jfm
Well-known member
Thanks Dom, well said <BG> 
Do tides have anything to do with Soltron?
Do tides have anything to do with Soltron?
Why two tides
- Thread starter DPH
- Start date
KevB
Active member
Re: disagree, trev
Because the gravitational pull from the moon on the water on the opposite side of the earth from the moons orbit is less than the pull on the Earth's surface thus the water bulges. (see below)
The tides which we see in the oceans are due to the pull of the Moon and the Sun. The simplest explanation is that the water on the side of the Earth closest to the Moon is pulled, by the Moon's gravitational force, more strongly than is the bulk of the Earth; whereas the water on the side furthest from the Moon is pulled less strongly than the Earth. The effect is to make bulges in the water on opposite sides of the Earth. The effect of the Sun's pull is similar and the tides that we see are the net effect of both pulls.
Because the gravitational pull from the moon on the water on the opposite side of the earth from the moons orbit is less than the pull on the Earth's surface thus the water bulges. (see below)
The tides which we see in the oceans are due to the pull of the Moon and the Sun. The simplest explanation is that the water on the side of the Earth closest to the Moon is pulled, by the Moon's gravitational force, more strongly than is the bulk of the Earth; whereas the water on the side furthest from the Moon is pulled less strongly than the Earth. The effect is to make bulges in the water on opposite sides of the Earth. The effect of the Sun's pull is similar and the tides that we see are the net effect of both pulls.
paulineb
Active member
Queeries ? Who are they then ?
Pxx
Pxx
KevB
Active member
KevB
Active member
I must be bored
We have one tide because the Moon pulls the water and we have the second because the Earth-Moon system doesn't rotate exactly round the centre of the Earth, but around the centre of gravity of the system called the Barycentre. This means that a bulge of the Earth swings around sending water out in the opposite direction to the Moon
We have one tide because the Moon pulls the water and we have the second because the Earth-Moon system doesn't rotate exactly round the centre of the Earth, but around the centre of gravity of the system called the Barycentre. This means that a bulge of the Earth swings around sending water out in the opposite direction to the Moon
tcm
...
Re: elongated fluids?
hmm. if there was some liquid er iron on a table, and a magnet at one side, the iron would move towards to magnet at the magnet side. It wiouldn't move at the other side too to sort of make it flat due to patented jfm elongation pinciple of fluid somehow stretching out with both arms like yawning.
I don't have a problem with the forces right at the middle of the earth being resolved so everything is all nice, not going too far out, and not too far in towards the sun or the moon. For a fluid nearer the moon, then if it can, fluid will tend to move that way a bit with gravity , and at t'other side it'll move out um cos of the centrifugal force....except er if it was centrifugal force then there's be even more loads of water going outwards nearest the moon. Hmm
Soo, at a midpoint..the forces exactly balance. Nearest the moon there's that extra bit of moon gravity pulling it away from the poles etc towards the bulging bit, no problem. At the middle it's all just balanced. And on the other side there's exactly that much less gravity pulling the water towards the middle of the earth, cos the moon is now further away.
Elongation must be cobblers cos would need to sense what is going on at t'other side of the earth and behave differently as a result - it must be a local effect.
Anyway, the problem will be that if anyone is or isn't satisfied with this, ...why then only one tide in NZ? It's no good saying that there are two tides - one for each island.
hmm. if there was some liquid er iron on a table, and a magnet at one side, the iron would move towards to magnet at the magnet side. It wiouldn't move at the other side too to sort of make it flat due to patented jfm elongation pinciple of fluid somehow stretching out with both arms like yawning.
I don't have a problem with the forces right at the middle of the earth being resolved so everything is all nice, not going too far out, and not too far in towards the sun or the moon. For a fluid nearer the moon, then if it can, fluid will tend to move that way a bit with gravity , and at t'other side it'll move out um cos of the centrifugal force....except er if it was centrifugal force then there's be even more loads of water going outwards nearest the moon. Hmm
Soo, at a midpoint..the forces exactly balance. Nearest the moon there's that extra bit of moon gravity pulling it away from the poles etc towards the bulging bit, no problem. At the middle it's all just balanced. And on the other side there's exactly that much less gravity pulling the water towards the middle of the earth, cos the moon is now further away.
Elongation must be cobblers cos would need to sense what is going on at t'other side of the earth and behave differently as a result - it must be a local effect.
