The Coriolis Effect

The Coriolis effect says that anytime you're rotating—whether it's on a playground toy or your home planet—objects moving in straight lines will appear to curve. This bizarre phenomenon affects many things, from the paths of missiles to the formation of hurricanes.

You may have heard that the Coriolis effect makes water in the bathtub spiral down the drain in a certain way, or that it determines the way that a toilet flushes. That’s actually wrong.

Although, as you may have noticed while tracking a hurricane on the news, storms in the Northern Hemisphere spin counterclockwise, while those in the Southern Hemisphere spin clockwise. Why do storms spin in different directions depending on their location? And why do they spin in the first place? The answer is the Coriolis effect.

** PRODUCTION CREDITS
------------------------------------------------------------

- Host, Producer: Greg Kestin
- Filming: Greg Kestin
- Research, Writing: Greg Kestin
Samia Bouzid

- Editing, Animating: Samia Bouzid
Greg Kestin

- Editorial Input: Julia Cort, Ari Daniel
- Science consultants: David Holland, Louis Deslauriers, Kerry Emanuel, Daniel Jacob
- Media: Shutterstock, NASA, ESA
- Special thanks: Harvard Lecture Demonstration Group (Daniel Davis, Allen Crockett, Daniel Rosenberg)
- Special thanks: Entire NOVA team
- From the producers of PBS NOVA © WGBH Educational Foundation - Funding provided by FQXi
- Music provided by APM

[SnoopyDoofie]

This is the best demonstration of the Coriolis effect I've seen yet. But even when you slow it down, it is still hard to grasp.

[thetreatment]

You started off by describing Coriolis and its constituent parts beautifully. But where you referenced it to the Earth is where it all fell to pieces.

You gave a great example of the APPARENT deflection that you see while attached to the spinning reference frame. You showed the ACTUAL path the ball took (straight line) with a view from within the still reference frame.

Then you proceeded to explain the ACTUAL rotation of storms. NOT APPARENT. We don’t see storms APPARENTLY deviate because we spin underneath... They ACTUALLY rotate.

A question: You explained that when you are spinning with a reference frame, and watch a ball travel into the non-spinning reference frame, taking a straight path, is when you witness the APPARENT deviation of the ball.
If i’m not spinning with Jupiter on it’s reference frame, how can i see an apparent deviation?

[LaughingInfidel]

It should be pointed out that the Coriolis force is not a separate force of nature; it's entirely the result of inertia.

The analogy of a rotating platform is confusing because it requires a translation from a sphere to a disk. This step isn't necessary. It's much less confusing and more accurate to say simply that the circle the surface of the earth is following as it rotates is smaller as you move north from the equator, therefore the surface is moving slower than it is to the south. An object thrown north still has that faster speed toward the east, so it curves to the east, or to the right from the thrower's perspective. And when thrown south, it curves west because it isn't going fast enough to the east. All the directions are reversed in the southern hemisphere because going north in the southern hemisphere moves you further from the axis of rotation so the surface is moving faster. While moving north in the northern hemisphere moves you closer to the axis so the surface is going slower.

This is why there's no Coriolis effect on objects moving west or east, as is incorrectly shown in the hurricane animation.

The Coriolis effect is similar to an ice skater spinning faster when she pulls her arms in toward her body.

Also, there's a difference between the earth and the rotating platform. On the rotating platform, the path of the ball is a combination of the tangential momentum and the momentum imparted by the throw. This isn't quite what's happening on the Earth's surface. On the platform, the ball travels in a circle because it's being held. This force disappears when the ball is thrown. On earth it's gravity that keeps objects on the surface moving in a circle. Gravity doesn't disappear when an object is thrown.

It may be helpful to isolate two of the movements. Because the object thrown north is going too fast for the surface there, it takes a straight, diagonal path to the northeast seen from a stationary observer. But to an observer on the surface rotating with the earth, the path appears curved to the east. In other words, the path over the ground is curved because of the rotation of the earth under it. (There's also a curve in a different direction due to the curvature of the earth, but we can ignore that.) The path going to the east is caused by the Coriolis effect; the curvature of that path as seen from a rotating observer is caused by the rotation.

Explaining things well is a skill; understanding something yourself doesn't give you that skill. Understanding the subject is necessary but not sufficient to explain it well.

[fusionx]

By far one of the best explanations of the Coriolis effect on video, great work!

[novapbs]

Thank you so much for making this video, Greg! It's super informative.

[peachtheteach]

How did you build your spinning see saw? I would love to make one for my students!

[moeysonful]

I'm confused. Does that mean the hurricanes aren't actually spinning like that, it's only because the satellite that took the picture is spinning with earth to make it look like they're spinning like that? If it's only due to our frame of reference, how does the coriolis effect cause the trade winds and westerlies?

[moviestogether]

seriosly the best explanation...but I have a question...about the hurricans, when we observe it on earth it is roatating because of where we are standing due to the effect but as an observer in space why do we see the wind bending? shouldn't we see it going in a straight line like the demonstration with the ball?

[AdonisBob]

I think this happens because you continue to move towards the ball after you throw it, which causes you to close some distance between the ball and yourself, which causes you to feel like the balls pattern is curving when from a different individual point of perspective, it is not. It is just your perspective.

[drakekay]

3:23 take some time to try to imagine which vector you should toss the ball, if you wanted it to be caught by the other person... :D

[WhatThePhysics]

Here's a little more detail about water swirling in toilets and bathtubs: The Coriolis Effect is larger the longer something is moving, in time. This is because the effect is caused by, for example, the earth rotating, and the more time that passes the more the earth rotates. Since toilets and bathtubs drain so quickly, there isn't much time to see the results of the Coriolis Effect.

Also, the next video is about a contraption that seems to defy gravity!

[sacred_seeker]

If it is just the product of a frame of reference then how is cyclones actually formed without any force?

[SnoopyDoofie]

The video fails to address one of the most profound questions. If the coriolis is nothing more than an optical illusion because we observe it while we are on the planet moving, how come Jupiter's storm rotates in the direction it does? We are not on Jupiter or moving with Jupiter, so how come we see it rotating the way it does?

[frederickschulze]

I've been doing physics problems related to this effect without really having an intuitive understanding of it. This video was great for helping me grasp it. Thank you so much!

[LawatheMEid]

question: the point of start of the ball is:
1- fixed when the camera is fixed, the course is straight. if we attach the start of the ball with the hands we will get curved course>
2- moving with hands when camera rotating, if the point of ball start fixed in place toward the floor will be straight course.

[ShalK]

So in a way the hurricane is moving with out rotation? Meaning does the "effect" actually give it rotation or is it just the frame of reference that we see it rotating?

[ChefSteve-vxsr]

Your misleading people.
NO sniper or weapons expert makes Coriolis
adjustments, simple not true.
They are for wind and elevation X and Y

NO pilot makes adjustments for the so called
Coriolis effect.
I can take off at an airport, Fly due north for 500
miles, turn around 180deg's, fly due south for 500
miles, low and behold, airports right there.

In short if there were a Coriolis effect, it would
be almost impossible to land a fixed wing aircraft.

[jlipdl]

Master in balistic, never use that force like a variable calculation.
All proyectil lounches use another characteristic, from winds, temperture, frictions, etc...

[shaileshrana]

Great video bro. First time I actually got it.

[MrSkyAndrea]

If the Coriolis effect is what determines the rotation of the whirl, then why, in the Northern hemisphere, cyclones rotates counter-clockwise and anti-cyclones rotates clockwise?