"Jeff Morris" wrote in message
...
"Donal" wrote in message
...
"Martin Baxter" wrote in message
Donal wrote:
So why does the moon seem to have a greater impact on the

tides?

Well duh! Remember F=G*(m'*m")/(d^2),


Emmm... Huh?

What the hell does that mean in English?

Did you not take physics in school?

Sadly, I didn't!

With hindsight, I suspect that I had a poor teacher who managed to make
the
subject appear much duller than it really is.

My high school physics teacher was possibly the worst teacher I ever had -
a
true nut case who shouldn't have been left alone with children.
Fortunately I
found much better teachers in college.



I've still got a suspicion that if we expand your equation, we will find
that the sun has a greater gravitational influence on the earth than the
moon does.

Yes, its does. The direct gravitational pull of the Sun is enormous, much
larger than the Moon's. However, the tides are caused by the difference
in pull
between the near side and the far side.

Sorry! This doesn't make any sense at all. How does the water on the far
side(of the earth) know that there is a different pull on the other side?
Even if you were correct, then there would be a high tide facing the moon, a
low tide at right angles to the moon, and a much lower *high* tide opposite
the moon. The reality is that the HW opposite the moon is only fractionally
smaller.

Centrigugal force explains why there is a high tide on the oppisite side of
the Earth from the moon - if you consider that the two bodies are rotating
around a common centre.

Since the Moon is a lot closer, that
difference is more significant. If you remember any calculus, you'd know
that
differentiating a 1/r^2 function yeilds a 1/r^3 function. The inverse
cube of
the Sun's distance becomes a tiny number compared to the Moon's. The net
result is that the Moon's effect on the tides is 2.2 stronger than the
Sun's.

Tsk...tsk.

The moon only has a stronger effect on tides because the Earth and Moon are
an orbiting pair.

Where's Gilligan when you need him?



Regards


Donal
--