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-   -   Coriolis force - Question about sign (http://www.physicsforums.com/showthread.php?t=659385)

Curious2013 Dec17-12 12:35 AM

Coriolis force - Question about sign
 
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?

Thanks in advance!

A.T. Dec17-12 03:48 AM

Re: Coriolis force - Question about sign
 
Quote:

Quote by Curious2013 (Post 4199757)
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?

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

-2ω x v = 2v x ω

Quote:

Quote by Curious2013 (Post 4199757)
As far as I understand, it depends on what reference frame I use (inertial or non inertial

The Coriolis force exist only in non inertial frames.

AlephZero Dec17-12 01:17 PM

Re: Coriolis force - Question about sign
 
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".

tiny-tim Dec17-12 02:32 PM

Quote:

Quote by AlephZero (Post 4200259)
The minus sign is there because humans made the arbitrary decision to use right-handed coordinate systems rather than left handed ones.

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

(btw, this is a duplicate thread to http://www.physicsforums.com/showthread.php?t=659387)

A.T. Dec17-12 05:03 PM

Re: Coriolis force - Question about sign
 
Quote:

Quote by AlephZero (Post 4200259)
The minus sign is there because humans made the arbitrary decision to use right-handed coordinate systems rather than left handed ones.

To me it seems more like it's the arbitrary decision to have ω first in the term.


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