Crédito APRH
Já publicamos no nosso blog a explicação da existência das marés. Também explicamos que não se trata de um processo divino.
A maré é causada pela atracção gravitacional do Sol e da Lua. A influência da Lua é bastante superior devido a distância à Terra ser menor do que da Terra ao Sol, apesar da massa da Lua ser muito menor que a da nossa estrela. Matematicamente a maré é uma soma de sinusóides (ondas constituintes) cuja periodicidade é conhecida e depende exclusivamente de factores astronómicos.
A onda formada pelas marés é mais alta na posição onde se encontra a Lua, devido à atração gravitacional. Contudo, no lado oposto da Terra, a inércia excede, em módulo, a força devido à Lua, conforme princípio da ação-reação proposto por Newton, causando assim a mesma elevação nas águas nesse lado oposto. Devido à lei de ação e reação da terceira lei de Newton (além da força centrifuga), a maré ira subir do outro lado da terra tanto quando sobe no lado que está próximo a da lua.
Para saber mais: curiofisica, hidrografico.pt e APRH
Deixo-vos este pequno vídeo com a explicação das marés e o que poderia acontecer se a Lua estivesse mais próxima (clicar em cc para ativar as legendas e escolha português):
(obrigado ao Carlos Portela pela partilha do vídeo)
3 comentários
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Aproveito este post para fazer uma pergunta sobre um mito-urbano (?) comum: o de que nós, como seres humanos essencialmente compostos por água, somos influenciados pela Lua (que afecta as marés). Verdade? Mito? Assim-assim?
Obrigado 🙂
Mito.
abraço
Air tides cause landslides
http://www.nature.com/news/2009/091030/full/news.2009.1052.html
Tenho algumas dúvidas sobre as marés de ar, e também sobre os ínfimos movimentos do solo que serão devidos ás mesmas forças que criam as marés nos oceanos.
O que pensam deste texto?
Citação:
New sudies have shown that not only are there tides in the oceans but also in the earth and the air. Only recently, with very highly sensitive instruments, have scientists been able to see a tidal range of about twenty two inches.
Compared to the oceans tides, that number is very small, but still a change is occurring every day. Also, this crustal tide is due to the same factor as the ocean tides, the sun and the moon. WE can niether se, nor feel it, because like on a ship o the sea, we move with the crust’s flood and ebb.
How did scientists then figure out the earth was movieng, when even the instruments on it would be moving as well? As I said, highly sensitive instruments were used, such as the horizontal pendulum, and the gravimeter, they are used to measure the amount of gravitational pull from the moon.
There is a set standard for these measurments, and after every possible precaution was taken to make sure there were no errors, and the tests were done, there showed a smaller gravitational pull from the moon. The only feasable explanation was that the earth itself had moved, and the instruments with it, altreing the gravtiational pull from the moon. Proving that the earth does, infact, have tides!
Like the oceans, the earth has tow high tides, and two low, the average range being between eight and twelve inches. Also, the flooding and ebbing of the sea auses a downward and upward tilt of the land. When the ocean’s tides are rising millions of gallons of water move into coastal reagions, adding pressure and pushing the land down. When the ocean tides ebb, it relases the pressure, and the crust tilts upward. This wave of motion does not only at end coastal regions though, it extends far inland.
A man named Pierre Simon de Laplace, discovered tides in the air.
It took him eight years of reading his barometer every day four times a day to come to the conclusion that the air also flows similarly to the ocean tides.
Puzzlingly, though, these tides did not follow the moon, as did the ocean, and earth tides, no these tides followed the clock.
High tides were at 10:00 am and pm, and low tides were at 4:00 am and pm. Unlike ocean tides, that flow an hour later each day, these times remained constant, disproving the theory that the tides are following the sun and moon.
Scientists now beleive that they followed the heat of the sun, and that was what caused the pressure to rise and fall. There is some tidal movement like that of the oceans, in the air, but to a very small exatent.
Furhter studies are being done in the outer atmosphere, we have yet to know.
Fonte: http://covenk.tripod.com/index-5.html
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