Talk:Coriolis force

The direction of the ball from the point of view of an observer as moving from the thrower is described here as going in the opposite sense of motion to that of the turntable (or carroussel). But when altitude winds move northwards from the equator they go eastwards, pushed by coriolis force (and would tend to go round in a clockwise manner if not diverted and reversed by presure gradients that exist on the borders of depressions when moving north). Wouldn't it then go further than the thrower (like the texan boy tossing a paperplane northwards to Nebraska but which lands in Delaware*) instead of apparently marking a delay relative to the motion of the carroussel like is showed here ? To me the curves represented on this page would only be right if the paperplane of the boy landed in california*.. ??? I might be completely mistaken, thanks in advance for your help.

• =https://education.nationalgeographic.org/resource/coriolis-effect/

Samoth Yallavec'h (talk) 14:31, 21 June 2023 (UTC)

I understand what you’re getting at but, I believe your assumption changes completely when mass is taken into account. The paper airplane could also be affected by the famous butterfly in Brazil flapping its wings. A missile? Not so much. Also, bringing winds at altitude into it, don’t apply to the paper airplane. I mean no disrespect, just discussing. SmokeyShyla (talk) 16:48, 13 July 2023 (UTC)

The ball is a free body, moving under inertia. The wind gets dragged along with the Earth by friction with the ground and fluid friction within itself. They are not equivalent situations. A hurricane is more like a spinning ice skater. She pulls her arms inward, and she spins faster in the direction that she is already going. The atmosphere is spinning with the Earth. Low pressure pulls it inward so that it spins faster in the direction that it was already going. It may not be accurate to call it an example of Coriolus force. Constant314 (talk) 23:03, 13 July 2023 (UTC)

@Samoth Yallavec'h: Which image from the simple cases section do you think is contradictory with altitude winds? In the first image (person throwing ball to the center of the carousel, carousel rotating counter-clockwise as seen from above) is akin to the altitude winds you describe - sort of. The caveat here is that the person actually is throwing the ball "north" and "west"-ward in order to hit the pole. In the rightside image, which shows the path in the rotating frame, the ball is being pushed into a clockwise-like curve ("eastward") but again the person has thrown the ball with a bit of "westward" motion in the rotating frame. Essentially, the texan boy threw the paper airplane at california and it ended up in nebraska. --FyzixFighter (talk) 01:32, 14 July 2023 (UTC)

Hello and thank you all for your answers. @FyzixFighter what I can't buy is the idea that the leftside image is representative of the coriolis force acting on both altitude winds moving northwards and the paperplane tossed by the boy. Indeed : in both of these latter situations, a greater amount of rotating speed is accumulated by the objects than by the reference points on earth surface at higher latitudes, inertia causing then both air and paperplanes to go eastward while moving north. But if inertia worked the same way on the ball tossed aboard the carroussel, shouldn't it be charged with cinetic energy and hence, while moving in a centripetal way, go in the same direction as this of the carroussel but even further, therefore counter-clockwise ? Just to make it clear : I am not saying the figure is wrong or doesn't represent what would happen in reality, but just questioning its representativeness of the coriolis effect, which, to me, doesn't appear to depend on any point of view but just on different distances from a rotation axis. Again thank you in advance ! 90.42.24.253 (talk) 12:47, 15 July 2023 (UTC)

@Samoth Yallavec'h: Again I want to confirm that we are talking about the image with the carousel rotating in the counter-clockwise direction. If that is the case, the left figure represents what a stationary observes and therefore there is no Coriolis force/effect present in that image. In the stationary frame the ball travels in a straight line from the thrower to the pole because there are no forces in that plane acting on the ball once it leaves the thrower's hand. One thing that I think is absent from the description of the image is that the thrower, from their perspective, has to aim to the left of the pole in order for the ball to hit the pole. The initial velocity in the rotating frame is not pointed at the pole, but has a clockwise (eastward) component. This is evident in the right figure in that image. The thrower is not throwing the ball strictly centripetally from their perspective. In the thrower's frame, the ball curves and attributes the change in direction to the Coriolis force. But in the left figure, there is no need to invoke a phantom force as the motion of the ball can be attributed to the initial velocity and other real forces.

If the thrower did launch the ball strictly centripetal from their perspective, the stationary observer would not see the initial velocity as pointing at the pole and would not say it was strictly centripetal. The stationary observer would see the ball still move in a straight line, but would not need to invoke a phantom force to explain why it did not hit the pole - it missed because the initial velocity of the ball had both radially inward and tangential components. --FyzixFighter (talk) 15:11, 15 July 2023 (UTC)

To say it differently.

• The ball-thrower is aware that he is on a rotating carousel and makes the appropriate adjustments when he throws the ball.
• If he were unaware that he was on a rotating platform, and threw the ball directly at the target, he might infer that there was an unknown force acting to deflect the ball.
• If he were aware that he was on a rotating platform, and the rotation speed was low enough, like when standing on the Earth, he might ordinarily ignore the fact that the ground beneath him was rotating and then invoke a fictitious Coriolis force to account for the deviation of long trajectories.

