Tides

"Pete Melbourne" <psmvsl@yahoo.com> wrote in message
news:laj6a15kbp23332anohgisfbh99r3kdhgu@4ax.com...
> OK, we have not had a decent discussion for ages...
>
> Why do we get two high tides a day? The moon takes about 25 hours to
> return to the same pace relative to the earth so where does the second
> bulge in the sea level come from?

There's a corresponding tide when the moon is furthest away - on the other
side of the earth - to do with balancing of centripetal forces. There being
two bulges is a more stable arrangement for the spin of the earth. These
bulges don't just come and go of course, they spin around the earth
continuously and at any one point on shore they are perceived as a vertical
rise and fall of water level.

Ken

"Pete Melbourne" <psmvsl@yahoo.com> wrote in message
news:laj6a15kbp23332anohgisfbh99r3kdhgu@4ax.com...
> OK, we have not had a decent discussion for ages...
>
> Why do we get two high tides a day? The moon takes about 25 hours to
> return to the same pace relative to the earth so where does the second
> bulge in the sea level come from?

There's a corresponding tide when the moon is furthest away - on the other
side of the earth - to do with balancing of centripetal forces. There being
two bulges is a more stable arrangement for the spin of the earth. These
bulges don't just come and go of course, they spin around the earth
continuously and at any one point on shore they are perceived as a vertical
rise and fall of water level.

Ken

"Pete Melbourne" <psmvsl@yahoo.com> wrote in message
news:laj6a15kbp23332anohgisfbh99r3kdhgu@4ax.com...
> OK, we have not had a decent discussion for ages...
>
> Why do we get two high tides a day? The moon takes about 25 hours to
> return to the same pace relative to the earth so where does the second
> bulge in the sea level come from?

There's a corresponding tide when the moon is furthest away - on the other
side of the earth - to do with balancing of centripetal forces. There being
two bulges is a more stable arrangement for the spin of the earth. These
bulges don't just come and go of course, they spin around the earth
continuously and at any one point on shore they are perceived as a vertical
rise and fall of water level.

Ken

"Pete Melbourne" <psmvsl@yahoo.com> wrote in message
news:laj6a15kbp23332anohgisfbh99r3kdhgu@4ax.com...
> OK, we have not had a decent discussion for ages...
>
> Why do we get two high tides a day? The moon takes about 25 hours to
> return to the same pace relative to the earth so where does the second
> bulge in the sea level come from?

There's a corresponding tide when the moon is furthest away - on the other
side of the earth - to do with balancing of centripetal forces. There being
two bulges is a more stable arrangement for the spin of the earth. These
bulges don't just come and go of course, they spin around the earth
continuously and at any one point on shore they are perceived as a vertical
rise and fall of water level.

Ken

"Pete Melbourne" <psmvsl@yahoo.com> wrote in message
news:laj6a15kbp23332anohgisfbh99r3kdhgu@4ax.com...
> OK, we have not had a decent discussion for ages...
>
> Why do we get two high tides a day? The moon takes about 25 hours to
> return to the same pace relative to the earth so where does the second
> bulge in the sea level come from?

There's a corresponding tide when the moon is furthest away - on the other
side of the earth - to do with balancing of centripetal forces. There being
two bulges is a more stable arrangement for the spin of the earth. These
bulges don't just come and go of course, they spin around the earth
continuously and at any one point on shore they are perceived as a vertical
rise and fall of water level.

Ken

"Pete Melbourne" <psmvsl@yahoo.com> wrote in message
news:laj6a15kbp23332anohgisfbh99r3kdhgu@4ax.com...
> OK, we have not had a decent discussion for ages...
>
> Why do we get two high tides a day? The moon takes about 25 hours to
> return to the same pace relative to the earth so where does the second
> bulge in the sea level come from?

There's a corresponding tide when the moon is furthest away - on the other
side of the earth - to do with balancing of centripetal forces. There being
two bulges is a more stable arrangement for the spin of the earth. These
bulges don't just come and go of course, they spin around the earth
continuously and at any one point on shore they are perceived as a vertical
rise and fall of water level.

Ken

> OK, we have not had a decent discussion for ages...

Would this count as a "discussion" when we could just copy out of an
encyclopedia? However, since I don't have an encyclopedia (and can't be
bothered to dig out my diver training notes)......

