# Conceptual question about the Coriolis force and the weather

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Even without any wind the trajectories are curved in the inertial frame, because the air masses rotate with the Earth.
Yes, I'm being too sloppy here. I understand that these trajectories are curved because they follow Earth's surface. What I meant was curved with respect to Earth's surface, as one views sattelite photo's (to make it even more obvious, approximate the Earth's surface as being flat, i.e. with its tangent space). But I guess that doesn't really make sense, now I think about it.

As I pointed out in post #12, "what stuff looks like to humans" is a different matter from what the trajectories actually are. You have to decide if you want to discuss physics or human perception of relative motions.
Well, the latter one, but I guess the exact distinction between the two in this particular case is one of my misunderstandings.

By the way, I've always had this kind of confusions, also in discussion about the precise relation between passive and active coordinate transformations in General Relativity, the exact meaning of Lie derivatives, etc. It's sort of my running confusion in my life as a physicist. Everytime I think I have it figured out in one case, I can't reconcile it with the other one. It's a kind of mental relativistic ping-pong :P

So whatever my understanding will be in the end, thanks a lot for all the replies, really appreciated. I'm glad there is a PhysicsForums where I can spit out my confusion without people become annoyed (visibly) ;)

...What I meant was curved with respect to Earth's surface...
You were asking about the trajectories in the inertial frame. The Earth's surface is rotating.

, as one views sattelite photo's.
Static images do not show movement.

Let's make a comparison to the Foucault pendulum
Compare it to an invisible pendulum, that leaves visible traces on the rotating ground below it.

In the inertial frame the invisible pendulum is not deflected, but an inertial human observer who sees only the curved traces on the rotating ground will have a hard time identifying the actual motion in the inertial frame. Especially if he just looks at a static picture, as you do with the satellite image of a hurricane.

See this video at the very end, when the pendulum is hidden:

This might be part of you confusion, the other part is that fluid dynamics is more complex than a pendulum and the air masses have more forces acting on them.

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