Spiky conker things
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Assorted gorse bushes
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Dry rocks on a beach
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Wet rocks on a beach
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Reminds me of lots of beaches in Nova Scotia where I grew up ♥️
Huge tides so we'd see a lot of wet rocks!
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Replying to @WeftOfSoul
Meanwhile I grew up a literal stone's throw from the bay with the highest tides in the world, so when I go anywhere with ordinary 2-4m tides it basically feels like there's no tides.
Image below is not my hometown but I had to look for a couple seconds to be certain.
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Tides is something I've been meaning to look into
How can the moon be so far away and be pulling such a huge amount of water this way and that?
Something doesn't add up
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here’s another thing that confuses me: in most places the tides are roughly in a 12-hour cycle, meaning 2 high tides and 2 low tides a day (“semi-diurnal”). the naive analysis using the fact that the moon orbits about once a day would suggest that it ought to be about 24 hours
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We've been doing some more digging but it's still not that clear
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That doesn't, intuitively, to me, explain why high tide is twice a day though, moon-side and far-side. Something I've been looking at in this quest today said something about inertia for that though. Hmm…
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i came across a pdf that claims the key is to account for the centrifugal force of the earth’s rotation but i still don’t grok it and now i’m super confused about wtf an inertial reference frame even is
whoi.edu/cms/files/lect
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Incidentally, I watched this video a week ago and now I think I understand inertial reference frames better.
Centrifugal forces appear when you have a rotating frame of reference (around 8mins in the video).
(featuring Terry Tao & MathOverflow)
youtube.com/watch?v=1VPfZ_
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Replying to
but rotating with respect to *what*? the earth is just hanging out in space! what is it rotating with respect to!!!
My toy brain model for thinking about the centrifugal force is imagining I’m a moon sized giant sitting on the North Pole of the earth, and firing a cannon ball down some line of longitude
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Spacetime (whether a la Newton or Einstein) comes equipped with a connection, which distinguishes inertial trajectories (& thus inertial frames). In a spacetime chart "attached to" a rotating body, the matrix-valued connection 1-form is nonzero. No need to appeal to other bodies.
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The differential geometry of how this works in Newtonian physics is spelled out in this lecture: youtube.com/watch?v=IBlCu1. A more conceptual discussion of what this means for the geometry of the world is in chapters 2 & 3 of Tim Maudlin's "Philosophy of Physics: Space and Time".
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