> Why do we get two high tides a day? The moon takes about 25 hours to
> return to the same pace relative to the earth so where does the second
> bulge in the sea level come from?

That question can be answered in many levels of detail. There are lots of
things affecting the tides (I think there's 7 different regular factors that
make up the tidal forecasts, excluding weather etc).
From the moon, you get one bulge on the side near the moon caused by the
direct pull of gravity. Thats probably the obvious one. On the opposite
side, furthest from the moon, one way to think about it is that the gravity
is less strong, and so the water isn't pulled as close to the earth's
surface, and so it can spread out away from the Earth, causing the second
high tide. Thats my preferred explanation anyway, a little simplistic but
gets the basic idea across.
You can go into more detail with the affects of the spin of the Earth etc,
but i'll leave you to look that up :O) If you look up the Admiralty (or
anyone who provides tidal predictions) then most will explain the algorithms
behind them, with all the different factors that affect the tides and how
they work.

David

> OK, we have not had a decent discussion for ages...

Would this count as a "discussion" when we could just copy out of an
encyclopedia? However, since I don't have an encyclopedia (and can't be
bothered to dig out my diver training notes)......

> Why do we get two high tides a day? The moon takes about 25 hours to
> return to the same pace relative to the earth so where does the second
> bulge in the sea level come from?

That question can be answered in many levels of detail. There are lots of
things affecting the tides (I think there's 7 different regular factors that
make up the tidal forecasts, excluding weather etc).
From the moon, you get one bulge on the side near the moon caused by the
direct pull of gravity. Thats probably the obvious one. On the opposite
side, furthest from the moon, one way to think about it is that the gravity
is less strong, and so the water isn't pulled as close to the earth's
surface, and so it can spread out away from the Earth, causing the second
high tide. Thats my preferred explanation anyway, a little simplistic but
gets the basic idea across.
You can go into more detail with the affects of the spin of the Earth etc,
but i'll leave you to look that up :O) If you look up the Admiralty (or
anyone who provides tidal predictions) then most will explain the algorithms
behind them, with all the different factors that affect the tides and how
they work.

David

> OK, we have not had a decent discussion for ages...

Would this count as a "discussion" when we could just copy out of an
encyclopedia? However, since I don't have an encyclopedia (and can't be
bothered to dig out my diver training notes)......

> Why do we get two high tides a day? The moon takes about 25 hours to
> return to the same pace relative to the earth so where does the second
> bulge in the sea level come from?

That question can be answered in many levels of detail. There are lots of
things affecting the tides (I think there's 7 different regular factors that
make up the tidal forecasts, excluding weather etc).
From the moon, you get one bulge on the side near the moon caused by the
direct pull of gravity. Thats probably the obvious one. On the opposite
side, furthest from the moon, one way to think about it is that the gravity
is less strong, and so the water isn't pulled as close to the earth's
surface, and so it can spread out away from the Earth, causing the second
high tide. Thats my preferred explanation anyway, a little simplistic but
gets the basic idea across.
You can go into more detail with the affects of the spin of the Earth etc,
but i'll leave you to look that up :O) If you look up the Admiralty (or
anyone who provides tidal predictions) then most will explain the algorithms
behind them, with all the different factors that affect the tides and how
they work.

David

> OK, we have not had a decent discussion for ages...

Would this count as a "discussion" when we could just copy out of an
encyclopedia? However, since I don't have an encyclopedia (and can't be
bothered to dig out my diver training notes)......

> Why do we get two high tides a day? The moon takes about 25 hours to
> return to the same pace relative to the earth so where does the second
> bulge in the sea level come from?

That question can be answered in many levels of detail. There are lots of
things affecting the tides (I think there's 7 different regular factors that
make up the tidal forecasts, excluding weather etc).
From the moon, you get one bulge on the side near the moon caused by the
direct pull of gravity. Thats probably the obvious one. On the opposite
side, furthest from the moon, one way to think about it is that the gravity
is less strong, and so the water isn't pulled as close to the earth's
surface, and so it can spread out away from the Earth, causing the second
high tide. Thats my preferred explanation anyway, a little simplistic but
gets the basic idea across.
You can go into more detail with the affects of the spin of the Earth etc,
but i'll leave you to look that up :O) If you look up the Admiralty (or
anyone who provides tidal predictions) then most will explain the algorithms
behind them, with all the different factors that affect the tides and how
they work.

David