The Coriolis Effect and how it Affects Objects

Ever looked at the weather news and wondered:

Humm, why do those hurricanes and winds appear to be moving in a spinning direction?
why some appear to be moving clockwise? others counterclockwise?
or even those ocean currents, why do they appear to spiral?

Well, I called upon our dearest google, and landed on something called The Coriolis Effect, or The Coriolis Force, and so began our trip...

A spinning low pressure system over Iceland in a counterclockwise direction

So what is the deal with that Coriolis Force?

Essentially the Coriolis Force is what is identified as an inertial force, or fictitious force that occurs due to the rotating nature of Earth (or for that matter, any other rotating frame reference), and that actually causes the deflection of objects from the perspective of the observer.
It is fictitious, meaning it is an apparent force, since it does not really result from physical interaction between the objects, yet is due to acceleration occurring on a particular object (mass) in reference to the rotating frame (Earth)
Huh, come again ?

Well, let's describe it using in a small illustration:
Take a look at the picture below.

The circle represents the rotating frame (kinda like our Earth), the red dot being the observer (me, or you reading this now :) ), and that black ball would be the object perceived on which we are studying the Coriolis Effect.
So, in the top portion of the image, you can see that the ball actually moves in a straight line while the frame spins and the observer spins along with it.
Meanwhile, looking at it from the observer's perspective, you can clearly see that what he sees is a completely different motion, that of which the black ball took a curve !

So why would things move clockwise or counterclockwise?

This basically relates to where you are on Earth. If you are on the Northern hemisphere, the effect would cause things to deflect to the right, and hence the apparent movement of counter-clockwise. If on the southern hemisphere, then the deflection is left bound, and movement would be clockwise.
Keep in mind, that as you move closer to the poles, the deflection gets larger, and on the equator, it is decreases to zero. And it is this deflection that is characterized as the Coriolis Effect.

Again, let's consider why this happens. If you look at the image below, consider that you (in red) and your friend (in green) are standing across each other, with you being closer to the equator, and your friend much above.
If you were to throw an object, a paper plane towards your friend, while you might think it would get to him in a straight line, again this is where the Coriolis effect deflects it, and to the right. This is basically due to you moving faster than your friend along with Earth rotation, because you are closer to the equator.
In fact, any point on the equator would move faster than any other point on Earth, as Earth is widest at the equator

To explain this further, looking below at the speed and distance traveled along with the rotation of Earth, you can clearly notice your distance - the red distance, is bigger and farther, and hence the speed of movement is higher to cross such distance in the same amount of time, making the plane's speed higher as well. Therefore the paper plane moves towards its destination with a higher velocity and would land ahead of your friend. See both images below:

Similarly, if it was your friend the one throwing the plane towards you, it would deflect to the left because again you are moving faster than he is.

And then his plane would land to your left due to his speed being slower

How noticeable is this effect ?

Well, due to the speed of rotation of Earth, completing a single rotation in approx. 24 hours, the Coriolis effect is rather small on every day objects, and often negligible compared to other forces. Which is why we mostly notice it on large-scale object movements, such as hurricanes, winds, and ocean currents.
It also affects airplanes, rockets, missiles... So airplanes simply don't fly in straight lines, they need to take into consideration Coriolis Effect into their path.

History: Got to give credit

Initially, this effect was first described by Italian scientist Giovanni Battista Riccioli in 1651, whereby he noted that a cannon ball fired to the North actually deflects to the left. Later on in 1749, Euler came up with the relevant equation to calculate the magnitude and direction of the effect, which basically translates as follows :

with a_C being the acceleration of the particle in rotating system, v the velocity of the particle with respect to the system, and Ω the angular velocity
And eventually, it was Gaspard-Gustave Coriolis to whom the effect was officially attributed, due to publishing a paper in 1835 describing all the forces relevant to the Coriolis effect, and effectively characterizing the Coriolis effect as acting in a perpendicular direction to the axis of the object.

Trivia: Does it really affect how flushed toilet water spins?

Not really! At least not to any distinguishable perception. And this is a well known misconception - I probably should have written about that misconception long ago with my misconceptions posts, but hey you can check them out on my blog if you haven't.
And that is actually due again to the slow spinning speed of our planet as explained above. On Jupiter, that might have been the case :)

Hope that as fun and educational to you as it was to me !

@mcfarhat

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