>As I said, I'm no physicist, but I do DISagree...
>When I am on a train or in a car or a plane that is accelerating, I do feel a force pushing me back even if I am in a seat (i.e. holding on to the accelerating object).

That is called inertia; it is not exactly a force. A force is what is used to overcome inertia.

The relevant formula here is Newton's Second Law: F=ma (net force = mass times acceleration).

Newton's First Law is just a special case: if there is no force, there is no acceleration (change in velocity).

>Maybe it's called "G", not sure, but I am sure it is there.

"G" is short for gravitation; used popularly as so many multiples of the normal earth gravitation. For instance, if a spaceship (or combat plane, etc.) accelerates at 3G, the pilot will feel 3 times as heavy as under normal Earth gravity. In the case of a spaceship, in outer space, this would require an acceleration of about 30 m/sec/sec.

>As regards the effect during circular motion as I described for the amusement ride, I understand that the force is PUSHING ME out from the center and the wall behind me is stopping me and with not much speed at all I can feel 'stuck' in place. That is, I can lift my feet off of the floor and I do not fall to the floor. I attribute this to (what we learned was) the centrifugal force being stronger than gravity at some point.
>
>cheers

The circular case is just a special case of the linear acceleration case; it is for that reason that I wanted to clarify the simpler linear case first.

In the circular case, the acceleration is towards the center of the circle (the magnitude of the velocity doesn't change, but its direction does).