Physics Help Forum Why Coriolis is always to the Right in N. hemisphere?

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Sep 17th 2017, 12:35 PM #1 Junior Member   Join Date: Jun 2016 Posts: 7 Why Coriolis is always to the Right in N. hemisphere? Authoritative teachings state that in the Northern hemisphere the Coriolis force always deflects a free item movement to the right of its initial free direction. This [Coriolis] force causes moving objects on the surface of the Earth to be deflected to the right (with respect to the direction of travel) in the Northern Hemisphere and to the left in the Southern Hemisphere ("Wikipedia"). All free-moving objects are deflected to the right of their path of motion in the northern hemisphere. The deviation is the result of the earth's rotation and has been named the Coriolis effect ("The Atmosphere", by Lutgens and Tarbuck, 6-th edition, Simon&Schuster, 1995). These sources illustrate, impressively, this effect by showing a right deviated pass of an object that moves free on the Earth or a rotating body. But strangely all illustrations show a pass from the North pole or from the center of rotation to the Equator or to a periphery, when the deviation is yes to the right. I could not find any illustration of the Coriolis deviation for an object moving in a strictly opposite direction. And all my attempts to see how a pass in an opposite direction, from the Equator to the North pole or from a periphery to the center of rotation, will deviate to the right on a body that did not change its rotation direction (like Earth) failed (For such cases the deviation, to my eyes, stubbornly presents itself to the left). Please help me understand this my conundrum. Many thanks for attention.
 Sep 18th 2017, 03:10 PM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,321 To be clear, the phenomenon of moving to the right is true only if the underlying rotating disc is rotating in a counter-clockwise direction, such as the Earth when viewed from over the north pole. If the disc is rotating in a clockwise direction then objects will appear to deflect to the left as they move toward (or away) from the center - this is what happens on Earth as viewed from over the south Pole. One can envision it like this: imagine a rotating disc, like an old phonograph record, and image a small ball that is sitting stationary relative to the disc at the outer edge of the disc. This ball is rotating about the center of the phonograph platter, at a speed equal to the speed of the edge of the platter, or $\displaystyle V_i= \omega R$ where $\displaystyle \omega$ is the rotational velocity of the platter in radians/second and R is the initial distance of the ball from the center of rotation. Now give the ball a push toward the center, so that it begins to roll inward. It's momentum causes it to continue to move at speed V_i in the tangential direction, but the velocity of the surface of the platter decreases as the ball rolls toward the center - due to $\displaystyle v(r) = \omega r$. Hence the ball is moving faster than the surface of the platter, and so relative to the platter's surface moves forward in the direction of the platter's rotation. If the platter is rotating counter-clockwise this will cause the ball to deflect to the right relative to the disc. Hope this helps! Pmb likes this. Last edited by ChipB; Sep 19th 2017 at 07:00 AM.
Sep 18th 2017, 05:03 PM   #3
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 Originally Posted by ChipB To be clear, the phenomenon of moving to the right is true only if the underlying rotating disc is rotating in a counter-clockwise direction, such as the Earth when viewed from over the north pole.
I love it when people post such beautiful explanations like this.

Sep 19th 2017, 07:02 AM   #4
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 Originally Posted by Pmb I love it when people post such beautiful explanations like this.
Thank you for the kind words - you're making me blush!

Sep 19th 2017, 09:24 AM   #5
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 Originally Posted by ChipB Thank you for the kind words - you're making me blush!
Compliments always given when due.

 Sep 19th 2017, 12:22 PM #6 Junior Member   Join Date: Jun 2016 Posts: 7 ChipB: Many THANKS for your fast and very informative reply that has fully explained my question!! It would be very useful and helpful to many if this your explanation is added/included into the Wikipedia article on the Coriolis effect. Best Wishes!!

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