You may be right, certainly proponents of this explanation use "centrifugal
force."

However, differential gravity can be explained a number of ways. For example,
the Moon's pull causes the Earth to accelerate towards the Moon. That portion
of the Earth closer feels more force, and thus falls faster; that portion on the
far side feels less force, and thus falls slower. These differences cause the
bulges on the near and far sides.

Remember that Centrifugal Force may be a handy explanation, but it is a
"fictional force" that only appears real to an observer in an accelerating frame
of reference. Therefore, whenever it is used to explain something, there must
be another explanation that works in a non-accelerating frame.



"Nav" wrote in message
...
Jeff,

I think the term centrifuigal is appropriate in this context. It is a
term in the system that can be appreciated without needing to consider
Newtonian forces. To understand centripetal forces is a lot harder than
just demonstrating the effect. similarly gravity can be demonstrated
without maths. Thus the explanation becomes really simple e.g.:

The earth-moon body rotates around a common point and water tries to
move away from the center (water in a bucket swung on a rope analogy).
The moon exerts gravity which is stronger on the side of the moon. Thus
water forms two bulges on opposite sides and makes two tides as the
earth rotates...


Cheers


Jeff Morris wrote:

As I said, I was leaving this as an exercise for the reader.

I have heard tides on the far side of the Earth described in terms of the
centrifugal force caused by the Earth's rotation around Earth-Moon system.
Although this is a consistent way of describing it, I've never liked using
"fictional" forces.

Jeff Morris wrote:

You may be right, certainly proponents of this explanation use "centrifugal
force."

However, differential gravity can be explained a number of ways. For example,
the Moon's pull causes the Earth to accelerate towards the Moon. That portion
of the Earth closer feels more force, and thus falls faster; that portion on the
far side feels less force, and thus falls slower. These differences cause the
bulges on the near and far sides.


I like it! That's a way of putting it I've not heard before and it is
quite elegant (provided the listener can accept that the Earth is
falling toward the Moon!)


Remember that Centrifugal Force may be a handy explanation, but it is a
"fictional force" that only appears real to an observer in an accelerating frame
of reference. Therefore, whenever it is used to explain something, there must
be another explanation that works in a non-accelerating frame.


I could be devious and say we are all in an accelerating frame! But you
are quite right about the artifice of a virtual force. Nevertheless,
children want to know about tides and for them centripetal force can be
experienced more easily than the idea they are on an earth that is
falling...

Cheers