Harry Veeder wrote:
Stephen A. Lawrence wrote:
When you are actually _in_ a rotating frame, such as a car going around
a corner, you naturally "think" about the situation from the POV of that
frame, and in that frame, the centrifugal force -- and the Coriolis
force -- are both quite real, even though they are /called/ "fictitious"
forces.
In orbit about the Earth you don't feel a centrifugal force.
Well, sure, but then it's balanced by gravity. And besides, you never
"feel" a centrifugal force; you just feel the /centripetal/ force, which
is the "real" one.
In GR gravity is also considered to be an "inertial" force (or a
"fictitious" force). It has all the same properties as other
"fictitious" forces, including, most significantly, that it vanishes in
a locally inertial frame. Equally significant -- and necessary, if it
is to vanish in any frame -- is that gravity affects all materials
equally. If any divergence between inertial and gravitational mass is
ever found, however small it may be, it will be a an enormous blow to
the validity of GR, because it will imply that gravity is /not/ a
fictitious force, after all.
Inertia is now the fictitous force.
Say, rather, that forces due entirely to the _inertia_ of an object are
_inertial_ forces. Then we don't have to deal with the question of
whether they're fictitious or not.
I don't care what the textbooks say, inertia is a fiction
except at the moment of contact.
But what is fiction? And, as Pilot said, what is truth?
It came as a great surprise to me when I took my first serious logic
class and found out that the terms "true" and "false" are merely
defined, not "God given", and you get to choose your own definitions...
Harry
