tidal forces, with (in some
> cases) power output measured in the hundreds of megawatts.  These systems
> all ultimately exploit the fact that g_wrt_Earth is NOT constant from one
> edge of the tidal power basin to the other edge, i.e., that the (entire)
> tidal power basin as NOT a local inertial reference frame.

Oops, that last sentence of mine was quite wrong. :(

The variation in g_wrt_Earth over the tidal power basin is generally
negligible for a tidal power system.  I should have written this instead:

  These systems
  all ultimately exploit the fact that g_wrt_Earth varies with time
  AND varies with position on the Earth's surface.  The combination
  of these variations causes ocean tides (which certainly do mechanical
  work).

I should also point out this GREAT animation of worldwide tides at one
particularly-powerful frequency:

  https://en.wikipedia.org/wiki/File:Global_surface_elevation_of_M2_ocean_tide.webm

-- 
-- "Jonathan Thornburg [remove -color to reply]" <dr.j.thornburg@gmail-pink.com>
   currently on the west coast of Canada
   "[I'm] Sick of people calling everything in crypto a Ponzi scheme.
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                                                 -- Pat Dennis, 2022-04-25