Re: The Elevator in Free Fall

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.
    Some crypto projects are pump and dump schemes, while others are pyramid
    schemes.  Others are just standard issue fraud.  Others are just middlemen
    skimming off the top.  Stop glossing over the diversity in the industry."
                                                 -- Pat Dennis, 2022-04-25