Lol, guys it's not acceleration it's just the exact definition of acceleration. Which is definitely not acceleration.

None of those reference frames are accelerating.

The difference is whether there is a changing velocity or not.

I'm going to assume that you're defining acceleration in that second statement, because I'm not sure if you are and "changing velocity" is literally what acceleration means. In any case, both acceleration and velocity are vectors, both have a direction, and so a person's velocity sure as hell can't be constant when they're going in circles. Ergo, acceleration. I mean that's what force is, mass times acceleration, so if you move and you can feel it you're accelerating. Earth has gravity that can more than cancel it out, but we can't say the same for rides.

Somebody smarter and with more energy than me can probably come up with a rough estimate of the g's being pulled in each picture (ignoring gravity).

Edit: looks like someone did!

We do understand the difference between speed and velocity. It's just that acceleration is the change in velocity over time, not speed.

What? No, the radius just makes the speed "faster", but what really matters is the frequency of rotation.

The merry-go-round is what, 20-25 RPM max? The carnival ride is only like 6-8 RPM. Both are a hell of a lot faster than 1RPD.

Rotation is acceleration towards the center with a velocity perpendicular to the centre. Using a frame of reference that rotates along with the object doesn't change what is physically happening to that object, it just affects the way you observe what's happening. A rotating frame of reference is itself accelerating and each of those frames of reference are accelerating.

We don't feel the Earth's rotation because gravity is accelerating our entire body and surroundings at the same rate, plus it's not just the spinning keeping us in equilibrium; the left over force holds us on the ground.

The other two feel different because it's the structures that provide the acceleration towards the centre, which then pushes on our bodies where it makes contact, and then the structure of our bodies pulls the rest and you can feel the forces of things wanting to move in the direction of inertia but being pulled around the circle instead.

If rotating frames of reference weren't accelerating, turning a car would feel no different from going straight.

This is like the lava and red goo thing