Anyway, the problem will be that if anyone is or isn't satisfied with this, ...why then only one tide in NZ? It's no good saying that there are two tides - one for each island.
hlb
RIP
Re: The Easy Answer.
It's a bit like moving in the bath. All the water goes to one end. Then it rushes back again and goes to the other end. If you do it too much it goes over the top. Thats a tidal wave. Or flood. Get in the bath and have a go!!
Have you sent off Your Stamped. SAE and cheque. Yet.
Haydn
It's a bit like moving in the bath. All the water goes to one end. Then it rushes back again and goes to the other end. If you do it too much it goes over the top. Thats a tidal wave. Or flood. Get in the bath and have a go!!
Have you sent off Your Stamped. SAE and cheque. Yet.
Haydn
tcm
...
Re: nah?
if they were for different reasons, then they would be different heights? Er and anyway the barycentre is "because of the moon". You can't have one tide cos of the moon and another cos of the moon's/earth gravity using another word like barycentre?
if they were for different reasons, then they would be different heights? Er and anyway the barycentre is "because of the moon". You can't have one tide cos of the moon and another cos of the moon's/earth gravity using another word like barycentre?
KevB
Active member
Oh Yeah
The strength of gravity depends on the distance from the source. The closer you are, the stronger the "pull" you feel. The Moon's gravity acts on the Earth; but the diameter of the Earth is large enough in relation to the distance of the Moon that the side of the Earth nearer the Moon feels the Moon's gravity significantly more strongly than the side of the Earth away from the Moon. If you could stand at the center of the Earth you would feel the Moon's gravity somewhere between the two.
This part is tricky, and is the hardest part of this explanation to understand. A drawing of these forces looks like this:
-->...............---->..................------->
far................center................near
side..............of Earth...............side
where the arrows represent the force (and direction) of the Moon's gravity on these three points of the Earth. Now, we measure the gravity of the Earth relative to the center of the Earth; everywhere on the Earth, the center is "down". In a sense, we see the center of the Earth as "at rest". It is mathematically correct to then subtract the force of the Moon on the center of the Earth from the force felt on the near and far sides. This is called vector addition. If we do that, our diagram will look like this:
<-..................X...........................->
far...............center......................near
side.............of Earth....................side
(Note that this drawing is not meant to be exact, but just to give a feel for what's happening).
Now we see that in this sense, the Earth is stretched by the difference in the Moon's gravity across the Earth. We call this effect "tides". Tides are a differential force, that is, they result by the difference in the force of gravity between two points.
That is why there are two tidal bulges on the Earth, one on the near side, and one on the far side. Since water is more flexible than rock, we see the tidal effect strongly in the oceans of the Earth, but barely at all in the ground. However, the rock does bend, by as much as 30 centimeters (about a foot) up and down twice a day!
As it it turns out, the tidal bulges do not line up exactly between the center of the Earth and the Moon. Since the Earth rotates, the bulges are swept forward a bit along the Earth. So picture this: the bulge nearest the Moon is actually a bit ahead of the Earth-Moon line. That bulge has mass; not a lot, but some. Since it has mass, it has gravity, and that pulls on the Moon. It pulls the Moon forward in its orbit a bit. This gives the Moon more orbital energy. An orbit with higher energy has a larger radius, and so as the bulge pulls the Moon forward, the Moon gets farther away from the Earth. This has been measured and is something like a few centimeters a year.
Of course, the Moon is pulling on the bulge as well. Since the Moon is "behind" the bulge (relative to the rotation of the Earth), it is pulling the bulge backwards, slowing it down. Because of friction with the rest of the Earth, this slowing of the bulge is actually slowing the rotation of the Earth! This is making the day get longer. The effect is small, but measureable.
