"Scout" wrote in message
...
Jeff,
Remember that I first posted that very same sentiment, and even provided a
graphic. I still believe that to be true, but have modified my internal
model, giving allowance for the centrifugal force. I'm not a physicist, but
the way I'm seeing it, there is a middle ground in this discussion. I'm
curious to know if you're discounting centrifugal force as a contributor to
the far bulge.
Scout

I've always said that Centrifugal Force can be used as part of the explanation, as
long as you end up with the same answer. There are several different ways of looking
at this, all valid. (I hope I can get through this without mangling the terms too
badly ...)

The problem with Centrifugal Force is that it is a "fictional force." It is only
needed if you work in a non-inertial, or accelerating reference frame. If you are in
a car going around a curve, your reference frame is accelerating towards the center of
the curve, and thus you feel a Centrifugal Force in the opposite direction. To an
outside observer, the CF doesn't exist, the only force is the car pulling the
passenger around the turn. The outside observer can analyze the situation completely
without invoking CF. (The passenger feels CF push him outward, the observer sees the
car pull the passenger inward.)

In the Earth-Moon system there is gravity pulling both the Earth and Moon around
curves. Because the gravity acts on all objects, we don't notice ourselves being
pulled around. The magnitude of the Centrifugal force is to small to notice, but in
that reference frame it exists. To the outside observer, we're just in freefall,
being pulled inward by gravity.

The problem with CF arises when you look carefully at the math. One pitfall Nav fell
into was trying to calculate CF as a function that varies with the distance to the
barycenter. However, all points on the Earth do not rotate around the barycenter,
only the center does. Other points describe the same circle around nearby points, so
that all points on Earth feel the same Centrifugal Force. (This is a tough concept to
explain in words; its easier to do it graphically. Consider a plate wobbling around a
point but with no rotation - each point on the plate describes the same circle.)

BTW, Nav provided two commonly used formulas, one for gravity and the other for CF.
Although they look quite different, you should appreciate that they are the same,
since the angular velocity is determined by the gravitational force. The CF will be
the same (with the opposite sign) as the gravitational pull at the Earth's center.

Since the CF is a constant force, it can't describe the two bulges in opposite
directions. It is gravity itself that varies with distance. The differential force
can be derived either by subtracting the average gravitational force which causes the
freefall at the center of the Earth, or it can be derived by adding the centrifugal
force. Since the two are the same, except for the sign, the math is identical.

So take your pick, either explanation works, and I'm sure there are others. However,
I hope you can appreciate that explanations like "gravity creates the inner bulge,
centrifugal force creates the outer bulge" makes physicists wince!

"Jeff Morris" wrote
[snip]
So take your pick, either explanation works, and I'm sure there are
others. However,
I hope you can appreciate that explanations like "gravity creates the
inner bulge,
centrifugal force creates the outer bulge" makes physicists wince!

Yes, I can, as I've watched my physics teaching partner wince quite a bit
this week as we discussed this thread. He was quick to cover our whiteboard
with formulas and drawings. It's an interesting thread though, and
notwithstanding my oversimplified analogies, I've learned a lot from it. By
the way, I saw that same wince from a black history professor when I
suggested that the Civil War was fought to free the slaves, and then again
when I suggested to an ancient lit professor that The Odyssey has all the
earmarks of an Arnold Schwarzenegger movie. Probably explains why I like a
good fart joke.
Scout

"Scout" wrote in message
...
"Jeff Morris" wrote
[snip]
So take your pick, either explanation works, and I'm sure there are others. However,
I hope you can appreciate that explanations like "gravity creates the inner bulge,
centrifugal force creates the outer bulge" makes physicists wince!

Yes, I can, as I've watched my physics teaching partner wince quite a bit this week as we
discussed this thread. He was quick to cover our whiteboard with formulas and drawings. It's an
interesting thread though, and notwithstanding my oversimplified analogies, I've learned a lot
from it. By the way, I saw that same wince from a black history professor when I suggested that
the Civil War was fought to free the slaves, and then again when I suggested to an ancient lit
professor that The Odyssey has all the earmarks of an Arnold Schwarzenegger movie. Probably
explains why I like a good fart joke.

Sort of like the wince I got from an African-American/Cherokee friend when I asked him how he was
going to celebrate Columbus Day?

jeff

ps So how does your partner rate my explanations?

