Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: waytogo on 21/11/2012 11:01:56
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Hi,
Any scientific explanation about that? I still have not find anything... tnx
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Tidal braking by the moon slows down Earth's rotation about it's axis, (days are slowly getting longer (http://en.wikipedia.org/wiki/Day_length#Historical_variation_of_day_length_because_of_tidal_acceleration)), conservation of angular momentum transfers Earth's lost (rotational) energy to the moon causing it to travel faster in it's orbit around Earth, a faster orbital speed means is a bigger orbit : the moon slowly moves away from the Earth ... http://en.wikipedia.org/wiki/Tidal_acceleration
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Hi RD, tnx for reply but wikipedia has not references at all concerning the 'explanation' about it.
However do you know if is it an accepted theory? if its true, do you know when it was released?
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There is evidence for tidal acceleration throughout the solar system ... http://en.wikipedia.org/wiki/Tidal_locking#List_of_known_tidally_locked_bodies
A historical perspective here ... http://articles.adsabs.harvard.edu/full/2003A%26G....44b..22S
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.... conservation of angular momentum transfers Earth's lost (rotational) energy to the moon causing it to travel faster in it's orbit around Earth, a faster orbital speed means is a bigger orbit : the moon slowly moves away from the Earth ... http://en.wikipedia.org/wiki/Tidal_acceleration
Anyway, even in wikipedia, what you have wrote (purple text), is not reported as an explanation/fact (it's just your own interpretation) and other links you provided, didn't help very much...
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If it aint in Wiki, it aint true!!! :P
RD, I'm trying to get my head round the idea that the tidal effect would cause the moon to speed up. How is the energy transferred from Earth to moon?
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I think I’ve answered the bit about transfer of energy:
http://www.bbc.co.uk/news/science-environment-12311119
The bit that gives me pause for thought is:
“But the energy gained as the Moon is pushed higher is balanced by a reduction in the energy of its motion - so an acceleration provided by the Earth's tides is actually slowing the Moon down.”
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RD, I'm trying to get my head round the idea that the tidal effect would cause the moon to speed up. How is the energy transferred from Earth to moon?
I think it actually slows the moon down.
The further from the central body, the orbital velocity decreases, and the orbital period increases.
However, it still requires an energy transfer to achieve a higher orbit.
The moon is beyond the geostationary/geosynchronous orbit, and thus the moon orbits slower than the earth rotates. It would be different below the geosynchronous orbit.
The earth rotates at 1 rotation a day.
The moon orbits at 1 orbit a month.
I'm not sure about the tidal energy transfer. If the side of the earth facing the moon has a greater mass than other parts of the planet (tides), then the system would tend to be "sticky" in that direction, and thus they would tend to try to synchronize the speed, except that the more energy transfer to the moon, the slower it goes.
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Ocean tides are caused by the gravitational pull of the Moon (and, to a lesser extent, the Sun). The resulting tidal bulge in Earth's oceans is dragged ahead of the Moon in its orbit due to the daily rotation of Earth. As a consequence, the ocean mass offset from the Earth-Moon line exerts a pull on the Moon and accelerates it in its orbit. Conversely, the Moon's gravitational tug on this mass exerts a torque that decelerates the rotation of Earth. The length of the day gradually increases as energy is transferred from Earth to the Moon, causing the lunar orbit and period of revolution about Earth to increase.
http://eclipse.gsfc.nasa.gov/SEcat5/secular.html
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Wow, that one was one of the shortest explanations I've seen, still making sense RD :)
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... still making sense RD :)
Don't be so sure, I think I've got the bit about the orbital velocity increasing wrong.
The total energy (potential + kinetic) of the moon increases, but it's orbital velocity slows when the radius of the orbit increases ...
(https://upload.wikimedia.org/math/5/4/f/54f7c0c46e004968dd496cc4aa2b4f76.png)
https://en.wikipedia.org/wiki/Orbital_speed#Mean_orbital_speed
The closer the orbiting body the faster its orbital speed ...
(https://upload.wikimedia.org/wikipedia/en/6/69/Kepler-second-law.gif)
https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion
[ It's the inverse square law which is complicating matters (https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation) ]
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Hmm "The length of the day gradually increases as energy is transferred from Earth to the Moon, causing the lunar orbit and period of revolution about Earth to increase." I read that as when the earth 'transfer' energy to the moon it accelerates but as its orbit increase you will from earth find it to 'slow down' as it will be further away, in the same manner as you if looking on a high flying aeroplane find it to move slower over the sky as compared to it being at a lower altitude. As it 'speeds up' (gain energy) relative Earth its orbit must increase as I think of it, to assume that it can go to a 'higher orbit' by losing energy doesn't make sense to me?
But I will read up on it :)
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Oh, I forgot this one when I created this thread:
Why that information about the moon leaving the Earth its not in the school books?
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Oh, I forgot this one when I created this thread:
Why that information about the moon leaving the Earth its not in the school books?
Why should it be? You cannot put all knowledge in schoolbooks, or in university text books. Most things have to be left out. Moreover, i wouldn't be surprised if that particular piece of info was in some school text books somewhere.