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Does Earth have two high-tide bulges on opposite sides? (2014)

physics.stackexchange.com

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Re: Does Earth have two high-tide bulges on opposite sides? (2014)

#41

Post by hinkley »

antognini wrote: post #17

When I was in grad school in astronomy, one of my professors told me "many a promising young researcher has run their career aground on the rocky shores of tides." The mathematics involved in the theory of tides are formidable. Even in homogeneous, tidally locked systems things can get complicated very quickly. But tides are nevertheless very important. One two objects pass very close to each other, tidal effects are…

There’s been some backpedaling lately in the astrophysics community about whether a tidally locked planet could still maintain an atmosphere and potentially support life. More modeling on how such at atmosphere might work has turned from “no” to “maybe”.

Re: Does Earth have two high-tide bulges on opposite sides? (2014)

#42

Post by s1artibartfast »

IAmBroom wrote: post #16
0xbadcafebee wrote: post #10

[flagged]

We ALL mostly make mistakes throughout our lives. Newton just happened to be much more brilliant than most others - and exhaustively documented his scientific thoughts.

Well some people do nothing worthy of note at all.

Re: Does Earth have two high-tide bulges on opposite sides? (2014)

#43

Post by coolcase »

senderista wrote: post #31
coolcase wrote: post #19

Try to get your head around this while simultaneously not thinking of gravity as a force but curvature in spacetime.

No, don't! Use the simplest model that applies in your context!

I agree, I meant to add "as a mind bending exercise to realize how complex nature is!"

Re: Does Earth have two high-tide bulges on opposite sides? (2014)

#44

Post by CommenterPerson »

Six months ago, I spent a week at the shore. It happened to be full moon. We were out walking late at night while the moon was high up, and had to slog through ankle deep water on the way back. It was like clockwork roughly 12 hours apart.

Did read through stackexchange. It is indeed complicated. But the top response feels like paralysis by analysis. If we analyzed turbulent flow too much we would be unable to build rockets. Remember frictionless planes and point masses in high school? Those results are not exact either but a great way to model and understand what is going on.

Soooo .. could we make simplifying assumptions here? What if the earth was a smooth rigid sphere with a layer of water on the surface? The center of mass of Earth-Moon is at ~3/4ths of the earth's radius, from the earth's center. They are rotating about that center. The 12+ hour tides in many parts of the world start to make sense. Is there a mistake in this mental model?

Re: Does Earth have two high-tide bulges on opposite sides? (2014)

#45

Post by red369 »

CommenterPerson wrote: post #44

Six months ago, I spent a week at the shore. It happened to be full moon. We were out walking late at night while the moon was high up, and had to slog through ankle deep water on the way back. It was like clockwork roughly 12 hours apart. Did read through stackexchange. It is indeed complicated. But the top response feels like paralysis by analysis. If we analyzed turbulent flow too much we would be unable to build…

From reading the accepted StackExchange answer, I think the answer to your last questions is that this model might still be too simplified.

In your simplified model of the Earth, you would also need to make the ocean deep enough that the water could travel fast enough to keep up with the Earth's rotation (~22 km).

Re: Does Earth have two high-tide bulges on opposite sides? (2014)

#46

Post by darkerside »

II2II wrote: post #38
tomxor wrote: post #29

Earlier quoted context omitted.

> So it's a bunch of complicated splashy water that is excited by the moon moving past This explanation is so much better. If people want to use big words they can say fluid dynamics, but yeah, it's a complex system with a big orbiting body pulling on it regularly, that gives the complex system rhythm but not order.

That would be akin to describing a computer as a complicated arrangement of switches that control each other through pulses of electricity to do useful stuff. While it may satisfy a bunch of people who aren't really interested in how computers work, and it may even inspire a few people who are intrigued by how such a simple notion could produce incredible results, it doesn't really explain how computers work.

But it is actually a bit more accurate than saying, electricity goes in and information comes out

Re: Does Earth have two high-tide bulges on opposite sides? (2014)

#47

Post by inetknght »

Calwestjobs wrote: post #35
senderista wrote: post #31

Earlier quoted context omitted.

No, don't! Use the simplest model that applies in your context!

exactly, like water is excellent model for electricity, but youtubers want to be edgy, provocative so they intentionally drop something which needs 20+ years of intentional thinking / education on high schoolers.

I like AlphaPhoenix's video on it.

https://www.youtube.com/watch?v=C3gnNpYK3lo

Re: Does Earth have two high-tide bulges on opposite sides? (2014)

#48

Post by dghlsakjg »

CommenterPerson wrote: post #44

Six months ago, I spent a week at the shore. It happened to be full moon. We were out walking late at night while the moon was high up, and had to slog through ankle deep water on the way back. It was like clockwork roughly 12 hours apart. Did read through stackexchange. It is indeed complicated. But the top response feels like paralysis by analysis. If we analyzed turbulent flow too much we would be unable to build…

Your clock was off. Tides advance ~30 minutes per day. But not exactly 30 minutes. Sometimes more. Sometimes less. Sometimes it doesn’t follow a semi diurnal pattern.

Water can’t pass through landmasses, and that is a huge factor. If the earth had no landmasses, the tides would be entirely as you expect. However, if you look at a global visualization of tidal heights, you will see that a small landmass, NZ is a great example, can have highs and lows just miles apart. Same in Panama, what happens on the pacific coast is wildly different to what happens on the Caribbean.

In addition, the gravity of the sun comes to factor as well. Where I am, north of the 50th parallel, we simply don’t get very low tides during the day when we are near the winter solstice. The opposite happens in the summer.

The timing of the tides for any given spot tend to be predictable (where it is semi diurnal anyway, other places are a mess). But heights are extremely variable.

Re: Does Earth have two high-tide bulges on opposite sides? (2014)

#49

Post by jhanschoo »

CommenterPerson wrote: post #44

Six months ago, I spent a week at the shore. It happened to be full moon. We were out walking late at night while the moon was high up, and had to slog through ankle deep water on the way back. It was like clockwork roughly 12 hours apart. Did read through stackexchange. It is indeed complicated. But the top response feels like paralysis by analysis. If we analyzed turbulent flow too much we would be unable to build…

The SE answer gave you a nice map. The points where the white lines coalesce experience no change in height. The blue regions experience low tidal amplitude, whereas the red regions experience high tidal amplitudes. The white lines are the lines of equal phase: if a point on the line is experiencing its high tide, so is every other point on the line, and likewise for low tide.

As is clear from the map, the tidal response is profoundly affected by land mass and ocean depth, which have complex shapes; so too the tidal response is as complex as it is, which is simple in comparison.

Re: Does Earth have two high-tide bulges on opposite sides? (2014)

#50

Post by rhdjsjebshjffn »

srean wrote: post #6

The problem of predicting tides was so important that it attracted many Physics and Maths heavy weights. You can well imagine how important predicting tides would have been for D-day landing. One related fascinating historical artifact is the special purpose analogue computer designed by Lord Kelvin in the 1860s based on Fourier series, harmonic analysis. Think difference engine in it's cogs and cams glory, but speci…

> You can well imagine how important predicting tides would have been for D-day landing.

Is this intended to communicate positivity or negativity?

Predicting tides was known to the ancients; it would be lovely to explore the hubris of the modern narrative.

Edit: fundamentally, if hacker news has taught me anything, it's that "downvote = makes me feel bad and doesn't want to answer questions". The entire concept of democratic news aggregation was a lie.

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