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closed as not a real question by ja72, Waffle's Crazy Peanut, Chris White, Brandon Enright, Michael Brown May 31 '13 at 9:05

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

Wikipedia is your friend: – Hydro Guy May 29 '13 at 21:10
In what situation or context are you asking? Question needs more information. – ja72 May 29 '13 at 21:13
Well in anything moving on the earth, such as ocean currents. – Ovi May 29 '13 at 21:14
The whole point is that you are on a non-inertial system of coordinates, in the case, one that rotates with earth. If you write down the equations of it, you will perceive that there is a dependence with the angular velocity vector and with the position, in such way that you will probably get a minus sign when you pass through the equator, and so, you get things moving in opposite ways. – Hydro Guy May 29 '13 at 21:21
Use Google to find a classic film, "Frames of Reference" with Hume and Ivey... (Had both of them as profs, a loooong time ago) – DJohnM May 30 '13 at 0:12

The rotation of your coordinate system causes the Coriolis effect. Things move in straight lines, but if your coordinate system is rotating, then the straight lines look curved from the perspective of your coordinate system.

If you want to insist that objects move in straight lines in your coordinate system, then you must invent a fictitious reason why objects are skewing off every which-way. Such a force is called a "Coriolis force". There is no actual force acting upon the objects, they just appear to be curving away due to your rotating coordinate system.

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I understand that but that doesn't explain why objects rotate clockwise in the northern and counterclockwise in the southern hemisphere. – Ovi May 30 '13 at 3:57
Think of rotating a globe and trying to draw a straight line towards the north pole. If the globe is spinning clockwise, the arrow will turn clockwise, no matter what hemisphere you're in. So the rotation alone cannot explain the coriolis effect. – Ovi May 30 '13 at 3:59
@Ovi Your analogy implicitly assumes the Earth is a cylinder. As you have just shown, there is no Coriolis effect when your velocity is parallel to the rotation axis. This agrees with the formula for the Coriolis force, which is proportional to $\vec{\Omega}\times\vec{v}$. Instead think of the other extreme - moving across one of the poles. Your non-inertial, Earthbound coordinates are rotating out from underneath your feet. – Chris White May 30 '13 at 4:15
Ok let's say the globe turns clockwise and we start the line at the south pole. If I move at $any$ angle (except 0 or 180) then the line will curve to the surface. However, the coriolis effect requires that objects turn clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. However, in our situation the line would always turn clockwise since the globe is rotating clockwise. – Ovi May 30 '13 at 4:28

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