"Bill Hobba" wrote in message
news

"Daniel Weston" wrote in message
...

A few days ago I was explaining to my grandson the Newton Bucket Spin
Experiment. I explained the outcome in terms of centrifugal motion.
But the answer cannot be that simple or it would not be referenced so
often. And something about distant stars.

Can anyone explain the complexity of this experiment? What is the big
deal?

There is no big deal. If you consider the bucket rotating in an inertial
frame then you get the standard curved water shape as a result of
centrifugal forces. But the question is how does the water know how to
curve? - the answer is - because it is rotating relative to an inertial
frame. But wait a minute - an inertial frame is simply a conceptual
conventional standard of rest with a conceptual coordinate system - how
can
acceleration wrt to something conceptual cause the water to curve? The
answer of course is that it is no more a problem than the forces that
appear
when you accelerate wrt to an internal frame (it fact it is a result of
those). To get around these 'problems' Mach proposed it was rotation
relative to the distant stars. It has long been known that a frame at
rest
relative to the distant stars was inertial. This provided the 'thing' it
accelerated relative to when an inertial frame was otherwise just
something
conceptual. Me - I think it is a load of codswallop - but each to their
own. The answer is obvious - Newton's first law is in fact saying the
conceptually there always exits a frame where particles move with constant
velocity unless acted on by a force - whenever we see non inertial forces
appear it is obvious you must be accelerating wrt to some frame - even if
it
is just conceptual. The is not to say Mach's principle is wrong - it may
be
correct - I just think it is not required.

Please see Tom Roberts response. My explanation is crap compared to his.

Thanks
Bill