"Jeff Morris" wrote
[snip] Sort of like the wince I got from an African-American/Cherokee
friend when I asked him how he was going to celebrate Columbus Day?
Ouch!

ps So how does your partner rate my explanations?
The great mediator saw truth in both models. He was a bit more forgiving of
my "impellor in a great centrifugal pump" analogy, but slapped my wrist for
saying this about centrifugal force: if it feels real, mustn't it be real?
By the time he was done, my head was spinning and yet somehow my brain
seemed to be bulging (quite appropriately) out of both sides of my head. In
the end he called me an English teacher, which is his way of slandering me,
and told me my paltry general science achievements were no match for his
superior physics and math skills. I told him he could forget about me taking
him sailing again and he took it all back.
He's never done the newsgroups though, and was quite impressed with the ease
with which like minded folks could debate a worthy topic.
Scout

Scout,

I was determined not to re-enter this discussion, except to needle Donal
about the 1/4 point.

Your post about your physic teacher gave me enough enjoyment to venture
another post.

Your experience brought back memoirs of mine own days in High School
with my own Physic Teacher about Tides and a Commercial Clammer who help
me learn sailing. By the time I got finished, I had more faith in the
Clammer. He lived in a shed on a float in the middle of the harbor. He
was fond of the booze an when he know enough about any subject to
satisfy himself, then he was satisfied.

His explanation of the Tide, given to me willingly. was; and I quote.
The Moon causes the Tides. It cause high tide because of its pull on
earth, which screws up the pull between the earth and the Sun. Since the
Tides are made up of water, the higher water, under the Moon creates
less water on the other side of the Earth or low Tide. Since the Tide
are water and the pull is less the farther away from the Moon they are
not as high on the side of the earth facing the moon but higher than the
water on the side of the Earth facing away away from the Moon. People
call this difference 1/2 tide. The height of High Tide and Low Tide
along with 1/2 Tides are affected by the Phase of the Moon.

The difference of the location and of the time of tides are caused by
the differences of the rotation of the Earth and the time of revolution
and direction of the Moon

This is explanation has served me well for over 60 years.

Ole Thom

Thanks Thom,
thank God for those ol' salty guys ~ they always manage to keep it real!
Scout

"Thom Stewart" wrote
[snip]
Your post about your physic teacher gave me enough enjoyment to venture
another post.

Your experience brought back memoirs of mine own days in High School
with my own Physic Teacher about Tides and a Commercial Clammer who help
me learn sailing. By the time I got finished, I had more faith in the
Clammer. He lived in a shed on a float in the middle of the harbor. He
was fond of the booze an when he know enough about any subject to
satisfy himself, then he was satisfied.

Scout,

I forgot to mention my old friend. Frank, also told me he had Tide
Tables and Almanics for the heigth and times of the tides and the
position on the Moon.

Ole Thom

Well just to confuse things a bit mo
Even if we only focus on the tide generating potential, there is a
cupple of things that we haven't discussed yet, and one of them has to
do with rotation: "The Coriolis freqency". The other thing one could
include is the "parallax".
I mention this just to make clear that the two models discussed above
both are incomplete.

Peter S/Y Anicula

"Jeff Morris" skrev i en meddelelse
...
"Scout" wrote in message
...
Jeff,
Remember that I first posted that very same sentiment, and even
provided a
graphic. I still believe that to be true, but have modified my
internal
model, giving allowance for the centrifugal force. I'm not a
physicist, but
the way I'm seeing it, there is a middle ground in this
discussion. I'm
curious to know if you're discounting centrifugal force as a
contributor to
the far bulge.
Scout

I've always said that Centrifugal Force can be used as part of the
explanation, as
long as you end up with the same answer. There are several
different ways of looking
at this, all valid. (I hope I can get through this without mangling
the terms too
badly ...)

The problem with Centrifugal Force is that it is a "fictional
force." It is only
needed if you work in a non-inertial, or accelerating reference
frame. If you are in
a car going around a curve, your reference frame is accelerating
towards the center of
the curve, and thus you feel a Centrifugal Force in the opposite
direction. To an
outside observer, the CF doesn't exist, the only force is the car
pulling the
passenger around the turn. The outside observer can analyze the
situation completely
without invoking CF. (The passenger feels CF push him outward, the
observer sees the
car pull the passenger inward.)

In the Earth-Moon system there is gravity pulling both the Earth and
Moon around
curves. Because the gravity acts on all objects, we don't notice
ourselves being
pulled around. The magnitude of the Centrifugal force is to small to
notice, but in
that reference frame it exists. To the outside observer, we're
just in freefall,
being pulled inward by gravity.

The problem with CF arises when you look carefully at the math. One
pitfall Nav fell
into was trying to calculate CF as a function that varies with the
distance to the
barycenter. However, all points on the Earth do not rotate around
the barycenter,
only the center does. Other points describe the same circle around
nearby points, so
that all points on Earth feel the same Centrifugal Force. (This is
a tough concept to
explain in words; its easier to do it graphically. Consider a plate
wobbling around a
point but with no rotation - each point on the plate describes the
same circle.)

