Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

physics.stackexchange.com

Post reply on HN
Print view View original

71–80 of 96 posts

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

#71

Post by arghwhat »

rhdjsjebshjffn wrote: post #50
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 de…

> 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.

Guidelines:

> Please don't comment about the voting on comments. It never does any good, and it makes boring reading.

That it feels bad to not win the popular vote does not make democracy a lie, and there's no surprise in not winning favor when blanket discarding the current topic and describing it as "hubris", while not adding any new or constructive information.

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

#73

Post by srean »

tylervigen wrote: post #67

The explanation is phenomenal. I particularly like the elevation heat map, which helps me intuitively grasp what is going on. This raises a question for me though: why do we show the tidal bulge graphic in any educational context? Like OP, the "far bulge" was always the most surprising and difficult-to-grasp part of the image. But this explanation would indicate that the far bulge is almost totally pointless as a con…

It's an idealized model, accurate if Earth had only a single all encompassing deep ocean. Idealized models are good pedagogic tools to build corrections upon.

It's similar to depiction of projectile motions as parabola s. The trajectories of artillery shells ar not like that, but helps get started.

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

#75

Post by Bjartr »

tylervigen wrote: post #67

The explanation is phenomenal. I particularly like the elevation heat map, which helps me intuitively grasp what is going on. This raises a question for me though: why do we show the tidal bulge graphic in any educational context? Like OP, the "far bulge" was always the most surprising and difficult-to-grasp part of the image. But this explanation would indicate that the far bulge is almost totally pointless as a con…

I expect because without the far bulge, 12 hour tides can't be explained. One bulge would mean 24 hour tides. Not that either explanation is actually correct, but the two bulge explanation matches the obseved periodicity, which is all most people would ever need or care to know about tides these days.

I can't for the life of me understand why graduate level oceanography courses would be teaching it though.

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

#76

Post by randallsquared »

srean wrote: post #73
tylervigen wrote: post #67

The explanation is phenomenal. I particularly like the elevation heat map, which helps me intuitively grasp what is going on. This raises a question for me though: why do we show the tidal bulge graphic in any educational context? Like OP, the "far bulge" was always the most surprising and difficult-to-grasp part of the image. But this explanation would indicate that the far bulge is almost totally pointless as a con…

It's an idealized model, accurate if Earth had only a single all encompassing deep ocean. Idealized models are good pedagogic tools to build corrections upon. It's similar to depiction of projectile motions as parabola s. The trajectories of artillery shells ar not like that, but helps get started.

Well, a single all encompassing deep ocean of something in which waves could travel 1600 km/h, since that's one of the major constraints, too.

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

#78

Post by kevindamm »

dexwiz wrote: post #58
darkerside wrote: post #46

Earlier quoted context omitted.

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

Information and electricity go in and information and heat go out, to be pedantic about a simplification.

Electricity and possibly information, unless you're considering the structure itself to be information. Some ASICs only need to be powered on, for example.

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

#79

Post by kgwgk »

krisoft wrote: post #60
rhdjsjebshjffn wrote: post #50

Earlier quoted context omitted.

> 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 de…

> Is this intended to communicate positivity or negativity? It just says it was important to predict the tides. There is no positivity or negativity to it. Your question doesn’t make sense, hence the downvotes. > Predicting tides was known to the ancients Good. To which ancients? With what accuracy and how far into the future? What techniques did they use? Tell us more. > it would be lovely to explore the hubris of t…

>> Predicting tides was known to the ancients

> Good. To which ancients?

To the ancients of 1944 for sure.

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

#80

Post by chermi »

jxjnskkzxxhx wrote: post #74

So it appears that the answer is that the bulges are a forcing function, not a displacement. Am I the only one skeptical that Newton would confuse a force with a displacement? What am I missing?

Good point. I'd be curious if anyone actually has the text showing he said this. It's in principia I guess. My bet was that he never gave a full description, but rather just said that it is moon/sun that *causes* the tides.-- I'd wager he acknowledged the incompleteness of it. Which would still be mostly accurate. It's hard to imagine him knowing about the complicated tides in England and saying definitively he had a full model of the tides.
Post reply on HN