Constant314 (talk) 17:52, 15 July 2023 (UTC)

I think this example only adds confusion, because of that appropriate adjustments the thrower apparently makes. At first sight one might think that the ball is deflected to the left, contrary to the actual deflection to the right. It also says "ball tossed ... toward the center" which is incorrect, it is tossed to the left of the center. Lastant rus (talk) 18:47, 29 January 2025 (UTC)

Excuse my elusiveness, yes I was talking about the counter-clockwise rotating carroussel. Ok then if I'm getting it right, the person represented by the blue dot is, in both figures and the matter of view point set aside, not facing the pole but rather looking slightly on its left, even though we see him from above as a stationary observer and though the tossed ball follows a straight line that cuts the center of the carroussel ? And the coriolis effect can still be invoked in the right picture... The boy aiming at California to reach Nebraska helped me out a lot ^^ but just a last question : how is it that we still see the deviated trajectory of depressions and hurricanes from space, where we stand as stationary observers disconnected from earth rotation ? To me it sounds like the left figure here should also represent a deviated trajectory now ^^ I must be taken aback by the effect of the point of view and its importance in the definition of the force... Thank you again ! 90.42.24.253 (talk) 20:04, 15 July 2023 (UTC)

I updated that section with another illustration, I think it should make more sense now. Lastant rus (talk) 00:37, 30 January 2025 (UTC)

(Context: I am a non-mathematician, non-physics major that nonetheless uses Wikipedia to gain better understanding of a wide variety of topics.)

The Intuitive Explanation section should be written such that the explanation is accessible to anyone with a basic knowledge of science, but, to be honest, most people do not have the math to understand the preceding sections and so may get discouraged before they even get this far. The graphic at the beginning of the article is wonderful to show the inertial force. A second animation depicting the effects of the inertial force on a long-range object traveling from the equator towards a pole (or from a middle latitude towards the nearer pole would be great in the introduction. I don’t believe that graphic and the brief explanation would interrupt the introduction too much. That way, the Intuitive Section could be deleted. Comments appreciated. SmokeyShyla (talk) 16:41, 13 July 2023 (UTC)

The article contains the sentence: "The horizontal deflection effect is greater near the poles, since the effective rotation rate about a local vertical axis is largest there, and decreases to zero at the equator." What does that mean?? What is the "effective" rotation rate? I thought on earth the rate at the pole is once a day and the rate at the equator is once a day. Or is this a question of speed? Clearly the speed at the equator (1000 mph) is quite a bit greater than at the pole (0?).

So, this seems like nonsense. I learned in physics class that coriolis is the difference between centripetal and gravitational force (as vectors). So except on the equator, the centripetal force is toward the axis, which is not the same as gravity, which is toward the center of the earth. Thus, coriolis is 0 at the equator and increases to middle latitudes, and imparts a spin. Why isn't this simple explanation included in the article? Roricka (talk) 16:09, 4 June 2025 (UTC)

Literally, the ground turns underneath you. If you were on a frictionless surface, at the pole, the ground would turn 360 degrees per day. At the equator it is zero. At other latitudes, it is in between. You don't notice it because friction keeps you oriented relative to the compass.

• I learned in physics class that coriolis is the difference between centripetal and gravitational force

That is incorrect.

Constant314 (talk) 17:10, 4 June 2025 (UTC)

“That is incorrect”. I was speaking a little loosely, I admit. It’s the difference in DIRECTION of the two vectors that create the spinning motion. If the earth were such that gravity always pointed toward the axis instead of toward the center there would be no coriolis force. Roricka (talk) 21:57, 8 June 2025 (UTC)

There would still be a Coriolis force. This force is caused by the fact that the ground is moving under the projectile. There are Coriolis forces even when there is no gravity.

Note that Coriolis force has two common meanings. The first meaning is a specific effect. The second meaning is all the effects due to a rotating frame of reference, including the first effect. Constant314 (talk) 05:09, 9 June 2025 (UTC)

The formula you gave, the difference between gravity and the rotational acceleration, gives a vector with no east-west component. —Tamfang (talk) 22:50, 10 June 2025 (UTC)

The section quoted here is also unclear to me as it uses too many technical terms. For example, what is horizontal deflection? Next, what is effective rotation rate? The note above indicating that the latter is a reference to the ground turning beneath you, assuming you stayed still (frictionless surface) helps, but needs some improvement and an illustration. Even the phrase, "about a vertical axis" is, in context, confusing. Thus, in that one sentence, which attempts to lend some clarity to the daunting initial paragraphs heavily laden with terminology, little clarity is achieved. The entire article suffers from a lack of approachability. Indeed, there should be a short, detailed, scientific explanation at the start, followed by a laymen's explanation, each of which could be explained in more detail, still keeping the target audience in mind, in labeled sections later in the article. That would allow those looking for the technical description to find it immediately, those looking for a layman's understanding to find it soon after, and for both to get more details after reading further. 141.162.102.54 (talk) 12:12, 1 October 2025 (UTC)

The text in the "Visualization" part is relevant for the geophysical Coriolis force (and the geophysical only) but the title should not be "Visualization". The text relates in fact the deepest understanding of the geophysical Coriolis force. It should be named "Fundamental theory" or similar. This might seem surprising to many but the fundamental theory in the geophysical context and the reason why the Coriolis formula arises for the Earth are complicated, which explains why it deserves a dedicated title. 2A01:E0A:D6:B1B0:D874:45D3:C633:EF67 (talk) 20:56, 27 July 2025 (UTC)

In the Intuitive Explanation section, it says that we should "consider an object, constrained to follow the Earth's surface and moving northward in the Northern Hemisphere". It then proceeds to explain that "As the object moves north it has a tendency to maintain the eastward speed it started with (rather than slowing down to match the reduced eastward speed of local objects on the Earth's surface)..." Wasn't the premise that the object is constrained to follow the surface? To me, this seems like a contradiction. ~2025-35064-82 (talk) 10:11, 20 November 2025 (UTC)

I understood that as the object is forced to stay on Earth's surface (i.e. it cannot be displaced vertically) as it moves, rather than being stuck to a single point. ~ KN2731 {talk · contribs} 17:34, 20 November 2025 (UTC)

Better wording, perhaps: constrained to a constant altitude relative to the surface. —Tamfang (talk) 19:40, 24 November 2025 (UTC)

sounds good. Constant314 (talk) 22:19, 24 November 2025 (UTC)