BTW, Nav provided two commonly used formulas, one for gravity and
the other for CF.
Although they look quite different, you should appreciate that they
are the same,
since the angular velocity is determined by the gravitational force.
The CF will be
the same (with the opposite sign) as the gravitational pull at the
Earth's center.

Since the CF is a constant force, it can't describe the two bulges
in opposite
directions. It is gravity itself that varies with distance. The
differential force
can be derived either by subtracting the average gravitational force
which causes the
freefall at the center of the Earth, or it can be derived by adding
the centrifugal
force. Since the two are the same, except for the sign, the math is
identical.

So take your pick, either explanation works, and I'm sure there are
others. However,
I hope you can appreciate that explanations like "gravity creates
the inner bulge,
centrifugal force creates the outer bulge" makes physicists wince!

mission accomplished! lol
Scout

"Peter S/Y Anicula" wrote
Well just to confuse things a bit mo
Even if we only focus on the tide generating potential, there is a
cupple of things that we haven't discussed yet, and one of them has to
do with rotation: "The Coriolis freqency". The other thing one could
include is the "parallax".
I mention this just to make clear that the two models discussed above
both are incomplete.

You're absolutely correct. There are numerous effects we're not considering. We've
only attempted to understand the primary cause of two tides a day. Even then, the
math is a bit more complex than the simple formulas we've used.

The parallax effects are certainly significant - they are caused non-circular orbits.
And then there's Lunar declination to fold in.

Of course, spring and neap must be considered - does everyone know when Syzygy is?

And these are just the global effect - there's a whole litany of local effects to
consider. Or you can keep a copy of Eldridge or Reed's handy.



"Peter S/Y Anicula" wrote in message
...
Well just to confuse things a bit mo
Even if we only focus on the tide generating potential, there is a
cupple of things that we haven't discussed yet, and one of them has to
do with rotation: "The Coriolis freqency". The other thing one could
include is the "parallax".
I mention this just to make clear that the two models discussed above
both are incomplete.

Peter S/Y Anicula

"Jeff Morris" skrev i en meddelelse
...
"Scout" wrote in message
...
Jeff,
Remember that I first posted that very same sentiment, and even
provided a
graphic. I still believe that to be true, but have modified my
internal
model, giving allowance for the centrifugal force. I'm not a
physicist, but
the way I'm seeing it, there is a middle ground in this
discussion. I'm
curious to know if you're discounting centrifugal force as a
contributor to
the far bulge.
Scout

I've always said that Centrifugal Force can be used as part of the
explanation, as
long as you end up with the same answer. There are several
different ways of looking
at this, all valid. (I hope I can get through this without mangling
the terms too
badly ...)

The problem with Centrifugal Force is that it is a "fictional
force." It is only
needed if you work in a non-inertial, or accelerating reference
frame. If you are in
a car going around a curve, your reference frame is accelerating
towards the center of
the curve, and thus you feel a Centrifugal Force in the opposite
direction. To an
outside observer, the CF doesn't exist, the only force is the car
pulling the
passenger around the turn. The outside observer can analyze the
situation completely
without invoking CF. (The passenger feels CF push him outward, the
observer sees the
car pull the passenger inward.)

In the Earth-Moon system there is gravity pulling both the Earth and
Moon around
curves. Because the gravity acts on all objects, we don't notice
ourselves being
pulled around. The magnitude of the Centrifugal force is to small to
notice, but in
that reference frame it exists. To the outside observer, we're
just in freefall,
being pulled inward by gravity.

The problem with CF arises when you look carefully at the math. One
pitfall Nav fell
into was trying to calculate CF as a function that varies with the
distance to the
barycenter. However, all points on the Earth do not rotate around
the barycenter,
only the center does. Other points describe the same circle around
nearby points, so
that all points on Earth feel the same Centrifugal Force. (This is
a tough concept to
explain in words; its easier to do it graphically. Consider a plate
wobbling around a
point but with no rotation - each point on the plate describes the
same circle.)

BTW, Nav provided two commonly used formulas, one for gravity and
the other for CF.
Although they look quite different, you should appreciate that they
are the same,
since the angular velocity is determined by the gravitational force.
The CF will be
the same (with the opposite sign) as the gravitational pull at the
Earth's center.

Since the CF is a constant force, it can't describe the two bulges
in opposite
directions. It is gravity itself that varies with distance. The
differential force
can be derived either by subtracting the average gravitational force
which causes the
freefall at the center of the Earth, or it can be derived by adding
the centrifugal
force. Since the two are the same, except for the sign, the math is
identical.

So take your pick, either explanation works, and I'm sure there are
others. However,
I hope you can appreciate that explanations like "gravity creates
the inner bulge,
centrifugal force creates the outer bulge" makes physicists wince!