This is also why every few years people that measure such things (chronologists?) need to add a leap second to the year. We use atomic clocks to measure time now, and to do this scientists needed to set these clocks to a standard time. The time chosen was 1900. However, the Earth's rotation is decelerating at a rate of about 0.002 seconds per day per century. It's been about a century since the atomic clocks' standard time, so the Earth is slowing relative to an atomic clock by about 0.002 seconds per day, or about 0.7 seconds per year. Note that this does not mean the Earth is actually slowing its rotation by that amount; it means that a clock set by the rotating Earth loses time at that rate relative to an atomic clock. We add leap seconds to our calendar to get the two clocks aligned.
http://www.badastronomy.com/bad/misc/tides.html
The strength of gravity depends on the distance from the source. The closer you are, the stronger the "pull" you feel. The Moon's gravity acts on the Earth; but the diameter of the Earth is large enough in relation to the distance of the Moon that the side of the Earth nearer the Moon feels the Moon's gravity significantly more strongly than the side of the Earth away from the Moon. If you could stand at the center of the Earth you would feel the Moon's gravity somewhere between the two.
This part is tricky, and is the hardest part of this explanation to understand. A drawing of these forces looks like this:
-->...............---->..................------->
far................center................near
side..............of Earth...............side
where the arrows represent the force (and direction) of the Moon's gravity on these three points of the Earth. Now, we measure the gravity of the Earth relative to the center of the Earth; everywhere on the Earth, the center is "down". In a sense, we see the center of the Earth as "at rest". It is mathematically correct to then subtract the force of the Moon on the center of the Earth from the force felt on the near and far sides. This is called vector addition. If we do that, our diagram will look like this:
<-..................X...........................->
far...............center......................near
side.............of Earth....................side
(Note that this drawing is not meant to be exact, but just to give a feel for what's happening).
Now we see that in this sense, the Earth is stretched by the difference in the Moon's gravity across the Earth. We call this effect "tides". Tides are a differential force, that is, they result by the difference in the force of gravity between two points.
That is why there are two tidal bulges on the Earth, one on the near side, and one on the far side. Since water is more flexible than rock, we see the tidal effect strongly in the oceans of the Earth, but barely at all in the ground. However, the rock does bend, by as much as 30 centimeters (about a foot) up and down twice a day!
As it it turns out, the tidal bulges do not line up exactly between the center of the Earth and the Moon. Since the Earth rotates, the bulges are swept forward a bit along the Earth. So picture this: the bulge nearest the Moon is actually a bit ahead of the Earth-Moon line. That bulge has mass; not a lot, but some. Since it has mass, it has gravity, and that pulls on the Moon. It pulls the Moon forward in its orbit a bit. This gives the Moon more orbital energy. An orbit with higher energy has a larger radius, and so as the bulge pulls the Moon forward, the Moon gets farther away from the Earth. This has been measured and is something like a few centimeters a year.
Of course, the Moon is pulling on the bulge as well. Since the Moon is "behind" the bulge (relative to the rotation of the Earth), it is pulling the bulge backwards, slowing it down. Because of friction with the rest of the Earth, this slowing of the bulge is actually slowing the rotation of the Earth! This is making the day get longer. The effect is small, but measureable.
This is also why every few years people that measure such things (chronologists?) need to add a leap second to the year. We use atomic clocks to measure time now, and to do this scientists needed to set these clocks to a standard time. The time chosen was 1900. However, the Earth's rotation is decelerating at a rate of about 0.002 seconds per day per century. It's been about a century since the atomic clocks' standard time, so the Earth is slowing relative to an atomic clock by about 0.002 seconds per day, or about 0.7 seconds per year. Note that this does not mean the Earth is actually slowing its rotation by that amount; it means that a clock set by the rotating Earth loses time at that rate relative to an atomic clock. We add leap seconds to our calendar to get the two clocks aligned.
http://www.badastronomy.com/bad/misc/tides.html
jfm
Well-known member
Re: elongated fluids?
Bolx TCM
You said "Nearest the moon there's that extra bit of moon gravity pulling it away from the poles etc towards the bulging bit, no problem. At the middle it's all just balanced. And on the other side there's exactly that much less gravity pulling the water towards the middle of the earth, cos the moon is now further away. "
Eh, what's all that about? On the other side there is still the gravitational pull of the moon, ok a bit less becos the moon is furhter away, but it's still pulling in same direction, so why does the water bulge move in the opposite direction, away from the gravitational pull?
Still stand by patented elongation theory, just need to think about it some more to explain it proply, praps soltronise it a bit. Iron filings analogy irrelevant, because we are talking about bodies in space that have momentum and are in free fall towards each other' centres of gravity
Bolx TCM
You said "Nearest the moon there's that extra bit of moon gravity pulling it away from the poles etc towards the bulging bit, no problem. At the middle it's all just balanced. And on the other side there's exactly that much less gravity pulling the water towards the middle of the earth, cos the moon is now further away. "
Eh, what's all that about? On the other side there is still the gravitational pull of the moon, ok a bit less becos the moon is furhter away, but it's still pulling in same direction, so why does the water bulge move in the opposite direction, away from the gravitational pull?
