# Coriolis force - Question about sign

1. ### Curious2013

4
Dear all

I have a question concerning the Coriolis acceleration expression. I learnt it as Ac = -2ω x v, where ω is the vector which indicates the rotation axis direction of Earth and v the velocity of a body that I want to check the Coriolis effect on.

My question: where the minus sign comes from? As far as I understand, it depends on what reference frame I use (inertial or non inertial - the minus comes from the latter, like the Earth, in my conception). Am I correct?

2. ### A.T.

6,460
You can swap ω and v, and the minus sign is gone:

-2ω x v = 2v x ω

The Coriolis force exist only in non inertial frames.

3. ### AlephZero

7,248
The minus sign is there because humans made the arbitrary decision to use right-handed coordinate systems rather than left handed ones.

The Coriolis force is just a consequece of Newton's laws of motion. The physics doesn't depend on what frame you use to describe it, or whether the frame is inertial or non-inertial. The details of the math depend on those things, but "the map is not the country", and similarly "the math is not the phyiscs".

4. ### tiny-tim

26,016
no, it would still be there, because you'd still need v = ω x r