Chronology Current Month Current Thread Current Date [Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

# Re: [Phys-l] definition of gravity

• From: John Denker <jsd@av8n.com>
• Date: Wed, 09 Nov 2011 11:59:42 -0700

On 11/09/2011 11:33 AM, Aburr@aol.com wrote:

I have found this thread to be particularly interesting, challenging , and
useful.

It's always fun when a topic can cover, in a single sentence,
the foundations of physics /and/ practical applications.

This topic is very poorly handled in most introductory texts.

One post mentioned the gravitational field in a rotating frame. I was going
to calculate that when I had a question of "rotating with respect to
what?"

With respect to a gyroscope or some such. Rotation rate is not
relative.

In more detail:

++ The laws of physics are invariant with respect to velocity.
There is no such thing as absolute motion ... provided we are

++ The laws of physics are invariant with respect angular position.
That is, they are invariant with respect to a change in angle, if
the angle is changed beforehand and does not change during the
experiment.

-- The laws of motion are *not* invariant with respect to angular
velocity. There *is* such a thing as absolute rotation rate.
You can detect this with a gyroscope, with a Foucault pendulum,
with anything that is sensitive to Coriolis forces, et cetera.

-- As a tangentially-related point: The laws of motion are not
invariant with respect to acceleration. There is such a thing as
absolute acceleration, even though there is no absolute velocity.