# How can we tell that "fictitious forces" are not real?

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A.T.
Instead of this wording that I used in my original statement in post #6…
“You can change your inertia/motion without proper acceleration.

This terminology nitpicking is discouraging.
Your original statement makes no sense. How is "inertia" changed here?

Your original statement makes no sense.
Hey, easy there. It might be you who makes no sense.

How is "inertia" changed here?
Seriously? Did you even read post #25?
“… you are associating inertia with mass, while I was clearly associating it with momentum.”

“a deviation from inertial motion (as you have so clearly defined it here) can also be made in GR by moving the gravitational source (as per PeterDonis’s and my previous discussion), and outside of GR by using coordinate acceleration of any type.”

Goodbye.

A.T.
Did you even read post #25?
“… you are associating inertia with mass, while I was clearly associating it with momentum.”
Thus avoid ambiguous words like "inertia".

Mister T
stevendaryl
Staff Emeritus
Thank you for your comments. Also a deviation from inertial motion (as you have so clearly defined it here) can also be made in GR by moving the gravitational source (as per PeterDonis’s and my previous discussion)
I think I missed which post you were talking about. Do you mean that if someone connects a rocket to the moon, and moves it somewhere else, then people in freefall near the moon will feel noninertial motion? I'm not 100% sure, but I don't think that's true. As long as the only forces are gravitational, you're not going to feel any proper acceleration.

and outside of GR by using coordinate acceleration of any type.
Coordinate acceleration doesn't imply noninertial motion, except in the special case in which you are using "inertial coordinates". For example, in polar coordinates $r$ and $\theta$, inertial motion doesn't imply that the coordinate acceleration is zero.

PeterDonis
Mentor
2019 Award
you are associating inertia with mass, while I was clearly associating it with momentum.
Which is not correct.

This terminology nitpicking is discouraging.
The problem is not terminology, as I have already pointed out to you. The problem is that you are getting the physics wrong. See below for further examples.

In fact one aught to be given permission to say such things as “In a gravitational field, a body is accelerated in freefall”. I am quoting Einstein here, but the statement should be allowed not because it was Einstein who said it, or that he said it before modern GR. It should be allowed simply because it is true on its own merits.
No, it isn't. "Acceleration" without qualification, in the context of GR, means proper acceleration, and an object in freefall has zero proper acceleration.

a deviation from inertial motion (as you have so clearly defined it here) can also be made in GR by moving the gravitational source (as per PeterDonis’s and my previous discussion)
Wrong. Moving the gravitational source changes the geometry of spacetime. It does not cause any object to deviate from inertial/free-fall motion.

and outside of GR by using coordinate acceleration of any type.
I don't even understand what this means.

I think that, instead of complaining that we are nitpicking your terminology, you ought to take a step back and actually read the points I and others are making about your incorrect statements of the physics.