Still stand by patented elongation theory, just need to think about it some more to explain it proply, praps soltronise it a bit. Iron filings analogy irrelevant, because we are talking about bodies in space that have momentum and are in free fall towards each other' centres of gravity
KevB
Active member
I\'m getting really good a cut and paste <NM>
.
.
paulineb
Active member
Re: elongated fluids?
So what happens when it's cloudy and you can't see the moon?
Pxx
So what happens when it's cloudy and you can't see the moon?
Pxx
jfm
Well-known member
QED nah nah TCM!
Thanks KevB. Putting this another way, the combined COG of earth and moon is somewhere on a line connecting the two individual COGs. Fluid round the outside (sea) is further from this combined COG at the far side of the earth from the moon, so less gravitational pull (for that distant bit of sea) towards this combined COG. In other words, elongation
Thanks KevB. Putting this another way, the combined COG of earth and moon is somewhere on a line connecting the two individual COGs. Fluid round the outside (sea) is further from this combined COG at the far side of the earth from the moon, so less gravitational pull (for that distant bit of sea) towards this combined COG. In other words, elongation
duncan
Active member
er if this was the case we would all be going round the moon each day rather than going round the sun each year wouldn't we?
tcm
...
Re: elongated fluids?
hmm. it sound much better if the crucial bit is argued down one side of a page and then turn the page with "therefore". KevB above has found something possibly along the same lines.
elongation monster fluid body wd need to feel in solent what is going on in NZ eg quick you molecules, we're all going sort of flattish now. And anyway it would be a comet-ish with not exactly the same second tide.
hmm. it sound much better if the crucial bit is argued down one side of a page and then turn the page with "therefore". KevB above has found something possibly along the same lines.
elongation monster fluid body wd need to feel in solent what is going on in NZ eg quick you molecules, we're all going sort of flattish now. And anyway it would be a comet-ish with not exactly the same second tide.
jfm
Well-known member
We do. All motion is relative. The sun is 83m miles away, but the moon is right next door. Gravitational force is inversely related to square of the distance. You work it out
davel
Active member
And another thing...
If all the water molecules rush towards the moon to give us a high tide, why do high tide times vary so much within a relatively short distance? For Example Potsmouth and St Mary's (Scilly Isles) are pretty well antiphase at 6 hours difference?
Dave L.
Location: 50 51.0 N 1 18.6 W
If all the water molecules rush towards the moon to give us a high tide, why do high tide times vary so much within a relatively short distance? For Example Potsmouth and St Mary's (Scilly Isles) are pretty well antiphase at 6 hours difference?
Dave L.
Location: 50 51.0 N 1 18.6 W
tcm
...
Re: that\'s what i said!
badly, though. I still think I got the "less gravity" thing at the far side, so the water can sneak off away from the gravity. The fluid elongation theory is just another word for "bulge" which just describes the effect not the cause. And also you didn't do a "method" so B minus for you and KevB gets a C for Copying.
badly, though. I still think I got the "less gravity" thing at the far side, so the water can sneak off away from the gravity. The fluid elongation theory is just another word for "bulge" which just describes the effect not the cause. And also you didn't do a "method" so B minus for you and KevB gets a C for Copying.
jfm
Well-known member
yer right
Dang. Punishment accepted, will do 100 lines. But your iron filings stuff was bolx too. Point is, why then cant anyone explain the double bulge? I've looked at loads of websites a while ago, and they all describe the effect not the cause. No one seems able to explain the cause. Where's Dana Scully when needed
Dang. Punishment accepted, will do 100 lines. But your iron filings stuff was bolx too. Point is, why then cant anyone explain the double bulge? I've looked at loads of websites a while ago, and they all describe the effect not the cause. No one seems able to explain the cause. Where's Dana Scully when needed
milltech
Active member
Re: I\'m sure this was really instructive
but I got halfway down and realised i was losing the will to live. It's been a long day!
John
but I got halfway down and realised i was losing the will to live. It's been a long day!
John
